300+ TOP Antennas & Microwave Engineering MCQs and Answers

Antennas & Microwave Engineering Multiple Choice Questions

1. The major drawback of frequency multipliers is that they have:
a. higher attenuation

b. complex construction methods

c. complex design

d. none of the mentioned

Answer:
c. complex design
Clarification: designing a good quality frequency multiplier is more difficult since it non-linear analysis, matching at multiple frequencies, stability analysis and thermal considerations. considering all these issues for designing a multiplier makes it very complex.

2. Oscillators operating at millimeter wavelength are difficult to realize and are also less efficient.
a. true

b. false

Answer:
a. true
Clarification: as frequency increases to the millimeter wave range, it becomes increasingly difficult to build fundamental frequency oscillators with good power, stability and noise characteristics. an alternative approach is to produce a harmonic of a low frequency oscillator through the use of frequency multiplier.

3. A major disadvantage of frequency multipliers is that they multiply the noise factor along with frequency.
a. true

b. false

Answer:
a. true
Clarification: a disadvantage of frequency multipliers is that noise levels are also increased by the multiplication factor.

4. If a frequency multiplier has a multiplication factor of 10, then the increase in noise level due to frequency multiplication is:
a. 10 db

b. 20 db

c. 25 db

d. 15 db

Answer:
b. 20 db
Clarification: for a frequency multiplier, the increase in noise power is given by 20 log n, where n is the multiplication factor of the multiplier. substituting in the below equation, increase in noise level is 20 db.

5. In a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with at all frequencies other than required harmonic.
a. real impedances

b. reactive impedance

c. complex impedance

d. none of the mentioned

Answer:
b. reactive impedance
Clarification: in a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with reactive impedance at all frequencies other than required harmonic nfo. if the diode junction capacitance has a square –law i-v characteristic , it is necessary to terminate unwanted harmonics with short circuit.

6. Resistive multipliers are more efficient as compared to reactive multipliers.
a. true

b. false

Answer:
b. false
Clarification: resistive multipliers generally use forward biased schottky-barrier diodes to provide non linear characteristic. resistive multipliers have low efficiency but have better bandwidth.

7. Reactive multipliers have a disadvantage that they cannot be used at very high frequencies and they become less efficient.
a. true

b. false

Answer:
a. true
Clarification: at millimeter frequencies, varactor diode exhibits resistive property. hence, at high frequency the multiplier becomes lossy and also does not offer high bandwidth, which is a major disadvantage.

8. For a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is:
a. 50 %

b. 25 %

c. 75 %

d. 12.5 %

Answer:
b. 25 %
Clarification: for a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is given by 1/m2 where m is the multiplication factor. for a factor 2 multiplier, maximum theoretical conversion efficiency is 25 %.

9. is a device that converts electrons to photons or vice-versa.
a. antenna

b. electron gun

c. photon amplifier

d. microwave tube

Answer:
a. antenna
Clarification: antenna is a device that converts electrons into photons or vice versa. a transmitting antenna converts electrons into photons while a receiving antenna converts photons into electrons.

10. The basic equation of radiation that is applied to any antenna irrespective of the type of the antenna is:
a. il= qv

b. iq = lv

c. i/l=q/v

d. none of the mentioned

Answer:
a. il= qv
Clarification: basic equation of radiation is given by il=qv. i is the time change in current, l is the length of the current element, q is the charge v is the acceleration of the charge.

11. When the separation between two lines that carry the TEM wave approaches λ the wave tends to be radiated.
a. true

b. false

Answer:
a. true
Clarification: when the separation between

12. The number of patterns radiation pattern required to specify the characteristic are :
a. three

b. four

c. two

d. five

Answer:
a. three
Clarification: the three patterns required are, θ component of the electric field as the function of the angles as θ and φ, the φ component of the electric field as the function of the angles θ and φ, the phase of these fields as a functions of the angle φ and θ .

13. The beam width of the antenna pattern measured at half power points is called:
a. half power beam width

b. full null beam width

c. beam width

d. none of the mentioned

Answer:
a. half power beam width
Clarification: the beam width of an antenna measure at half of the maximum power received by an antenna or the 3 db beam width of the antenna is termed as half null beam width.

14. An antenna has a field pattern of E (θ) = cos2 θ, θ varies between 0 and 900. Half power beam width of the antenna is:
a. 330

b. 660

c. 12000

d. none of the mentioned

Answer:
b. 660
Clarification: half power beam width of the antenna is obtained by equating the field pattern of the antenna to 0.707 (half power point) and finding θ. 2θ gives the value of beam width. solving the given problem in the

15. An antenna has a field pattern E (θ) =cos θ. cos 2θ. The first null beam width of the antenna is:
a. 450

b. 900

c. 1800

d. 1200

Answer:
b. 900
Clarification: half power beam width of the antenna is obtained by equating the field pattern of the antenna to 0.707 (half power point) and finding θ. 2θ gives the value of beam width. twice the half power beam width gives the first null beam width. with the same steps applied, the half power beam width of the antenna is 450. first null beam width is 900.

16. The solid area through which all the power radiated by the antenna is:
a. beam area

b. effective area

c. aperture area

d. beam efficiency

Answer:
a. beam area
Clarification: the beam area is the solid angle through which all of the power radiated by the antenna would stream if p (θ, φ) maintained its maximum value over beam area and zero elsewhere. this value is approximately equal to the angles subtended by the half power points of the main lobe in the two principal planes.

17. Power radiated from an antenna per unit solid angle is called radiation intensity.
a. true

b. false

Answer:
a. true
Clarification: power radiated from an antenna per unit solid angle is called radiation

18. A is a device that converts a guided electromagnetic wave on a transmission line into a plane wave propagating in free space.
a. transmitting antenna

b. receiving antenna

c. radar

d. mixer

Answer:
a. transmitting antenna
Clarification: a transmitting antenna is a device that converts a guided electromagnetic wave on a transmission line into a plane wave propagating in free space. it appears as an electrical circuit on one side, provides an interface with a propagating plane wave.

19. Antennas are bidirectional devices.
a. true

b. false

Answer:
a. true
Clarification: antennas can be used both as

20. Dipole antennas are an example for:
a. wire antennas

b. aperture antennas

c. array antennas

d. none of the mentioned

Answer:
a. wire antennas
Clarification: dipoles, monopoles, oops, yagi-uda arrays are all examples for wire antennas. these antennas have low gains, and are mostly used at lower frequencies.

21. antennas consist of a regular arrangement of antenna elements with a feed network
a. aperture antennas

b. array antennas

c. printed antennas

d. wire antennas

Answer:
b. array antennas
Clarification: array antennas consist of a regular arrangement of antenna elements with a feed network. pattern characteristics such as beam pointing angle and side lobe levels can be controlled by adjusting the amplitude and phase excitation of array elements.

22. A parabolic reflector used for reception with the direct broadcast system is 18 inches in diameter and operates at 12.4 GHz. The far-field distance for this antenna is:
a. 18 m

b. 13 m c) 16.4 m d) 17.3 m

Answer:
d.
Clarification: far field distance for a reflector antenna is given by 2d2/λ. d is the diameter and λ is the operating signal wavelength.

23. of an antenna is a plot of the magnitude of the far field strength versus position around the antenna.
a. radiation pattern

b. directivity

c. beam width

d. none of the mentioned

Answer:
a. radiation pattern
Clarification: radiation pattern of an antenna is a plot of the magnitude of the far field strength versus position around the antenna. this plot gives the detail regarding the region where most of the energy of antenna is radiated, side lobes and beam width of an antenna.

24. Antennas having a constant pattern in the azimuthal plane are called
a. high gain antenna

b. omni directional antenna

c. unidirectional antenna

d. low gain antenna

Answer:
b. omni directional antenna
Clarification: omni directional antennas radiate em waves in all direction. if the radiation pattern for this type of antenna is plotted, the pattern is a constant signifying that the radiated power is constant measured at any point around the antenna.

