Category: Microwave Engineering Objective Questions

250+ TOP MCQs on Two Port Power Gains and Answers

Microwave Engineering Multiple Choice Questions on “Two Port Power Gains”.

1. The power gain G of a two port network is independent of the source impedance of the two port network.
A. True
B. False
Answer: A
Clarification: Power gain G is the ratio of power dissipated in the load ZL to the power delivered to the input of the two port network. This gain is independent of ZS although the characteristic of some active devices is dependent on ZS.

2. __________ is defined as the ratio of power available from the two port network to the power available from the source.
A. Transducer power gain
B. Available power gain
C. Power gain
D. None of the mentioned
Answer: B
Clarification: Available power gain is defined as the ratio of power available from the two port network to the power available from the source. This assumes conjugate matching of both source and the load and depends on ZS, not ZL.

3. Transducer power gain of a two port network is dependent on :
A. ZS and ZL
B. ZS
C. ZL
D. Independent of both the impedances
Answer: A
Clarification: Transducer power gain of a two port network is the ratio of the power delivered to the load to the power available from the source. This depends on both ZS and ZL.

4. For a two port network the voltage reflection coefficient seen looking towards the load, ГS is:
A. (ZS –Z0)/ (ZS –Z0)
B. (ZS +Z0)/ (Z0 – Z0)
C. ZS / (ZS –Z0)
D. Z0/ (ZS –Z0)
Answer: A
Clarification: For a two port network, the reflection coefficient ГS seen looking towards the load is (ZS –Z0)/ (ZS –Z0). Here ZS is the input impedance of the transmission line and Z0 is the characteristic impedance of the transmission line.

5. In a two port network, the source impedance was measured to be 25 Ω and the characteristic impedance of the transmission line was measured to be 50 Ω. Then the reflection coefficient at the source end is:
A. -0.33333
B. -0.1111
C. 0.678
D. 0.2345
Answer: A
Clarification: For a two port network, the reflection coefficient ГS seen looking towards the load is (ZS –Z0)/ (ZS –Z0). Substituting the given values in the above equation, reflection coefficient at the source end is -0.3333.

6. For a unilateral transistor, the S parameter that is zero is:
A. S11
B. S12
C. S21
D. S22
Answer: B
Clarification: In a unilateral transistor power flow occurs only in one direction and hence S12 is sufficiently small and can be ignored. Also for a unilateral transistor the reflection coefficients reduce to Гin=S11 and Гout=S22.

7. Gain of an amplifier is independent of the operating frequency.
A. True
B. False
Answer: B
Clarification: Gain of an amplifier depends on the operating frequency. Gain of a conjugate matched FET amplifier drops off as 1/f2 or 6dB per octave.

8. Gain of a conjugate matched FET amplifier is given by the relation:
A. Rds (fT)2/ 4Ri (f)2
B. 4Ri (f)2/Rds (fT)2
C. Rds/ Ri
D. None of the mentioned
Answer: A
Clarification: Gain of FET amplifier is given by the relation Rds (fT)2/ 4Ri (f)2. Gain depends on the drain to source resistance, input resistance and also on the frequency of operation of the amplifier.

9. When both input and output of an amplifier are matched to zero reflection (in contrast to conjugate matching), the transducer power gain is:
A. │S21│2
B. │S22│2
C. │S12│2
D. |S11│2
Answer: A
Clarification: When both input and output of an amplifier are matched to zero reflection, ГL=0 and ГS=0. This reduces the complex transducer gain equation to the s parameter of the amplifier S21. S21 signifies the power at port 2 due to input applied at port 1.

10. If the load impedance of a two port network is 40 Ω and the characteristic impedance is 50 Ω, then the reflection coefficient of the two port network at the load end is:
A. -0.111
B. -0.333
C. -0.987
D. None of the mentioned
Answer: A
Clarification: Reflection coefficient at the load end of a two port network is given by the ratio (ZL-Z0)/ (ZL+Z0). ZL is the load impedance and Z0 is the characteristic impedance. Substituting, reflection at load end is -0.1111.


all areas of Microwave Engineering,

250+ TOP MCQs on Noise Characteristics of Receivers and Answers

Microwave Engineering Multiple Choice Questions on “Noise Characteristics of Receivers”.

