Category: Microwave Engineering Objective Questions

250+ TOP MCQs on Antenna Radiation and Answers

Microwave Engineering Multiple Choice Questions on “Antenna Radiation”.

1. An antenna source that radiates energy uniformly in all the directions is called:
A. Isotropic source
B. Anisotropic source
C. Point source
D. None of the mentioned
Answer: A
Clarification: Isotropic source radiates energy in all the direction uniformly. For such a source, the radial component Sr of the pointing vector is independent of θ and φ. The three dimensional power pattern of n isotropic source is a sphere.

2. Antennas that radiate energy only in a specified are called anisotropic antennas.
A. True
B. False
Answer: A
Clarification: All physically realizable, simplest antennas also have directional properties. That is, they radiate energy in one direction than in any other direction. Such sources are called anisotropic point sources.

3. The expression for pointing vector of an isotropic point source at a distance ‘r’ from the source is given by:
A. P/ 4πR2
B. P/4π
C. P/ 4πR
D. P×4πR2
Answer: A
Clarification: The pointing field vector for an isotropic source is given by the expression P/ 4πR2.P is the total power radiated y the source. As the distance of the point from the source increases, the magnitude of pointing vector decreases.

4. A source has a cosine radiation-intensity pattern given by U=UM cos (θ). The directivity of this source is:
A. 2
B. 4
C. 6
D. 8
Answer: B
Clarification: To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by an isotropic source gives the directivity. Following the above steps, the directivity of the given source is 4.

5. A source has a cosine power pattern that is bidirectional. Given that the directivity of a unidirectional source with cosine power pattern has a directivity of 4, then the directivity of the unidirectional source is:
A. 1
B. 2
C. 4
D. 8
Answer: B
Clarification: Given the directivity of unidirectional power pattern, the directivity of bidirectional power pattern is half of it. Hence the directivity of the source is 2.

6. A source has a radiation intensity pattern given by U=UM sin θ. The directivity of the source with this power pattern is:
A. 1
B. 1.27
C. 2.4
D. 3.4
Answer: B
Clarification: To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by an isotropic source gives the directivity. Following the above steps, the directivity of the given source is 1.27.

7. A source has a sine squared radiation intensity power pattern. The directivity of the given source is:
A. 1.5
B. 3
C. 2.5
D. 3.5
Answer: A
Clarification: To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by an isotropic source gives the directivity. Following the above steps, the directivity of the given source is 1.5.

8. A source with a unidirectional cosine squared radiation intensity pattern is given by UMcos2 (θ). The directivity of the given source is:
A. 6
B. 8
C. 2
D. 7
Answer: A
Clarification: To find the directivity of the given source, the power radiated by the given source is found out by the method of integration. Taking the ratio of the power radiated by the given source to the power radiated by anisotropic source gives the directivity. Following the above steps, the directivity of the given source is 6.

9. Considering distance as a parameter, two types of field zones can be defined around an antenna.
A. True
B. False
Answer: A
Clarification: Considering distance as a parameter, two types of field zones can be defined around an antennA. .The field near the antenna is called near field or Fresnel region and the other region is the far field that is also called as Fraunhofer region.

10. If the field strength at receiving antenna is 1 µV/m, and the effective aperture area is 0.4 m2 and the intrinsic impedance of the medium is 377 Ω, then the power received by the antenna is:
A. 1.06 pW
B. 1.06 fW
C. 2 µW
D. None of the mentioned
Answer: B
Clarification: The received power by the antenna is given by E2Ae/Zₒ. Substituting the known values in the above equation, the power received is 1.06×10-15 watts.


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250+ TOP MCQs on Smith Chart and Answers

Microwave Engineering Multiple Choice Questions on “Smith Chart”.

1. Smith chart is based on the polar plot of:
A. Reactance
B. Voltage
C. Current
D. Voltage reflection co-efficient
Answer: D
Clarification: let the reflection co-efficient be expressed in terms of magnitude and direction as ┌=|┌|ejθ. Magnitude is plotted as radius from the center of the chart, and the angle is measured in counter clockwise direction from the right hand side. Hence, smith chart is based on the polar pot of voltage reflection co-efficient.