25. Beam width and directivity are both measures of the focusing ability of an antenna.
a. true

b. false

Answer:
a. true
Clarification: beam width and directivity are both measures of the focusing ability of an antenna. an antenna with a narrow main beam will have high directivity, while a pattern with low beam will have low directivity.

26. If the beam width of an antenna in two orthogonal planes are 300 and 600. Then the directivity of the antenna is:
a. 24

b. 18

c. 36

d. 12

Answer:
b. 18
Clarification: given the beam width of the antenna in 2 planes, the directivity is given by 32400/θ*∅, where θ,∅ are the beam widths in the two orthogonal planes. substituting in the equation, directivity of the antenna is 18.

27. If the power input to an antenna is 100 mW and if the radiated power is measured to be 90 mW, then the efficiency of the antenna is:
a. 75 %

b. 80 %

c. 90 %

d. insufficient data

Answer:
c. 90 %
Clarification: antenna efficiency is defined as the ratio of radiated power to the input power to the antenna. substituting the given data in the efficiency equation, the efficiency of the antenna is 90%.

28. If an antenna has a directivity of 16 and radiation efficiency of 0.9, then the gain of the antenna is:
a. 16.2

b. 14.8

c. 12.5

d. 19.3

Answer:
a. 16.2
Clarification: gain of an antenna is given by the product of radiation efficiency of the antenna and the directivity of the antenna.

29. Gain of an antenna is always greater than the directivity of the antenna.
a. true

b. false

Answer:
b. false
Clarification: gain of an antenna is always smaller than the directivity of an antenna. gain is given by the product of directivity and radiation efficiency. radiation efficiency can never be greater than one. so gain is always less than or equal to directivity.

30. A rectangular horn antenna has an aperture area of 3λ × 2λ. Then the maximum directivity that can be achieved by this rectangular horn antenna is:
a. 24 db

b. 4 db

c. 19 db

d. insufficient data

Answer:
c. 19 db
Clarification: given the aperture dimensions of an antenna, the maximum directivity that can be achieved is 4π a/λ2, where a is the aperture area and λ is the operating wavelength. substituting the given values in the above equation, the maximum directivity achieved is 19 db.

31. A rectangular horn antenna has an aperture area of 3λ × 2λ. If the aperture efficiency of an antenna is 90%, then the directivity of the antenna is:
a. 19 db

b. 17.1 db

c. 13 db

d. 21.1 db

Answer:
b. 17.1 db
Clarification: given the aperture dimensions of an antenna, the directivity that can be achieved is ap4π a/λ2, where a is the aperture area and λ is the operating

32. A resistor is operated at a temperature of 300 K, with a system bandwidth of 1 MHz then the noise power produced by the resistor is:
a. 3.13×10-23 watts

b. 4.14×10-15 watts

c. 6.14×10-15 watts

d. none of the mentioned

Answer:
b. 4.14×10-15 watts
Clarification: for a resistor noise power produced is given by ktb, where t is the system temperature and b is the bandwidth. substituting in the above expression, the noise power produced is 4.14×10-15 watts.

33. With an increase in operating frequency, the background noise temperature:
a. increases

b. decreases

c. remains constant

d. remains unaffected

Answer:
a. increases
Clarification: the plot of frequency v/s background noise temperature shows that with the increase of the signal frequency, the

34. The noise temperature of an antenna is given by the expression:
a. radtb + (1-rad) tp

b. (1-rad) tp

c. radtb

d. none of the mentioned

Answer:
a. radtb + (1-rad) tp
Clarification: the noise temperature of an antenna is given by the expression radtb + (1-rad) tp. here, tb is the brightness temperature and tp is the physical

35. Low is the G/T ratio of an antenna, higher is its efficiency.
a. true

b. false

Answer:
b. false
Clarification: in the g/t ratio of an antenna, g is the gain of an antenna and t is the antenna noise temperature. higher the g/t ratio of an antenna better is the performance of the antenna.

36. has a constant power spectral density.
a. white noise

b. gaussian noise

c. thermal noise

d. shot noise

Answer:
a. white noise
Clarification: thermal noise has a power spectral density for a wide range of frequencies. its plot of frequency v/s noise power is a straight line parallel to y axis.

37. Slotted line is a transmission line configuration that allows the sampling of:
a. electric field amplitude of a standing wave on a terminated line

b. magnetic field amplitude of a standing wave on a terminated line

c. voltage used for excitation

d. current that is generated by the source

Answer:
a. electric field amplitude of a standing wave on a terminated line
Clarification: slotted line allows the sampling of the electric field amplitude of a standing wave on a terminated line. with this device, swr and the distance of the first voltage minimum from the load can be measured, from this data, load impedance can be found.

38. A modern device that replaces a slotted line is:
a. digital cro

b. generators

c. network analyzers

d. computers

Answer:
c. network analyzers
Clarification: although slotted lines used to be the principal way of measuring unknown

39. If the standing wave ratio for a transmission line is 1.4, then the reflection coefficient for the line is:
a. 0.16667

b. 1.6667

c. 0.01667

d. 0.96

Answer:
a. 0.16667
Clarification: ┌= (swr-1)/ (swr+1). substituting for swr in the above equation for reflection co-efficient, given swr is 1.4, reflection co-efficient is 0.16667.

40. If the reflection coefficient of a transmission line is 0.4, then the standing wave ratio is:
a. 1.3333

b. 2.3333

c. 0.4

d. 0.6

Answer:
b. 2.3333
Clarification: swr= (1+┌)/ (1-┌). where ┌ is the reflection co-efficient. substituting for the reflection co-efficient in the equation, swr is 2.3333.

41. In the expression for phase of the reflection coefficient, Lmin stands for :
a. distance between load and first voltage minimum

b. distance between load and first voltage maximum

c. distance between consecutive minimas

d. distance between a minima and immediate maxima

Answer:
a. distance between load and first voltage minimum
Clarification: lmin is defined as the distance between the terminating load of a transmission line and the first voltage minimum that occurs in the transmission line due to reflection of waves from the load end due to mismatched termination.

42. If the normalized load impedance of a transmission line is 2, then the reflection co- efficient is:
a. 0.33334

b. 1.33334

d. 1

Answer:
a. 0.33334
Clarification: zl=z0 (1+┌)/ (1-┌), this is the expression for load impedance. normalized load impedance is the ratio of load impedance to the characteristic impedance, taking zll/z0 as 2, the reflection co-efficient is equal to 0.33334.

43. Link budget consists of calculation of
a. useful signal power

b. interfering noise power

c. useful signal & interfering noise power

d. none of the mentioned

Answer:
c. useful signal & interfering noise power
Clarification: the link analysis and its output, the link budget consists of calculations and tabulations of useful signal power and interfering noise power at the receiver.

44. Which is the primary cost for degradation of error performance?
a. loss in signal to noise ratio

b. signal distortion

c. signal distortion & loss in signal to noise ratio

d. none of the mentioned

Answer:
c. signal distortion & loss in signal to noise ratio
Clarification: there are two primary causes for the degradation of error performance.

45. Which factor adds phase noise to the signal?
a. jitter

b. phase fluctuations

c. jitter & phase fluctuations

d. none of the mentioned

Answer:
c. jitter & phase fluctuations
Clarification: when a local oscillator is used in signal mixing, phase fluctuations and jitter adds phase noise to the signal.

46. Antennas are used
a. as transducer

b. to focus

c. as transducer & to focus

d. none of the mentioned

Answer:
c. as transducer & to focus
Clarification: antennas are used as transducer that converts electronic signals to electromagnetic fields and vice versa. they are also used to focus the electromagnetic energy in the desired direction.

47. Mechanism contributing to a reduction in efficiency is called as
a. amplitude tapering

b. blockage

c. edge diffraction

d. all of the mentioned

Answer:
d. all of the mentioned
Clarification: mechanism contributing to a reduction in efficiency is called as amplitude tapering, spillover, edge diffraction, blockage, scattering, re-radiation and dissipative loss.