1. The noise power will determine the maximum detectable signal level for a receiver.
A. True
B. False
Answer: B
Clarification: The noise power will determine the minimum detectable signal level of the receiver for a given transmitter power, maximum range of a communication link. There is a limit on the maximum noise that can be associated with a signal in spite of which the signal can be recovered from the noise.

2. Equivalent noise temperature of a transmission line connecting the antenna to the receiver is:
A. TP (LP-1)
B. TP (LP + 1)
C. TP/ (LP-1)
D. TP / (LP + 1)
Answer: A
Clarification: The transmission line connecting the antenna to the receiver has a loss of LT and is at a physical temperature TP. its noise equivalent temperature is given by TP (LP-1).

3. In a receiver, if the noise figure of the mixer stage in the receiver is 7 dB, then the equivalent noise temperature is given that the receiver is operating at 290 K:
A. 1163 K
B. 1789 K
C. 1000 K
D. 1234 K
Answer: A
Clarification: Equivalent noise temperature for a given noise figure is given by To (FM-1). FM is the noise figure in dB. Substituting the given values for noise figure and temperature, noise equivalent temperature is 1163 K.

4. If a transmission line connecting the antennas to the receiver has a loss of 1.5 dB, given the physical temperature is 270C, noise equivalent temperature is:
A. 123 K
B. 145 K
C. 345 K
D. 234 K
Answer: A
Clarification: The noise equivalent temperature of the transmission line is given by TP(LP-1). Converting the value from dB scale and substituting, noise equivalent temperature is 123 K.

5. Given that the antenna efficiency is 0.9, equivalent brightness temperature is 200 K; physical temperature is 300 K, noise temperature of an antenna is:
A. 220 K
B. 210 K
C. 240 K
D. None of the mentioned
Answer: B
Clarification: Noise temperature of an antenna is given by rad Tb + (1- raD. TP. Tb is the equivalent brightness temperature and TP is the physical temperature. Substituting the given values, noise temperature of the antenna is 210 K.

6. If a receiver is operating at a bandwidth of 1 MHz and has antenna noise temperature of 210 K, then the input noise power is:
A. -90 dBm
B. -115 dBm
C. -56 dBm
D. -120 dBm
Answer: B
Clarification: Input noise power is given the expression kBTA. Here k is the Boltzmann’s constant, B is the operational bandwidth of the antenna and TA is the antenna noise temperature. Substituting in the above expression, input noise power is -115 dBm.

7. Antenna noise temperature of a system is 210 K, noise temperature of transmission line is 123 K, loss of a transmission line connecting the antenna to receiver is 1.41 and noise temperature of the receiver cascade is 304 K. then the total system noise temperature is:
A. 840 K
B. 762 K
C. 678 K
D. 1236 K
Answer: B
Clarification: The total system noise temperature is given by the expression TA+TTL+LTTREC. TA is the antenna noise temperature, TTL is the transmission line noise temperature, TREC is the noise temperature of receiver cascade. Substituting the given values, total system noise temperature is 762 K.

8. If the received power at antenna terminals is -80dBm, and if the input noise power is -115 dBm, then the input SNR is:
A. 45 dB
B. -195 dB
C. -35 dB
D. 35 dB
Answer: D
Clarification: Input SNR of a system is (Si-Ni) in dB. Substituting the given signal power and noise power in dB, input SNR of the system is 35 dB.

9. A receiver system is operating at a bandwidth of 1 MHz and has a total system noise temperature of 762 K. then the output noise power is:
A. -110 dBm
B. -234 dBm
C. -145 dBm
D. -124 dBm
Answer: A
Clarification: Output noise power of a receiver system is kBTsys. B is the operating bandwidth and Tsys is the total system noise temperature. Substituting the given values in the given equation, output noise power is -110 dBm.

10. If the received power at the antenna terminals is Si=-80 dBm and the output noise power is -110 dBm then the output signal to noise ratio is given by:
A. 30 dB
B. -30 dB
C. 35 dB
D. -35 dB
Answer: A
Clarification: Output signal to noise ratio in dB is given by (So-No). Substituting the given values in the above equation, the output SNR is 30 dB.