2. Any passively realizable reflection coefficient can be plotted as a unique point on the smith chart. This statement implies that:
A. Reflection co-efficient less than or equal to 1 can be plotted
B. Reflection co-efficient greater than or equal to 1 can be plotted
C. Transmission co-efficient has to be less than or equal to one for the point to be located
D. T=Г+1
Answer: A
Clarification: Reflection co-efficient is defined as the ratio of reflected voltage /current to the incident voltage or current. Hence reflection co-efficient can never be greater than 1. Hence, only reflection co-efficient less than or equal to 1 can be plotted.

3. Reflection coefficient of a transmission line in its polar form can be represented as:
A. ┌=|┌|ejθ
B. ┌=|┌|ejθ-1
C. ┌=|┌|ejθ+1
D. ┌=|┌|ejθ+α
Answer: A
Clarification: Reflection c co-efficient is defined as the ratio of reflected voltage /current to the incident voltage or current. It is a complex value consisting of both real and imaginary parts. Converting it to polar form, it takes the form of ┌=|┌|ejθ, Consisting of both magnitude and phase θ.

4. If the characteristic impedance of a ƛ/2 transmission line is 50 Ω and reflection coefficient 0.3, then its input impedance
A. 26.92 Ω
B. 30 Ω
C. 40 Ω
D. 34.87 Ω
Answer: A
Clarification: Given the characteristic impedance and reflection coefficient of a transmission line, input impedance is given by Zₒ (1+Гe-2jβL)/ (1- Гe-2jβL). Substituting the given values, the input impedance of the line is 26.92 Ω

5. If the normalized input impedance of a transmission line is 0.5 Ω, then he reflection coefficient of a ƛ/2 transmission line is
A. 0.3334
B. 0.5
C. 0.6667
D. 1
Answer: A
Clarification: Given the characteristic impedance and reflection coefficient of a transmission line, input impedance is given by Zₒ (1+Гe-2jβL)/ (1- Гe-2jβL). Substituting the given values in the above equation, reflection coefficient is 0.3334.

6. If the input impedance of a ƛ/2 transmission line is 100 Ω with a voltage reflection coefficient of 0.344, then the characteristic impedance of the transmission line is:
A. 200 Ω
B. 100 Ω
C. 50 Ω
D. None of the mentioned
Answer: A
Clarification: Given the characteristic impedance and reflection coefficient of a transmission line, input impedance is given by Zₒ (1+Гe-2jβL)/ (1- Гe-2jβL). Substituting the given values in the above equation, characteristic impedance of the transmission line is 200 Ω.

7. Normalized impedance of 0.3+j0.4 lies in the:
A. Upper half of the impedance smith chart
B. Lower half of the impedance smith chart
C. Horizontal line of the chart
D. None of the mentioned
Answer: A
Clarification: In the impedance smith chart, the upper part of the smith chart refers to positive reactance or inductive reactance. Hence, the given point lies in the upper half of the smith chart corresponding to the intersection of circles r=0.3 and r=0.4

8. Normalized impedance of 1-j is:
A. In the upper half of the impedance smith chart
B. In the Lower half of the impedance smith chart
C. On the outer most circle of the smith chart.
D. On the horizontal line of the smith chart
Answer: B
Clarification: In the impedance smith chart, the lower half of the smith chart corresponds to negative reactance or capacitive reactance. Hence the given point lies in the lower half of the smith chart.

9. If a transmission line of a characteristic impedance 100 Ω is terminated with a load impedance of 300+j200 Ω, then the normalized load impedance is:
A. 1+j
B. 1-j
C. 3+2j
D. 2-3j
Answer: C
Clarification: Normalized load impedance is obtained by dividing the load impedance with the characteristic impedance of the transmission line. Dividing 300+200j from 100, we get 3+2j.

10. If the normalized load impedance of a transmission line is 0.3-j0.4 with a characteristic impedance of 50 Ω, then the load impedance is:
A. 15-j20
B. 15+j20
C. 1-j
D. 0.3-0.4j
Answer: A
Clarification: Load impedance is the product of characteristic impedance and normalized load impedance. Hence taking the product of characteristic impedance and load impedance, we get 15-j20Ω.

11. To get an admittance chart from an impedance chart:
A. Smith chart has to be rotated by 90⁰
B. Smith chart has to be rotated by 180⁰
C. Admittance chart cannot be obtained from the impedance chart anyway.
D. None of the mentioned
Answer: B
Clarification: Impedance and admittance parameters, both are a reciprocal of one another. Hence one chart can be obtained from the other chart. By rotating the impedance smith chart by an angle of 180⁰, admittance chart is obtained.