48. Space loss occurs due to a decrease in
a. electric field strength

b. efficiency

c. phase

d. signal power

Answer:
a. electric field strength
Clarification: due to the decrease in electric field strength there will be a decrease in signal strength as a function of distance. this is called as space loss.

49. Antenna’s efficiency is given by the ratio of
a. effective aperture to physical aperture

b. physical aperture to effective aperture

c. signal power to noise power

d. losses

Answer:
a. effective aperture to physical aperture
Clarification: the larger the antenna aperture the larger is the resulting signal power density in the desired direction. the ratio of effective aperture to physical aperture is the antenna’s efficiency.

50. Effective radiated power of an isotropic radiator can be given as a product of
a. radiated power and received power

b. effective area and physical area

c. transmitted power and transmitting gain

d. receiving power and receiving gain

Answer:
c. transmitted power and transmitting gain
Clarification: an effective radiated power

51. A dipole antenna is also called as?
a. marconi antenna

b. yagi antenna

c. bidirectional antenna

d. hertz antenna

Answer:
d. hertz antenna
Clarification: one of the most widely used antenna types is the half-wave dipole antenna. this antenna is also formally known as the hertz antenna after heinrich hertz, who first demonstrated the existence of electromagnetic waves.

52. The impedance at the center of the antenna is known as?
a. characteristic impedance

b. radiation resistance

c. transmission impedance

d. recovery resistance

Answer:
b. radiation resistance
Clarification: the transmission line is connected at the center. the dipole has an impedance of 73 v at its center, which is the radiation resistance. at the resonant frequency, the antenna appears to be a pure resistance of 73 v.

53. What happens when the radiation resistance of the antenna matches the characteristic impedance of the transmission line?
a. no transmission occurs

b. no reception occurs

c. swr is maximum

d. swr is minimum

Answer:
d. swr is minimum
Clarification: when the radiation resistance of the antenna matches the characteristic impedance of the transmission line, the swr is minimum and maximum power reaches the antenna. this allows maximum power to be transmitted.

54. The type of dipole antenna that has a higher band width is called as?
a. conical antenna

b. yagi antenna

c. helical antenna

d. marconi antenna

Answer:
a. conical antenna
Clarification: a common way to increase bandwidth in the antenna is to use a version of the dipole antenna known as the conical antenna. the overall length of the antenna is 0.73λ or 0.73(984)/f = 718.32/f. this is longer than the traditional one-half wavelength of a dipole antenna, but the physical shape changes the necessary dimensions for resonance.

55. The radiation pattern of a half-wave dipole has the shape of a
a. doughnut

b. sphere

c. hemisphere

d. circular

Answer:
a. doughnut
Clarification: the radiation pattern of any antenna is the shape of the electromagnetic energy radiated from or received by that antenna. typically that radiation is concentrated in a pattern that has a recognizable geometric shape. the radiation pattern of a half-wave dipole has the shape of a doughnut.

56. What is the beam width for a half wave dipole antenna?
a. 90°

b. 180°

c. 50°

d. 250°

Answer:
a. 90°
Clarification: the beam width is measured between the points on the radiation curve that are 3 db down from the maximum amplitude of the curve. the maximum amplitude of the pattern occurs at 0° and 180°. the 3-db down points are 70.7 percent of the maximum. the angle formed with two lines extending from the center of the curve to these 3-db points is the beam width. the beam width is 90°. the smaller the beam width angle, the more directional the antenna.

57. What does the beam width of an antenna tell us?
a. signal strength

b. signal power

c. directivity

d. degradation

Answer:
c. directivity
Clarification: the measure of an antenna’s directivity is beam width, the angle of the radiation pattern over which a transmitter’s

58. What is the power radiated by the antenna with gain called as?
a. critical power

b. transverse power

c. effective radiated power

d. transmitted power

Answer:
c. effective radiated power
Clarification: the power radiated by an antenna with directivity and therefore gain is called the effective radiated power (erp).

59. What is the radiation pattern of an isotropic radiator?
a. doughnut

b. sphere

c. hemisphere

d. circular

Answer:
b. sphere
Clarification: an isotropic radiator is a theoretical point source of electromagnetic energy. the e and h fields radiate out in all directions from the point source, and at any given distance from the point source, the fields form a sphere.

60. What is the impedance of the folded dipole antenna?
a. 50Ω

b. 100Ω

c. 300Ω

d. 20Ω

Answer:
c. 300Ω
Clarification: a popular variation of the half- wave dipole is the folded dipole. like the standard dipole, it is one-half wavelength long. however, it consists of two parallel conductors connected at the ends with one side open at the center for connection to the transmission line. the impedance of this

61. Which of the following antennas produce a vertical radiation pattern?
a. dipole antenna

b. yagi antenna

c. marconi antenna

d. hertz antenna

Answer:
c. marconi antenna
Clarification: the same effect as dipole antenna can be achieved with a one-quarter wavelength antenna or marconi antenna. a vertical dipole with the doughnut-shaped radiation pattern, in which one-half of the pattern is below the surface of the earth. this is called a vertical radiation pattern.

62. The members of the antenna family which are made of wires of certain value in terms of operating wavelength are called:
a. loop antennas

b. wire antennas

c. dipole antenna

d. slot antennas

Answer:
c. dipole antenna
Clarification: wires of half wavelength are termed as dipoles. their radiation resistance is about 73 Ω. if only half of this length is used, then it is called quarter-wave monopole with a radiation resistance of 36.5 Ω.

63. The antenna in which location of the feed determines the direction of the lobe are:
a. wire antenna

b. loop antenna

c. helical antenna

d. horn antenna

Answer:
a. wire antenna
Clarification: in a wire antenna, the location of the feed determines the direction of the lobe and the orientation of the wire determines the polarization. these wires can be thick or thin. thickness of the wire determines the radiation resistance of the antenna.

64. Based on the size of the loops, loop antennas are classified as small and large loops. This is the only classification of loop antenna.
a. true

b. false

Answer:
b. false
Clarification: loop antennas are classified based on various antenna parameters. to name a few, small and large loops, circular and square loops, loops having single or multi turns, loops with turns wound using a single wire or multiple wires.

65. Antenna that does not belong to the horn antenna family among the following are:
a. pyramidal horn

b. conical horn

c. bi-conical horn

d. none of the mentioned

Answer:
d. none of the mentioned
Clarification: all of the above mentioned antennas belong to the horn antenna family. horn antennas may be made of pointed or rounded waveguides. the waveguides may contain disc at an end or some dielectric.

66. Reflector antennas are widely used to modify radiation patterns of radiating elements.
a. true

b. false

Answer:
a. true
Clarification: reflector antennas are used to modify radiation patterns of radiating elements. reflector antennas are classified into two categories. they are passive reflectors and active reflectors. based on the type of the radiating element and the modification in the radiation pattern required, accordingly either active or passive reflectors are chosen.

67. The pattern of the reflector in a reflector antenna is called:
a. primary pattern

b. secondary pattern

c. reflector pattern

d. none of the mentioned

Answer:
b. secondary pattern
Clarification: in a reflector antenna, the feed pattern is called primary pattern and the pattern of the reflector is called secondary pattern. these antennas are widely employed in radars and other types of point to point communication links.

68. antennas have gain less than reflector antennas but have more lenient tolerance on surfaces.
a. helical antennas

b. lens antennas

c. array antennas

d. slot antennas

Answer:
b. lens antennas
Clarification: lens antennas are complex in nature but are able to scale wider angles. in comparison to reflectors, their gain is 1 or 2 db less, but these have more lenient tolerance on surfaces. these have less rearward reflection, relatively low loss and can be easily shaped to the desired contours.

69. Lens antennas are classified into two types. One being fast antenna, the other one is:
a. slow antenna

b. delay antenna

c. dynamic antenna

d. none of the mentioned

Answer:
b. delay antenna
Clarification: in delay lenses, the electrical path length is increased or the wave is retarded by the lens medium. dielectric lenses and h-plane metal lenses fall in this category.