Microwave Engineering,

250+ TOP MCQs on Lumped Element Circuit Model of Transmission Line and Answers

Basic Microwave Engineering Questions on “Lumped Element Circuit Model of Transmission Line”.

1. The key difference between circuit theory and transmission line theory is:
A. circuit elements
B. voltage
C. current
D. electrical size
Answer: D
Clarification: Circuit theory assumes physical dimensions of the network smaller than electrical wavelength, while transmission lines may be considerable fraction of wavelength.

2. Transmission line is a _________ parameter network.
A. lumped
B. distributed
C. active
D. none of the mentioned
Answer: B
Clarification: Since no lumped elements like resistors, capacitors are used at microwave frequencies, only transmission lines are used. Hence they are called distributed parameter network.

3. For transverse electromagnetic wave propagation, we need a minimum of:
A. 1 conductor
B. 2 conductors
C. 3 conductors
D. bunch of conductors
Answer: B
Clarification: With a single conductor, transverse electromagnetic wave propagation is not possible. Hence we need a minimum of 2 conductors.

4. To model a transmission line of infinitesimal length Δz, the lumped element that is not used is:
A. resistor
B. inductor
C. capacitor
D. transistor
Answer: D
Clarification: In the lumped element circuit model of a transmission line, we use only resistor, capacitor and inductor. Hence no transistor is used.

5. _________ and __________ contribute to the impedance of a transmission line in the lumped element representation.
A. resistor, inductor
B. resistor, capacitor
C. capacitor, inductor
D. transistor, capacitor
Answer: A
Clarification: Z=R+jωL. Hence, both resistor and inductor contribute to the impedance of the transmission line.

6. _________ and __________ contribute to the admittance of a transmission line in the lumped element representation.
A. conductance G, capacitor
B. conductance, inductor
C. resistor, capacitor
D. resistor, inductor
Answer: A
Clarification:Y=G+jωC. Hence, both conductance and capacitance contribute to the admittance of the transmission line.

7. Characteristic impedance of a transmission line is:
A. impedance Z of a transmission line
B. impedance which is a constant at any point on the transmission line
C. reciprocal of admittance of a transmission line
D. none of the mentioned
Answer: B
Clarification: Characteristic impedance is defined as that impedance of a line which is a constant when measured at any point on the line, Hence B.

8. Propagation constant γ is a :
A. real value
B. none of the mentioned
C. imaginary value
D. complex value
Answer: C
Clarification: Since propagation constant is a complex value, containing attenuation constant α, phase constant β respectively as their real and imaginary parts.

9. Attenuation constant α signifies:
A. real part of propagation constant
B. loss that the transmission line causes
C. none of the mentioned
D. all of the mentioned
Answer: D
Clarification: α is the real value of propagation constant, also signifies the loss that the transmission line causes and hence the total amount of energy transmitted. Hence all the mentioned.

10. Propagation constant γ is given by:
A. α+jβ
B. α-jβ
C. α/jβ
D. α.jβ
Answer: A
Clarification: Propagation constant is a complex sum of α and β, α being the real value and β being the complex part.

11. Characteristic impedance Zₒ is given by:
A. √Z/Y
B. √ZY
C. √Z+√Y
D. √Z-√Y
Answer: A
Clarification: Characteristic impedance Zₒ is the square root of ratio of impedance and admittance of the transmission line.

12. Propagation constant γ in terms of admittance and impedance of the transmission line is:
A. √Z/Y
B. √ZY
C. ZY
D. ZY*
Answer: B
Clarification: Propagation constant is the root of product of impedance and admittance of the transmission line.


250+ TOP MCQs on Striplines and Answers

Microwave Engineering Multiple Choice Questions on “Striplines”.

1. Which mode of propagation is supported by a strip line?
A. TEM mode
B. TM mode
C. TE mode
D. None of the mentioned
Answer: A
Clarification: Since a stripline has 2 conductors and a homogeneous dielectric, it supports a TEM wave, and this is the usual mode of operation.