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250+ TOP MCQs on Impedance Matching Using Slotted Lines and Answers

Microwave Engineering Interview Questions and Answers for freshers on “Impedance Matching Using Slotted Lines”.

1. 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
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.

2. A slotted line can be used to measure _____ and the distance of _____________ from the load.
A. SWR, first voltage minimum
B. SWR, first voltage maximum
C. characteristic impedance, first voltage minimum
D. characteristic impedance, first voltage maximum
Answer: A
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.

3. A modern device that replaces a slotted line is:
A. Digital CRO
B. generators
C. network analyzers
D. computers
Answer: C
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.

4. 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
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.

5. 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
Clarification: SWR= (1+┌)/ (1-┌). Where ┌ is the reflection co-efficient. Substituting for the reflection co-efficient in the equation, SWR is 2.3333.

6. Expression for ϴ means phase angle of the reflection co efficient r=|r|-e^jθ, the phase of the reflection co-efficient is:
A. θ=2π+2βLmin
B. θ=π+2βLmin
C. θ=π/2+2βLmin
D. θ=π+βLmin
Answer: B
Clarification: here, θ is the phase of the reflection co-efficient. Lmin is the distance from the load to the first minimum. Since voltage minima repeat every λ/2, any multiple of λ/2 can be added to Lmin .

7. 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
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.

8. 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
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.

9. If the characteristic impedance of a transmission line 50 Ω and reflection coefficient is 0.0126+j0.1996, then load impedance is:
A. 47.3+j19.7Ω
B. 4.7+j1.97Ω
C. 0.26+j0.16
D. data insufficient
Answer: a
Clarification: ZL=Z0 (1+┌)/ (1-┌). Substituting the given values of reflection co-efficient and characteristic impedance, ZL is 47.3+j19.7Ω .

10. If the normalized load impedance of a transmission line is 2, then the reflection co-efficient is:
A. 0.33334
B. 1.33334
C. 0
D. 1
Answer: A
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.


250+ TOP MCQs on Wilkinson Power Dividers and Answers

Microwave Engineering Multiple Choice Questions on “Wilkinson Power Dividers”.

1. A major disadvantage of the lossless T-junction power divider is:
A. Not matched at all the ports
B. Low power output
C. Complex construction
D. None of the mentioned
Answer: A
Clarification: A T-junction hybrid cannot be matched at all the ports if the power divider is lossless. It can be matched only at 2 ports. This is one of the major disadvantages when they are to be used along with other microwave devices.

2. The Wilkinson power divider is a:
A. 2 port network
B. 3 port network
C. 4 port network
D. None of the mentioned
Answer: B
Clarification: Wilkinson power divider is a 3 port network; if it is used as a divider it has one input port and 2 output ports. If it is used as coupler, it has two input port and one output port.

3. Wilkinson power divider is an equal split power divider.
A. True
B. False
Answer: B
Clarification: Wilkinson power divider can be used to divide power in any ratio, but the most commonly used configuration is the equal split power divider.

4. If 10 watt is applied to the input port of a standard Wilkinson divider, then the sum of the power measured at the two output ports of the Wilkinson coupler is
A. 5 watt
B. 10 watt
C. 7.07 watt
D. 8 watt
Answer: C
Clarification: For a standard Wilkinson coupler, the output power is 3 dB less than the total input power in decibels. That is, 70.7% of the total input power is delivered to the output port.

5. The analysis of Wilkinson coupler is done using:
A. Even-odd mode analysis
B. Symmetry
C. S matrix approach
D. None of the mentioned
Answer: A
Clarification: Even-odd mode analysis is one of the simplest methods of analysis for Wilkinson coupler. This involves normalizing all impedances with the characteristic impedance of the transmission line used and carrying out some analysis.

6. A Wilkinson coupler designed can be operated at any frequency.
A. True
B. False
Answer: B
Clarification: The length of the branches of a Wilkinson coupler is all wavelengths dependent and hence Wilkinson coupler designed to operate at one frequency cannot be used to operate at another frequency.

7. For an equal-split Wilkinson power divider of 50Ω system impedance, the characteristic impedance of quarter wave transmission line used is:
A. 70.7 Ω
B. 50 Ω
C. 100 Ω
D. None of the mentioned
Answer: A
Clarification: The characteristic impedance of a Z Ω system is given by √2*Z. hence, the characteristic impedance of 50Ω system is 70.7 Ω.