70. The antennas which offer high operational bandwidth and the antenna parameters are maintained over a wide range of antennas are called:
a. wide band antennas

b. array antennas

c. parabolic antennas

d. none of the mentioned

Answer:
a. wide band antennas
Clarification: in this class of antennas, constancy of impedance and radiation characteristics is maintained over a wide range of frequencies. to be wide band or frequency independent, antennas should expand or contract in proportion to the wavelength.

71. High directivity required in RADAR communication is satisfied using this type of antennas:
a. wide band antennas

b. antenna arrays

c. slot antennas

d. patch antennas

Answer:
b. antenna arrays
Clarification: higher directivity is the requirement in point to point communication. this can be achieved by increasing the size of the antennas in terms of electrical length.

72. The terminal impedance of a dipole antenna is 710 Ω. The terminal impedance of the slot antenna given the intrinsic impedance of air is 377 Ω is:
a. 100 Ω

b. 50 Ω

c. 25 Ω

d. none of the mentioned

Answer:
b. 50 Ω
Clarification: the terminal impedance zs of the slot is given by the relation z 2/ 4z ) zₒ is

73. When the separation between two lines that carry the TEM wave approaches λ the wave tends to be radiated.
a. true

b. false

Answer:
a. true
Clarification: when the separation between two lines that chary the tem wave approaches λ the wave tends to be radiated so that the opened – out line act as an antenna which lunches a free space wave.

74. An antenna has a field pattern of E (θ) = cos2 θ, θ varies between 0 and 900. Half power beam width of the antenna is:
a. 330

b. 660

c. 12000

d. none of the mentioned

Answer:
b. 660
Clarification: half power beam width of the antenna is obtained by equating the field pattern of the antenna to 0.707 (half power point) and finding θ. 2θ gives the value of beam width. solving the given problem in the same flow, half power beam width of the antenna is 660.

75. Power radiated from an antenna per unit solid angle is called radiation intensity.
a. true

b. false

Answer:
a. true
Clarification: power radiated from an antenna per unit solid angle is called radiation intensity. unit of radiation intensity is watts per steridian or per square degree.

76. Antennas are bidirectional devices.
a. true

b. false

Answer:
a. true
Clarification: antennas can be used both as transmitters and receivers. as transmitters they radiate energy to free space and as receivers they receive signal from free space. hence, they are called bidirectional devices as they are used at both transmitting end and receiving end.

77. Dipole antennas are an example for:
a. wire antennas

b. aperture antennas

c. array antennas

d. none of the mentioned

Answer:
a. wire antennas
Clarification: dipoles, monopoles, oops, yagi-uda arrays are all examples for wire

78. antennas consist of a regular arrangement of antenna elements with a feed network
a. aperture antennas

b. array antennas

c. printed antennas

d. wire antennas

Answer:
b. array antennas
Clarification: array antennas consist of a regular arrangement of antenna elements with

79. Antennas having a constant pattern in the azimuthal plane are called
a. high gain antenna

b. omni directional antenna

c. unidirectional antenna

d. low gain antenna

Answer:
b. omni directional antenna
Clarification: omni directional antennas radiate em waves in all direction. if the

80. If the power input to an antenna is 100 mW and if the radiated power is measured to be 90 mW, then the efficiency of the antenna is:
a. 75 %

b. 80 %

c. 90 %

d. insufficient data

Answer:
c. 90 %
Clarification: antenna efficiency is defined as the ratio of radiated power to the input power to the antenna. substituting the given

81. Which of the following is false regarding Antenna array?
a. directivity increases

b. directivity decreases

c. beam width decreases

d. gain increases

Answer:
b. directivity decreases
Clarification: a single antenna provides low gain and less directivity. to increase the directivity antenna arrays are used. with the antenna arrays, directivity and gain increases and beam width decreases.

82. Electrical size of antenna is increased by which of the following?
a. antenna array

b. decreasing the coverage area

c. increasing the coverage area

d. using a single antenna

Answer:
a. antenna array
Clarification: to increase the directivity antenna arrays are used. with the antenna arrays, directivity and gain increases and beam width decreases. the electrical size of the antenna is increased by placing an array antenna together to achieve high directivity.

83. For long distance communication, which of the property is mainly necessary for the antenna?
a. high directivity

b. low directivity

c. low gain

d. broad beam width

Answer:
a. high directivity
Clarification: long distance communication requires antenna with high directivity. to increase the directivity antenna arrays are used. with the antenna arrays, directivity and gain increases and beam width decreases.

84. Which of the following is false about the single antenna for long distance communication?
a. enlarging may create side lobes

b. no side lobes

c. high directivity is required

d. high gain is required

Answer:
b. no side lobes
Clarification: high directive antennas are required for the long distance communications. the array of antennas is used to increase the directivity. the directivity can be increased by increasing the dimensions of antenna but it creates side lobes.

85. The electrical size of antenna is increased by antenna array to avoid size lobes compared to single antenna.
a. true

b. false

Answer:
a. true
Clarification: increasing the dimensions of antennas may lead to the appearance of the side lobes. so by placing a group of antennas together the electrical size of antenna can be increased. with the antenna arrays, directivity and gain increases and beam width decreases.

86. Total resultant field obtained by the antenna array is given by which of following?
a. vector superposition of individual field from the element

b. maximum field from individual sources in the array

c. minimum field from individual sources in the array

d. field from the individual source

Answer:
a. vector superposition of individual field from the element
Clarification: the total resultant field is obtained by adding all the fields obtained by the individual sources in the array. an array containing n elements has the resultant field equal to the vector superposition of individual field from the elements.

87. If the progressive shift in antenna array is equal to zero then it is called
a. broad side

b. end-fire

c. yagi-uda

d. fishbone antenna

Answer:
a. broad side
Clarification: the total phase difference of the fields is given by Ѱ=kdcosθ+β

88. What is the progressive phase shift of the end-fire array?
a. 0

b. 90 c) 180

c. d) 60

Answer:
c. d) 60
Clarification: the progressive phase shift of the end-fire array is 180°. it is a linear array whose direction of radiation is along the axis of the array. for a broadside array it is 0°.

89. Which of the following statement about antenna array is false?
a. field pattern is the product of individual elements in array

b. field pattern is the sum of individual elements in array

c. resultant field is the vector superposition of the fields from individual elements in array

d. high directivity can be achieved for long distance communications

Answer:
b. field pattern is the sum of individual elements in array
Clarification: the total resultant field is obtained by adding all the fields obtained by the individual sources in the array. radiation pattern is obtained by multiplying the individual pattern of the element. field pattern is the product of individual elements in array. antenna arrays are used to get high directivity with less side lobes.

90. are used in the final stages of radar and radio transmitters to increase the radiated power level.
a. power amplifiers

b. oscillators

c. transistors

d. attenuators

Answer:
a. power amplifiers
Clarification: power amplifiers are used in the final stages of radar and radio transmitters to increase the radiated power level. output of power amplifiers are in the range of 100- 500 mw.

91. Important factors to be considered for power amplifier design are:
a. efficiency

b. gain

c. thermal effect

d. all of the mentioned

Answer:
d. all of the mentioned
Clarification: as per the application requirement and considering various aspects of an amplifier like efficiency, gain, thermal efficiency and inter modulation distortion, amplifiers need to be designed.

92. 1 MICROWAVE PASSIVE COMPONENTS: DIRECTIONAL COUPLER, POWER DIVIDER, MAGIC TEE ATTENUATOR, RESONATOR
a. true

b. false

Answer:
a. true
Clarification: power amplifier is the primary consumer of dc power in most hand-held wireless devices, so amplifier efficiency is an important consideration. amplifier efficiency is the ratio of rf output power to dc input power.