2. The higher order wave guide modes of propagation can be avoided in a strip line by:
A. Restricting both the ground plate spacing and the sidewall width to less than λd/2
B. Restricting both the ground facing plate spacing and the sidewall width to less than λd
C. Filling the region between 2 plates with di electric
D. Restricting both the ground plate spacing and the sidewall width between λg and λg/2
Answer: A
Clarification: When stripline is used as a media for propagation, it is always preferred that only certain modes of propagation are allowed. Hence, in order to avoid the higher order modes, it is achieved by restricting both the ground plate spacing and the sidewall width to less than λd/2.

3. Stripline can be compared to a:
A. Flattened rectangular waveguide
B. Flattened circular waveguide
C. Flattened co axial cable
D. None of the mentioned
Answer: C
Clarification: A stripline has an enter conductor enclosed by an outer conductor and are uniformly filled with a dielectric medium, these are similar to a coaxial cable. Hence it can be compared to a flattened coaxial cable.

4. If the dielectric material filled between the round plates of a microstrip line has a relative permittivity of 2.4, then the phase velocity is:
A. 1.3*108 m/s
B. 1.9*108 m/s
C. 3*108 m/s
D. 2*108 m/s
Answer: B
Clarification: Phase velocity is given by the expression C/√∈ for a stripline. Substituting the given values, the phase velocity for the above case is 1.9*108 m/s.

5. Expression for propagation constant β of a strip line is:
A. ω(√µ∈∈r)
B. ω(√µₒ/√∈r)
C. ω/(√µₒ∈ₒ∈r)
D.c/(√µₒ∈ₒ∈r)
Answer: A
Clarification: Propagation constant is associated with the propagating wave in the strip line. This propagation constant for a wave is defined by the expression ω(√µ∈∈r).

6. If the phase velocity in a stripline is 2.4*108m/s, and the capacitance per unit length of a micro stripline is 10pF/m, then the characteristic impedance of the line:
A. 50 Ω
B. 41.6 Ω
C. 100 Ω
D. None of the mentioned
Answer: B
Clarification: Characteristic impedance of a stripline is given by 1/ (vPC.. Substituting the given values of phase velocity and capacitance, the characteristic impedance of the line is 41.6 Ω.

7. The expression for characteristic impedance Zₒ of a stripline is:
A. (30πb/√∈r)(1/We+0.441B.
B. (30πB. (1/We+0.441B.
C. 30π/√∈r
D. (1/We+0.441B.
Answer: A
Clarification: Characteristic impedance of a stripline is a function of the various parameters of the stripline. They are effective width, thickness and relative permittivity of the dielectric material. Changing any one of these parameters results in changing the characteristic impedance of the line The derived expression is hence (30πb/√∈r)(1/We+0.441B..

8. If the effective width of the center conductor is 3 mm and the distance between the two ground plates is 0.32 cm with the material of the dielectric used having a relative permittivity of 2.5, then what is the characteristic impedance of the strip line?
A. 50Ω
B. 71.071Ω
C. 43.24Ω
D. 121Ω
Answer: C
Clarification: The characteristic impedance of a stripline is given by the expression (30πb/√∈r)(1/We+0.441B.. Substituting the given values in the given expression and hence solving, the characteristic impedance of the line is 43.24 Ω.

9. The wave number of a stripline operating at a frequency of 10 GHz is:
A. 401
B. 155
C. 206
D. 310
Answer: D
Clarification: The wave number of a microstrip line is given by the expression 2πf√∈r/c, c is the speed of light in space, ∈r is the relative permittivity of the dielectric medium. Substituting the given values in the equation, the wave number is 310.

10. If the loss tangent is 0.001 for a stripline operating at 12 GHz with the relative permittivity of the dielectric material being used equal to 2.6, then the conductor loss is:
A. 0.102
B. 0.202
C. 0.001
D. 0.002
Answer: B
Clarification: Conductor loss in a stripline is given by the expression k*tanδ/2. K is given by the expression 2πf√∈r/C which is the wave number. Substituting the values in the above two equations, conductor loss is 0.202.

11. If the dielectric material used between the grounded plates of a stripline is 2.2, when the strip line operating at 8 GHz, the wavelength on stripline is:
A. 1.2 cm
B. 2.52 cm
C. 0.15 cm
D. 3.2 cm
Answer: B
Clarification: The propagating wavelength on the stripline is defined by the relation C/f√∈r. substituting in the above relation, the propagating wavelength on the microstrip line is 2.52 cm.