8. The plot of frequency v/s S11 parameter of a Wilkinson coupler has a dip at the frequency at which it is designed to operate.
A. True
B. False
Answer: A
Clarification: S11 parameter signifies the fraction of the power reflected back to port 1 when power is applied to port 1 of the coupler. Since the ports are matched at the frequency of design S11 is minimum and the curve has a dip.

9. The plot of S23 v/s frequency has the same curve as that of S11 v/s frequency.
A. True
B. False
Answer: A
Clarification: When input is applied to port 1, output is measured at port 2 and port 3. S23 signifies the output at port 3 due to port 2 when input is applied at port 1. This parameter is minimum at the designed frequency.

10. S12 curve of a Wilkinson coupler when plotted versus frequency is a line passing through origin.
A. True
B. False
Answer: B
Clarification: S12 gives the ratio of power at input port P1 to the power measured at port 2. Since the output power remains constant over a wide range of frequencies for a given input applied. Hence S11 is a curve parallel to X axis.


Microwave Engineering,

250+ TOP MCQs on IMPATT and BARITT Diodes and Answers

Microwave Engineering Multiple Choice Questions on “IMPATT and BARITT Diodes”.

1. The material used to fabricate IMPATT diodes is GaAs since they have the highest efficiency in all aspects.
A. true
B. false
Answer: B
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.

2. When a reverse bias voltage exceeding the breakdown voltage is applied to an IMPATT diode, it results in:
A. avalanche multiplication
B. break down of depletion region
C. high reverse saturation current
D. none of the mentioned
Answer: A
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.

3. 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
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.

4. The number of semiconductor layers in IMPATT diode is:
A. two
B. three
C. four
D. none of the mentioned
Answer: C
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.

5. The resonant frequency of an IMPATT diode is given by:
A. Vd/2l
B. Vd/l
C. Vd/2πl
D. Vdd/4πl
Answer: A
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.

6. 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
Clarification: The drift time of the carrier is defined as the ratio of length of the intrinsic region to the carrier drift velocity. Substituting the given values in this relation, the drift time of the carrier is 2×10-11 seconds.

7. 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
Clarification: Nominal frequency is defined as the ratio of the carrier drift velocity to twice the length of the intrinsic region. Substituting the given values in the above equation, the nominal frequency is 25 GHz.

8. IMPATT diodes employ impact ionization technique which is a noisy mechanism of generating charge carriers.
A. true
B. false
Answer: A
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.

9. 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
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.

10. 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 2.5 Ω, the efficiency of the diode is:
A. 10.1 %
B. 10.21 %
C. 12 %
D. 15.2 %
Answer: B
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%.

11. 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
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.


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250+ TOP MCQs on Microwave Oscillators and Answers

Microwave Engineering Multiple Choice Questions on “Microwave Oscillators”.

1. In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.
A. True
B. False
Answer: A
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.

2. 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
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.

3. 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
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.

4. 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
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.

5. A one port oscillator uses a negative resistance diode having Гin=0.9575+j0.8034 (Z0=50Ω) at its desired frequency point. Then the input impedance of the diode is:
A. -44+j123
B. 50+j100
C. -44+j145
D. None of the mentioned
Answer: A
Clarification: The input impedance of the diode given reflection coefficient and characteristic impedance is Z0 (1+Гin)/ (1-Гin). Substituting in the given equation, the input impedance is -44 +j123 Ω.

6. If the input impedance of a diode used in the microwave oscillator is 45-j23 Ω, then the load impedance is to achieve stable oscillation is:
A. 45-j23 Ω
B. -45+j23 Ω
C. 50 Ω
D. 23-j45 Ω
Answer: B
Clarification: The condition for stabilized oscillation is Zin=-ZL. According to this equation, the load impedance required for stabilized oscillation is – (45-j23) Ω. The load impedance is thus -45+j23 Ω.

7. 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
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.

8. In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.
A. True
B. False
Answer: B
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.

9. 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
Clarification: Oscillators require a device that has high instability. To achieve this condition, transistors are used with a positive feedback to increase instability.

10. In a transistor amplifier, if the input impedance is -84-j1.9 Ω, then the terminating impedance required to create enough instability is:
A. -84-j1.9 Ω
B. 28+j1.9 Ω
C. – (28+j1.9) Ω
D. None of the mentioned
Answer: B
Clarification: Relation between terminating impedance and input impedance is Zs=-Rin/3. Zs is the terminating impedance. Substituting in the given equation, the terminated impedance is 28+j1.9 Ω.


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