93. Gain of power amplifiers with increase in operating frequency.
a. increases

b. decreases

c. increases exponentially

d. decreases exponentially

Answer:
b. decreases
Clarification: silicon bipolar junction transistor amplifiers in the cellular telephone band of 800-900 mhz band have power added efficiencies of about 80%. but this efficiency drops quickly with increase in the operating frequency.

94. amplifiers are linear circuits, where the transistor is biased to conduct over the entire range of the input signal cycle.
a. class a amplifiers

b. class b amplifiers

c. class c amplifiers

d. none of the mentioned

Answer:
a. class a amplifiers
Clarification: class a amplifiers are linear circuits, where the transistor is biased to conduct over the entire range of the input signal cycle. because of this, class a amplifiers theoretically have a maximum efficiency of 50%.

95. A class B amplifier consists of transistors in order to conduct the input signal over the entire cycle.
a. 1

b. 2

c. 4

d. 6

Answer:
b. 2
Clarification: class b amplifier is biased to conduct only during one-half of the input signal cycle. 2 complementary transistors are operated in a class b push pull amplifier to provide amplification over the entire cycle.

96. Power amplifiers in the increasing order of efficiency is:
a. class a, b, c

b. class c, a, b

c. class b, a, c

d. efficiency of all the 3 amplifiers is the same

Answer:
a. class a, b, c
Clarification: class a amplifiers have an efficiency of about 50%. class b amplifiers have an efficiency of about 78%, class c amplifiers can achieve efficiencies up to 100%. in the increasing order of efficiency, c

97. Behavior of a transistor in power amplifiers is unpredictable at all input signal levels.
a. true

b. false

Answer:
b. false
Clarification: a transistor behaves linearly for signal powers below 1db compression point and so, the small –signal scattering parameters should not depend either on the input power level or the output termination impedance.

98. If the output power of an amplifier is 10 V, and the input power supplied to the amplifier is 0.229 V given that the DC voltage used is
a. 25%

b. 50%

c. 75%

d. 35%

Answer:
a. 25%
Clarification: efficiency of a power amplifier is (pout- pin)/ pdc substituting the given values in the above expression, efficiency of the power amplifier is 25%.

99. If a power amplifier has an output power of 10 W, and an amplifier gain of 16.4 dB, then the input drive power is:
a. 400 mw

b. 225 mw

c. 229 mw

d. 240 mw

Answer:
c. 229 mw
Clarification: input drive power required to get an output of 10 w is pout (dbm)- g (db). g is the gain of the amplifier. substituting the given values in the above equation, 229 mw.

100. GaAs is used in the fabrication of GUNN diodes because:
a. gaas is cost effective

b. it less temperature sensitive

c. it has low conduction band electrons

d. less forbidden energy gap

Answer:
d. less forbidden energy gap
Clarification: in gaas, the conduction band lies directly above the top of the valence band. the lowest energy conduction band in gaas is called as primary valley. gaas consists of six secondary valleys. the bottom of one of the secondary valley is at an energy difference of 0.35 ev with the bottom of the primary valley in conduction band.

101. In a GaAs n-type specimen, the current generated is constant irrespective of the electric filed applied to the specimen.
a. true

b. false

Answer:
b. false
Clarification: in a gaas n-type specimen, when the electric field applied reaches a threshold value of eth, the current in the specimen becomes suddenly oscillatory and with respect to time and these oscillations are in the microwave frequency range. this effect is called gunn effect.

102. When the electric field applied to GaAs specimen is less than the threshold electric field, the current in the material:
a. increases linearly

b. decreases linearly

c. increases exponentially

d. decreases exponentially

Answer:
a. increases linearly
Clarification: when the electric field applied is less than the threshold value of electric field, the electrons jump from the valence band to the primary valley of the conduction band and current increases linearly with electric field.

103. GaAs is used in fabricating Gunn diode. Gunn diode is:
a. bulk device

b. sliced device

c. made of different type of semiconductor layers

d. none of the mentioned

Answer:
a. bulk device
Clarification: a gunn diode is a bulk device, that is, it does not contain any junction but it is a slice of n-type gaas. p- type gaas does not exhibit gunn effect. hence it is a reversible and can be operated in both directions.

104. The electrodes of a Gunn diode are made of:
a. molybdenum

b. gaas

c. gold

d. copper

Answer:
a. molybdenum
Clarification: gunn diode is grown epitaxially onto a gold or copper plated molybdenum electrode, out of gallium arsenide doped with silicon, tellurium or selenium to make it n-type.

105. When either a voltage or current is applied to the terminals of bulk solid state compound GaAs, a differential is developed in that bulk device.
a. negative resistance

b. positive resistance

c. negative voltage

d. none of the mentioned

Answer:
a. negative resistance
Clarification: when either a voltage or current is applied to the terminals of a sample of bulk solid state compound formed by group 5 and 3 elements of periodic table, a differential resistance is developed in the bulk device. this fundamental concept is called rwh theory.

106. The number of modes of operation for n type GaAs is:
a. two

b. three

c. four

d. five

Answer:
c. four
Clarification: n-type gaas used for fabricating gunn diode has four modes of operation. they are gunn oscillation mode, limited space charge accumulation mode, and stable amplification mode bias circuit oscillation mode.

107. The free electron concentration in N-type GaAs is controlled by:
a. effective doping

b. bias voltage

c. drive current

d. none of the mentioned

Answer:
a. effective doping
Clarification: the free electron concentration in n-type gaas is controlled through effective doping so that they range from 1014 to 1017 per cc at room temperature. the typical specimen of n-type gaas has the dimensions 150 µm by 150 µm.

108. The modes of operation of a Gunn diode are illustrated in a plot of voltage applied to the Gunn diode v/s frequency of operation of Gunn diode.
a. true

b. false

Answer:
b. false
Clarification: a graph of plot of product of frequency and the length of the device plotted along y-axis versus the product of doping concentration and length along x- axis. these are the parameters on which the four modes of operation of gunn diode are explained.

109. The mode of operation in which the Gunn diode is not stable is:
a. gunn oscillation mode

b. limited space charge accumulation mode

c. stable amplification mode

d. bias circuit oscillation mode

Answer:
a. gunn oscillation mode
Clarification: in gunn oscillation mode, the device is unstable due to the formation of accumulation layer and field domain. this high field domain moves from cathode to anode.

110. The frequency of oscillation in Gunn diode is given by:
a. vdom/ leff

b. leff/ vdom

c. leff/ wvdom

d. none of the mentioned

Answer:
a. vdom/ leff
Clarification: in gunn oscillation mode, the frequency of oscillation is given by vdom/ leff, where vdom is the domain velocity, leff is effective length that the domain moves from the time it is formed until the time a new domain is formed.

111. In Gunn diode oscillator, the Gunn diode is inserted into a waveguide cavity formed by a short circuit termination at one end
a. true

b. false

Answer:
a. true
Clarification: the gunn diode is mounted at the centre of the broad wall of a shorted waveguide since for the dominant te10 mode; the electric field is maximum at the centre.

112. In a Gunn diode oscillator, the electron drift velocity was found to be 107 cm/second and the effective length is 20 microns, then the intrinsic frequency is:
a. 5 ghz

b. 6 ghz

c. 4 ghz

d. 2 ghz

Answer:
a. 5 ghz
Clarification: the intrinsic frequency for a gunn oscillator is given by vd/l. here vd is the drift velocity and l is the effective length. substituting the given values in the above equation, intrinsic frequency is 5 ghz.

113. The material used to fabricate IMPATT diodes is GaAs since they have the highest efficiency in all aspects.
a. true

b. false

Answer:
b. false
Clarification: impatt diodes can be fabricated using silicon, germanium, gaas or indium phosphide. out of these materials, gaas have highest efficiency, low noise and high operating frequencies. but gaas has a major disadvantage of complex fabrication process and higher cost. so, gaas are not preferred over silicon and germanium.