12. Fields of TEM mode on strip line must satisfy:
A. Laplace’s equation
B. Ampere’s circuital law
C. Gaussian law
D. None of the mentioned
Answer: A
Clarification: If φ(x,y) is the function of potential in the stripline varying along the width and thickness, this potential function must satisfy the Laplace’s equation.


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250+ TOP MCQs on Rectangular Waveguide Cavity Resonators and Answers

Microwave Engineering Questions and Answers for Aptitude test on “Rectangular Waveguide Cavity Resonators”.

1. Microwave resonators can be constructed from open sections of waveguide.
A. True
B. False
Answer: B
Clarification: For resonance to occur in waveguides, a closed structure is required. They resonate between the walls of the rectangular waveguide. Also radiation loss from an open ended waveguide can be significant.

2. There is no energy stored inside a rectangular waveguide cavity resonator.
A. True
B. False
Answer: B
Clarification: Energy is stored in a waveguide resonator in the form of electric field and magnetic field. Power is dissipated in the metallic walls of the cavity as well as in the dielectric material that may fill the cavity.

3. A rectangular cavity supports:
A. TEM mode of resonance
B. TM mode of resonance
C. TE mode of resonance
D. TE, TM modes of resonance
Answer: D
Clarification: A rectangular wave guide supports both TE and TEM mode of propagation. Likewise, when a rectangular waveguide is used as resonator, it supports both TE and TM modes of resonance.

4. A waveguide is open circuited at both the ends to use it as a waveguide resonator.
A. True
B. False
Answer: B
Clarification: A closed cavity structure is required in order to bring resonance in the rectangular cavity. Also open ended waveguides result in radiation losses. Hence the waveguide is short circuited to form a resonator.

5. In order to obtain the resonant frequency of a rectangular waveguide, the closed cavity has to satisfy:
A. Gaussian equation
B. Helmholtz equation
C. Ampere’s law
D. None of the mentioned
Answer: B
Clarification: Helmholtz wave equation is considered and solved using variable separable form. Then the boundary conditions are applied to the wave equation considering the walls of the cavity. Solving this gives the expression for resonant frequency.

6. Given the dimension of the waveguide as bA. True
B. False
Answer: B
Clarification: For the given dimensional specification b

7. Unloaded Q of a rectangular waveguide cavity resonator:
A. Does not exist
B. Defined as the ratio of length of the waveguide to breadth of the waveguide
C. Defined as the ratio of stored energy to the power dissipated in the walls
D. None of the mentioned
Answer: C
Clarification: Quality factor signifies the power loss in the circuit. It is defined as the ratio of stored energy to the power dissipated in the walls. Higher the power dissipation in the walls, lower is the quality factor of the waveguide resonator.

8. Find the wave number of a rectangular cavity resonator filled with a dielectric of 2.25 and designed to operate at a frequency of 5 GHz.
A. 157.08
B. 145.2
C. 345.1
D. 415.08
Answer: A
Clarification: The wave number of rectangular wave resonator is 2πf√∈r/C, substituting the given values in the above equation, the wave number of the rectangular cavity resonator is 157.08.

9. The required length of the cavity resonator for l=1 mode (m=1, n=0) given that the wave number of the cavity resonator is 157.01 and the broader dimension of the waveguide is 4.755 cm:
A. 1.10 cm
B. 2.20 cm
C. 2.8 cm
D. 1.8 cm
Answer: B
Clarification: The required length of the cavity resonator for the given mode is given by the expression d=lπ/√(k>sup>2-(π/A.2. Substituting the given values in the equation, the required length of the waveguide is 2.20 cm.

10. If the loss tangent of a rectangular waveguide is 0.0004, then Q due to dielectric loss is:
A. 1250
B. 2450
C. 2500
D. 1800
Answer: C
Clarification: Q of a rectangular waveguide due to dielectric loss is given by 1/tanδ. Substituting for tanδ in the above equation, Q due to dielectric loss is 2500.


for Aptitude test,

250+ TOP MCQs on Noise in Micro – Wave Circuits and Answers

Microwave Engineering Multiple Choice Questions on “Noise in Micro – Wave Circuits”.

1. The type of noise caused by vibration of bound charges is called:
A. Thermal noise
B. Shot noise
C. Flicker noise
D. None of the mentioned
Answer: A
Clarification: Thermal noise is the most basic type of noise, being caused by thermal vibrations of bound charges in a material. When an electron bound to atom gains energy and vibrates, thermal noise is produced. It is also called as Johnson noise.

2. ________ noise occurs due to the random fluctuation of charge in an electron tube.
A. Flicker noise
B. Shot noise
C. Thermal noise
D. White noise
Answer: B
Clarification: Shot noise or Poisson noise is a type of electronic noise that can be modeled by Poisson process. This type of noise occurs due to the discrete nature of electric charge.

3. Flicker noise occurs in solid-state components and vacuum tubes.
A. True
B. False
Answer: A
Clarification: Flicker noise is a form of noise that exhibits an inverse frequency power density curve. It has a pink noise power density spectrum. Since this noise is inversely proportional to the operating frequency, it is called 1/f noise.

4.________ noise is caused by random motion of charges in ionized gas.
A. Plasma noise
B. Quantum noise
C. Thermal noise
D. Flicker noise
Answer: A
Clarification: Plasma noise is caused by random motion of charges in an ionized gas such as a plasma, ionosphere or sparking electrical contacts. A material medium is required to produce this type of noise.

5. The most insignificant form of noise is:
A. Plasma noise
B. Quantum noise
C. Shot noise
D. Flicker noise
Answer: B
Clarification: Quantum originates due to the quantized nature of charge carriers and photons. This noise does not pose any problem in microwave circuits and also does not affect the signal strength. Hence they are often significant.

6. An X- band amplifier has a gain of 20 dB and a gain of 1GHz bandwidth. Noise figure of the amplifier is -62 dBm at 290 K and -64.7 dBm at 77 K. then the Y factor of the amplifier is :
A. 3 dB
B. 6.4 dB
C. 2.7 dB
D. 5.6 dB
Answer: C
Clarification: The Y factor of an amplifier is given by the difference in noise figure of the amplifier measured at two different temperatures. Taking the difference of the two values, the Y factor is 2.7 dB.

7. The Y factor of an amplifier obtained by measuring the noise figure at the temperatures 77 K and 290 K is 2.7 db. Then the equivalent noise temperature of the amplifier is:
A. 100 K
B. 150 K
C. 170 K
D. None of the mentioned
Answer: C
Clarification: The equivalent noise temperature of the amplifier is given by the relation (T1-YT2)/(Y-1). Substituting the given values in the above equation, equivalent noise temperature is 170 K.

8. An amplifier has a noise equivalent temperature of 170 K. If the amplifier is used with a source having an equivalent noise temperature of TS=450 K, the output noise power of the amplifier is:
A. -50 dBm
B. -60 dBm
C. -60.7 dBm
D. -55 dBm
Answer: C
Clarification: Output noise power of an amplifier is given by the expression GkTSB + GkTeB Substituting the given values in the above expression, the output noise power of the amplifier is -60.7 dBm.

9. The noise power associated with a two port network modeled as thevinin equivalent is:
A. kTB
B. k/TB
C. TB/ K
D. None of the mentioned
Answer: A
Clarification: Noise associated with a 2 port network modeled as thevinin equivalent is kTB. K is the Boltzmann constant, T is the temperature and B is the operating bandwidth of the circuit.

10. Excess noise ratio is defined as the ratio of generator noise to the noise associated with room temperature
A. True
B. False
Answer: B
Clarification: Excess noise ratio is defined as the ratio of the difference in noise power of the generator and noise power associated with the room temperature to the noise power associated with room temperature.

11. Equivalent noise temperature associated with an arbitrary white noise source is:
A. N0/GKB
B. N0
C. N0/ kB
D. None of the mentioned
Answer: A
Clarification: Equivalent noise temperature associated with an arbitrary white noise source is N0/GKB. Here N0 is the noise power delivered to the load resistor by the source, B is the operating bandwidth G is the gain of the circuit.


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