114. 3 IMPATT DIODES, SCHOTTKY BARRIER DIODES, PIN DIODES
a. avalanche multiplication

b. break down of depletion region

c. high reverse saturation current

d. none of the mentioned

Answer:
a. avalanche multiplication
Clarification: a reverse bias voltage exceeding the breakdown voltage is applied to an impatt diode, a high electric field appears across the n+ p junction. this high field imparts sufficient energy to the holes and also to valence electrons to raise themselves to the conduction band. this results in avalanche multiplication of electron hole pair.

115. To prevent an IMPATT diode from burning, a constant bias source is used to maintain at safe limit.
a. average current

b. average voltage

c. average bias voltage

d. average resistance

Answer:
a. average current
Clarification: avalanche multiplication is a cumulative process resulting in rapid increase of carrier density. to prevent the diode from burning due to this increased carrier density, a constant bias source is used to maintain average current at safe limit.

116. The number of semiconductor layers in IMPATT diode is:
a. two

b. three

c. four

d. none of the mentioned

Answer:
c. four
Clarification: impatt diode consists of 4 layers according to the construction. it consists of a p+ region and n+ layers at the two ends. in between these layers, a p type layer and an intrinsic region is sandwiched.

117. The resonant frequency of an IMPATT diode is given by:
a. vd/2l

b. vd/l

c. vd/2πl

d. vdd/4πl

Answer:
a. vd/2l
Clarification: the resonant frequency of an impatt diode is given by the expression vd/2l. here vd is the carrier drift velocity; l is the length of the intrinsic region in the impatt diode.

118. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the drift time of the carrier is:
a. 10-11 seconds

b. 2×10-11 seconds

c. 2.5×10-11 seconds

d. none of the mentioned

Answer:
b. 2×10-11 seconds
Clarification: the drift time of the carrier is defined as the ratio of length of the intrinsic region to the carrier drift velocity.

119. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the nominal frequency of the diode is:
a. 12 ghz

b. 25 ghz

c. 30 ghz

d. 24 ghz

Answer:
b. 25 ghz
Clarification: nominal frequency is defined as the ratio of the carrier drift velocity to twice the length of the intrinsic region.

120. IMPATT diodes employ impact ionization technique which is a noisy mechanism of generating charge carriers.
a. true

b. false

Answer:
a. true
Clarification: impatt devices employ impact ionization techniques which is too noisy. hence in order to achieve low noise figure, impact ionization is avoided in baritt diodes. the minority injection is provided by punch through of the intermediate region.

121. An essential requirement for the BARITT diode is that the intermediate drift region be completely filled to cause the punch through to occur.
a. true

b. false

Answer:
b. false
Clarification: an essential requirement for the baritt diode is that the intermediate drift region be completely filled to cause the punch through to the emitter-base junction without causing avalanche breakdown of the base collector junction.

122. If the RMS peak current in an IMPATT diode is 700 mA and if DC input power is 6 watt, with the load resistance being equal to
a. 10.1 %

b. 10.21 %

c. 12 %

d. 15.2 %

Answer:
b. 10.21 %
Clarification: efficiency of impatt diode is defined as the ratio of output rms power to the input dc power. calculating the rms output power from the given rms current and substituting in the equation of efficiency, the efficiency is 10.21%.

123. If the critical field in a Gunn diode oscillator is 3.2 KV/cm and effective length is 20 microns, then the critical voltage is:
a. 3.2 v

b. 6.4 v

c. 2.4 v

d. 6.5 v

Answer:
b. 6.4 v
Clarification: critical voltage of a gunn diode oscillator is given by the expression lec where l is the effective length and ec is the critical field. substituting the given values in the above equation, critical voltage is 6.4 volts.

124. The production of power at higher frequencies is much simpler than production of power at low frequencies.
a. true

b. false

Answer:
b. false
Clarification: as frequency increases to the millimeter and sub millimeter ranges, it becomes increasingly more difficult to produce even moderate power with solid state devices, so microwave tubes become more useful at these higher frequencies.

125. Microwave tubes are power sources themselves at higher frequencies and can be used independently without any other devices.
a. true

b. false

Answer:
b. false
Clarification: microwave tubes are not actually sources by themselves, but are high power amplifiers. these tubes are in conjunction with low power sources and this

126. The klystron tube used in a klystron amplifier is a type beam amplifier.
a. linear beam

b. crossed field

c. parallel field

d. none of the mentioned

Answer:
a. linear beam
Clarification: in klystron amplifier, the electron beam passes through two or more resonant cavities. the first cavity accepts an rf input and modulates the electron beam by bunching it into high density and low density regions.

127. In crossed field tubes, the electron beam traverses the length of the tube and is parallel to the electric field.
a. true

b. false

Answer:
b. false
Clarification: in a crossed field or ‘m’ type tubes, the focusing field is perpendicular to the accelerating electric field. since the focusing field and accelerating fields are perpendicular to each other, they are called crossed field tubes.

128. is a single cavity klystron tube that operates as on oscillator by using a reflector electrode after the cavity.
a. backward wave oscillator

b. reflex klystron

c. travelling wave tube

d. magnetrons

Answer:
b. reflex klystron
Clarification: reflex klystron is a single cavity klystron tube that operates as on oscillator by using a reflector electrode after the cavity to provide positive feedback via the electron beam. it can be tuned by mechanically adjusting the cavity size.

129. A major disadvantage of klystron amplifier is:
a. low power gain

b. low bandwidth

c. high source power

d. design complexity

Answer:
b. low bandwidth
Clarification: klystron amplifier offers a very narrow operating bandwidth. this is overcome in travelling wave tube (twt).

130. In a oscillator, the RF wave travels along the helix from the collector towards the electron gun.
a. interaction oscillator

b. backward wave oscillator

c. magnetrons

d. none o the mentioned

Answer:
b. backward wave oscillator
Clarification: in a backward wave oscillator, the rf wave travels along the helix from the collector towards the electron gun. thus the signal for oscillation is provided by the bunched electron beam itself and oscillation occurs.

131. Magnetrons are microwave devices that offer very high efficiencies of about 80%.
a. true

b. false

Answer:
a. true
Clarification: magnetrons are capable of very high power outputs, on the order of several kilowatts, and with efficiencies of 80% or more. but disadvantage of magnetron is that they are very noisy and cannot maintain frequency or phase coherence when operated in pulse mode.

132. Klystron amplifiers have high noise output as compared to crossed field amplifiers.
a. true

b. false

Answer:
b. false
Clarification: crossed filed amplifiers have very good efficiencies – up to 80%, but the gain is limited to 10-15 db) in addition, the cfa has a noisier output than either a klystron amplifier or twt. its bandwidth can be up to 40%.

133. is a microwave device in which the frequency of operation is determined by the biasing field strength.
a. vtm

b. gyratron

c. helix bwo

d. none of the mentioned

Answer:
b. gyratron
Clarification: gyratron is a microwave device in which the frequency of operation is determined by the biasing field strength and the electron velocity, as opposed to the dimensions of the tube itself. this makes the gyrator especially useful for microwave frequencies.

134. 2 IMPEDANCE MATCHING
a. swr, first voltage minimum

b. swr, first voltage maximum

c. characteristic impedance, first voltage minimum

d. characteristic impedance, first voltage maximum

Answer:
a. swr, first voltage minimum
Clarification: with a slotted line, swr and the distance of the first voltage minimum from the load can be measured, from this data, load impedance can be found.

135. A modern device that replaces a slotted line is:
a. digital cro

b. generators

c. network analyzers

d. computers

Answer:
c. network analyzers
Clarification: although slotted lines used to be the principal way of measuring unknown impedance at microwave frequencies, they have largely been superseded by the modern network analyzer in terms of accuracy, versatility and convenience.

136. If SWR=1.5 with a wavelength of 4 cm and the distance between load and first minima is 1.48cm, then the reflection coefficient is:
a. 0.0126+j0.1996

b. 0.0128

c. 0.26+j0.16

d. none of the mentioned

Answer:
a. 0.0126+j0.1996
Clarification: ┌= (swr-1)/ (swr+1). substituting for swr in the above equation for reflection co-efficient, magnitude of the reflection co-efficient is 0.2. to find θ, θ=π+2βlmin, substituting lmin as 1.48cm, θ=86.4⁰. hence converting the polar form of the reflection co-efficient into rectangular co- ordinates, reflection co-efficient is 0.0126+j0.1996.

137. High gain is not achievable at microwave frequencies using BJT amplifiers because:
a. device construction

b. complex architecture

c. ports are not matched at high frequencies

d. none of the mentioned

Answer:
c. ports are not matched at high frequencies
Clarification: at higher frequencies, if higher bandwidth is desired, a compromise on maximum achievable gain is made. but at these higher frequencies, the ports of the amplifier are not matched to 50 Ω.

138. To flatten the gain response of a transistor:
a. biasing current has to be increased

b. input signal level has to increased

c. increase the operational bandwidth

d. give negative feedback to the amplifier

Answer:
d. give negative feedback to the amplifier
Clarification: negative feedback can be used to increase the gain response of the transistor, improve the input and output match, and increase the stability of the device.

139. In conventional amplifiers, a flat gain response is achieved at the cost of reduced gain. But this drawback can be overcome by using:
a. balanced amplifiers

b. distributed amplifiers

c. differential amplifiers

d. none of the mentioned

Answer:
a. balanced amplifiers
Clarification: in conventional amplifiers, a flat gain response is achieved at the cost of reduced gain. but this drawback can be overcome by using balanced amplifiers. this is overcome by using two 900 couplers to cancel input and output reflections from two identical amplifiers.

140. Bandwidth of balanced amplifier can be an octave or more, but is limited by the bandwidth of the coupler.
a. true

b. false

Answer:
a. true
Clarification: in order to achieve flat gain response, balanced amplifiers use couplers to minimize reflections. but this in turn reduces the bandwidth of the amplifier to the coupler bandwidth.

141. Coupler that is mostly used in balanced amplifiers to achieve the required performance is:
a. branch line coupler

b. wilkinson coupler

c. lange coupler

d. waveguide coupler

Answer:
c. lange coupler
Clarification: lange couplers are broadband couplers and are compact in size. since the bandwidth of a balanced amplifiers depends on the bandwidth of the coupler used. lange coupler is thus preferred over couplers.

142. Distributed amplifiers offer very high
a. gain

b. bandwidth

c. attenuation

d. none of the mentioned

Answer:
b. bandwidth
Clarification: distributed amplifiers offer very high bandwidth of about 10 decade. but higher gain cannot be achieved using distributed amplifiers and matching at the ports is very important to achieve higher bandwidth.

143. In distributed amplifiers, all the FET stages in the amplifier are connected in series to one another.
a. true

b. false

Answer:
b. false
Clarification: in distributed amplifiers, cascade of n identical fets have their gates connected to a transmission line having a characteristic impedance of zg with a spacing of lg while the drains are connected to a transmission line of characteristic impedance zd, with a spacing ld.

144. uses balanced input and output, meaning that there are 2 signal lines, with opposite polarity at each port.
a. differential amplifier

b. distributed amplifier

c. balanced amplifier

d. none of the mentioned

Answer:
a. differential amplifier
Clarification: differential amplifier uses balanced input and outputs, meaning that there are 2 signal lines, with opposite polarity at each port. it has two input ports and one output port. the difference of the 2 input signals is amplified.

145. A major advantage of differential amplifiers is:
a. high gain

b. low input impedance

c. higher output voltage swing

d. none of the mentioned

Answer:
c. higher output voltage swing
Clarification: differential amplifiers can provide higher voltage swings that are approximately double that obtained with single ended amplifier.

146. Along with a differential amplifier, 1800 hybrid is used both at the input and output.
a. true

b. false

Answer:
a. true
Clarification: a differential amplifier can be constructed using two single-ended amplifiers

147. is a non linear circuit that converts DC power to an AC waveform of desired frequency based on the oscillator design.
a. attenuator

b. amplifier

c. oscillator

d. none of the mentioned

Answer:
c. oscillator
Clarification: oscillator is a non linear circuit that converts dc power to an ac waveform. most rc oscillators provide sinusoidal outputs, which minimizes undesired harmonics and noise sidebands.

148. The transfer function of an RF oscillator is given by:
a. a/ (1-ah (ω))

b. a/ (1+ah (ω))

c. a/ (-1+ah (ω))

d. 1/ (1-ah (ω))

Answer:
a. a/ (1-ah (ω))
Clarification: transfer function of an rf oscillator is given by a/ (1-ah (ω)). here, a is the gain of the transistor multiplier used.

149. The criterion on which oscillations are produced in the oscillator circuit is called:
a. shannon’s criteria

b. barkhausen criteria

c. colpitts criteria

d. none of the mentioned

Answer:
b. barkhausen criteria
Clarification: when the condition 1-ah (ω)

150. The necessary condition for oscillation in a Colpitts oscillator is:
a. c2/c1=gm/gi

b. c1/c2=gm/gi

c. c2/c1= gm*gi

d. none of the mentioned

Answer:
a. c2/c1=gm/gi
Clarification: the condition for sustained oscillation in a colpitts oscillator is c2/c1 = gm/gi. here c1 and c2 are the capacitance in the feedback network, gm is the transconductance of the transistor and gi is the input admittance.

151. Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10µH. then the values of the capacitors in the feedback section is:
a. 100 pf, 100 pf

b. 100 pf, 50 pf

c. 70 pf, 130 pf

d. 80 pf, 60 pf

Answer:
a. 100 pf, 100 pf
Clarification: the equivalent value of series combination of the capacitors is given by 1/ ω2l. this gives the equivalent capacitance value of 200 pf. c1c2/ (c1+c2) =200 pf. c1

152. An inductor is operating at frequency of 50 MHz. Its inductance is 0.1 µH, and then the series resistance associated with the inductor is: (Qo=100)
a. 0.31 Ω

b. 1.32 Ω

c. 1 Ω

d. 1.561 Ω

Answer:
a. 0.31 Ω
Clarification: series resistance associated with an inductor is given by ωl/qₒ.

153. Hartley oscillator has inductance values of 12 mH and 4 mH in the feedback section and a capacitor of 4 nF. Then the resonant frequency of the circuit is:
a. 19.89 khz

b. 25 khz

c. 45 khz

d. 12 khz

Answer:
a. 19.89 khz
Clarification: resonant frequency of hartley oscillator is given by 1/ 2π√(c1 (l1 + l2)). substituting the given values in the above equation, cut-off frequency is 19.89 khz.

154. Colpitts oscillator in the feedback section has an inductance of 4 mH and capacitors of 12 nH and 4 nH. Then the resonant frequency of Colpitts oscillator is:
a. 50.4 khz

b. 35.1 khz

c. 45.9 khz

d. none of the mentioned

Answer:
c. 45.9 khz
Clarification: resonant frequency of colpitts oscillator is given by 1/2π√lcₒ, where c0 is the equivalent capacitance given by c1c2/ (c1+c2). substituting and solving the equation, resonant frequency is 45.9 khz.

155. For Colpitts oscillator, the capacitors C1 and C2 in the feedback network are 1 µF and 25 µF respectively. Then the β value of the transistor is:
a. 35

b. 000.76

c. 25

d. 0.0025

Answer:
c. 25
Clarification: β for a transistor is defined as the ratio of transconductance of the transistor to the input admittance, which is equal to the ratio of c2/c1. substituting the given values, β of the transistor is 25.

156. Amplifier efficiency is the ratio of RF output power to DC input power. This parameter determines the performance of an amplifier.
a. true

b. false

Answer:
a. true
Clarification: power amplifier is the primary consumer of dc power in most hand-held wireless devices, so amplifier efficiency is an important consideration. amplifier efficiency is the ratio of rf output power to dc input power.

157. Behavior of a transistor in power amplifiers is unpredictable at all input signal levels.
a. true

b. false

Answer:
b. false
Clarification: a transistor behaves linearly for signal powers below 1db compression point and so, the small –signal scattering

158. is defined as the ratio of desired signal power to undesired noise power.
a. signal to noise ratio

b. noise to signal ratio

c. noise figure

d. noise temperature

Answer:
a. signal to noise ratio
Clarification: snr is defined as the ratio of desired signal power to undesired noise

159. is defined as the ratio of input signal to noise ratio to the output signal to noise ratio.
a. noise figure

b. noise temperature

c. snro

d. none of the mentioned

Answer:
a. noise figure
Clarification: noise figure is defined as the ratio of input signal to noise ratio to the output signal to noise ratio of a system or a receiver. snri is the signal to noise ratio measured at the input terminals of the device. snr0 is the output signal to noise ratio measured at the output terminals of the device.

160. The equivalent noise temperature of a network given the noise figure of the network or system is:
a. t0(f-1)

b. t0(f+1)

c. t0(f)

d. t0/f

Answer:
a. t0(f-1)
Clarification: the equivalent noise temperature of a network given the noise figure of the network or system is given by t0(f-1). in this expression, f is the noise figure of the system. t0 has the value 290 k. t0 is the standard temperature considered.

161. Noise figure can be defined for any microwave network irrespective of any other constraints.
a. true

b. false

c. topic 5.6 low noise amplifier design

Answer:
b. false
Clarification: noise figure is defined only for a matched input source and for a noise source equivalent to a matched load at a temperature t0= 290 k. noise figure and noise temperature are interchangeable noise properties.

162. Expression for noise of a two port network considering the noise due to transmission line and other lossy components is:
a. gktb + gnadded

b. gktb

c. gnadded

d. none of the mentioned

Answer:
a. gktb + gnadded
Clarification: expression for noise of a two port network considering the noise due to transmission line and other lossy components is gktb + gnadded. here, g is the gain of the system. nadded is the noise generated by the transmission line, as if it appeared at the input terminals of the line.

163. Noise equivalent temperature of a 2 stage cascade network is given by:
a. te1 + te2/ g1

b. te1 + te1

c. te1 / te1

d. none of the mentioned

Answer:
a. te1 + te2/ g1
Clarification: noise equivalent temperature of a 2 stage cascade network is given by te1

164. For a Wilkinson power divider of insertion loss L and the coupler is matched to the external circuitry, and then the gain of the coupler in terms of insertion loss is:
a. 2l

b. 1/2l

c. l

d. 1/l

Answer:
b. 1/2l
Clarification: to evaluate the noise figure of the coupler, third port is terminated with known impedance. then the coupler becomes a two port device. since the coupler is matched, Гs=0 and Гout=s22=0. so the available gain is │s21│2. this is equal to 1/2l from the available data.

165. Noise equivalent temperature of Wilkinson coupler having a gain of 1/2L is given as:
a. t (2l-1)

b. t (2l+1)

c. t (2l*1)

d. t / (2l-1)

Answer:
a. t (2l-1)
Clarification: noise equivalent temperature of the wilkinson coupler is found using the relation

166. Expression for over all noise figure of a mismatched amplifier is:
a. 1+ (f-1)/ (1 -│Г│2)

b. 1

c. 1+ (f-1)

d. (f-1)/ (1 -│Г│2)

Answer:
a. 1+ (f-1)/ (1 -│Г│2)
Clarification: the overall noise figure of a

167. One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:
a. positive feedback is to be achieved

b. negative feedback is to be achieved

c. 1800 phase shift is required between the transistor input and output.

d. none of the mentioned

Answer:
c. 1800 phase shift is required between the transistor input and output.
Clarification: in an oscillator a total of 3600 of phase shift is to be achieved in the entire circuit to produce oscillations. the transistor used in the oscillator circuit must produce a phase shift of 1800 to achieve stable oscillations. hence this condition has to be satisfied by the oscillator.

168. In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.
a. true

b. false

Answer:
b. false
Clarification: if the resonant feedback circuit has a high q, so that there is random phase shift with frequency, the oscillator will have good frequency stability.

169. Quartz crystal and tourmaline used in oscillators work on the principle of:
a. photo electric effect

b. piezo electric effect

c. raman effect

d. black body radiation

Answer:
b. piezo electric effect
Clarification: quartz crystals work on the principle of piezo electric effect. when electrical energy is applied to these crystals, they vibrate in a direction perpendicular to the application of energy producing oscillations.

170. A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.
a. true

b. false

Answer:
b. false
Clarification: a quartz crystal has an equivalent circuit such that a series lcr network is in parallel with a capacitor. a quartz crystal thus has both series and parallel resonant frequencies.

171. In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:
a. capacitive

b. inductive

c. both capacitive and inductive

d. none of the mentioned

Answer:
b. inductive
Clarification: in the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is inductive. in this region between the series and parallel and series resonant frequencies, the operating point of the crystal is fixed and hence can be used as part of other circuits.

172. In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:
a. 0.25 mhz

b. 2.5 mhz

c. 25 mhz

d. 5 mhz

Answer:
a. 0.25 mhz
Clarification: the series resonant frequency of a crystal oscillator is given by 1/√lc. substituting the given values of l and c in the expression, the series resonant frequency is 0.25 mhz.

173. Parallel resonant frequency of quartz crystal is given by:
a. 1/ √(lcₒc/(cₒ+c))

b. 1/√lc

c. 1/√lcₒ

d. 1/ √(l(cₒ+c) )

Answer:
a. 1/ √(lcₒc/(cₒ+c))
Clarification: parallel resonant frequency of an oscillator is given by√(lcₒc/(cₒ+c)).

174. The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:
a. 3 mhz

b. 0.3 mhz

c. 6 mhz

d. 9 mhz

Answer:
a. 3 mhz
Clarification: the parallel resonant frequency of a crystal oscillator is given by 1/

175. In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.
a. true

b. false

Answer:
a. true
Clarification: in microwave oscillator, for a current to flow in the circuit the negative impedance of the device must be matched with positive impedance. this results in current being non-zero and generates oscillation.

176. Any device with negative impedance as its characteristic property can be called:
a. energy source

b. energy sink

c. oscillator

d. none of the mentioned

Answer:
a. energy source
Clarification: a positive resistance implies energy dissipation while a negative resistance implies an energy source. the negative resistance device used in the microwave oscillator, thus acts as a source. the condition xin+ xl=0 controls the frequency of oscillation. xin is the impedance of the negative resistance device.

177. In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.
a. true

b. false

Answer:
b. false
Clarification: the condition for steady state oscillation in a microwave oscillator is zin=- zl. since this condition is satisfied in the above case, steady state oscillation is achieved.

178. For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:
a. Гin=Гl

b. Гin=-Гl

c. Гin=1/Гl

d. none of the mentioned

Answer:
c. Гin=1/Гl
Clarification: the condition for steady state oscillation to be achieved in terms of reflection coefficient is Гin=1/Гl. here Гin is the reflection coefficient towards the reflection coefficient device and Гl is the reflection coefficient towards the load.

179. To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.
a. true

b. false

Answer:
b. false
Clarification: the condition zin + zl=0 is only a necessary condition for stable oscillation and not sufficient. stability requires that any perturbation in current or frequency is damped out, allowing the oscillator to return to its original state.

180. In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.
a. true

b. false

Answer:
b. false
Clarification: in a transistor oscillator, a negative resistance one port network is created by terminating a potentially unstable transistor with impedance designed to drive the device in an unstable region.

181. In transistor oscillators, FET and BJT are used. Instability is achieved by:
a. giving a negative feedback

b. giving a positive feedback

c. using a tank circuit

d. none of the mentioned

Answer:
b. giving a positive feedback
Clarification: oscillators require a device that has high instability. to achieve this condition, transistors are used with a positive feedback to increase instability.

Antennas & Microwave Engineering Objective Questions with Answers Pdf Download

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