Category: Microwave Engineering Objective Questions

250+ TOP MCQs on Noise Figure and Answers

Microwave Engineering Multiple Choice Questions on “Noise Figure”.

1. ___________ 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
Clarification: SNR is defined as the ratio of desired signal power to undesired noise power, and so is dependent on the signal power. When noise and a desired signal are applied to the input of a noise less network, both noise and signal will be attenuated or amplified by the same factor, so that the signal to noise ratio will be unchanged.

2. __________ 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
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.

3. 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
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.

4. Noise figure can be defined for any microwave network irrespective of any other constraints.
A. True
B. False

Answer: B
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.

5. 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
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.

6. Noise equivalent temperature of a transmission line that adds noise to the noise of a device is:
A. T (L-1)
B. T (L+1)
C. T (L)
D. T/L

Answer: A
Clarification: Noise equivalent temperature of a transmission line that adds noise to the noise of a device is given by T (L-1). Here L is the loss factor of the line and T is the temperature at which the system is thermal equilibrium.

7. If the noise figures of the first stage of a two stage cascade network is 8 dB and the noise figure of the second stage is 7 dB and the gain of the first stage is 10, then the noise figure of the cascade is:
A. 8. 6 dB
B. 7.6 dB
C. 5.6 dB
D. 8.9 dB

Answer: A
Clarification: Noise figure of a two stage cascade network is given by F1+ (F2-1)/G1. Here F1, F2 are the noise figure of the first and the second stage respectively. G1 is the gain of the first stage. Substituting the given values in the above equation, noise figure of the cascade is 8.6 dB.

8. 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
Clarification: Noise equivalent temperature of a 2 stage cascade network is given by Te1 + Te1/ G1. Here, Te1 is the noise equivalent temperature of stage 1 and Te1 is the noise equivalent temperature of stage 2. G1 is the gain of the first stage of the amplifier.

9. When a network is matched to its external circuitry, the gain of the two port network is given by:
A. │S21│2
B. │S22│2
C. │S12│2
D. │S11│2

Answer: A
Clarification: The gain of a two port network is given by the product of SS21 of the network and reflection co-efficient at the source end. But when the two port network is matched to the external circuitry, reflection coefficient becomes zero and gain reduces to │S21│2.

10. 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
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.

11. 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
Clarification: Noise equivalent temperature of the Wilkinson coupler is found using the relation
T (1-G21)/G21. Substituting for G21 in the above expression, equivalent noise temperature is T (2L-1).

12. 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
Clarification: The overall noise figure of a mismatched amplifier is given by 1+ (F-1)/ (1 -│Г│2). Here F is the noise figure of the amplifier, when there is an impedance mismatch at the input of the amplifier; this impedance mismatch is given by Г.

250+ TOP MCQs on Single Stage Transistor Amplifier Design and Answers

Microwave Engineering online test on “Single Stage Transistor Amplifier Design”.

1. The overall gain of a transistor is always a fixed value and cannot be changed as per design requirements.
A. True
B. False
Answer: B
Clarification: For a given transistor gain G0 is a fixed value and cannot be changed. But the overall transducer gain of the amplifier will be controlled by GS and GL, of the matching section used with the transistor.

2. The frequency response of an amplifier is _______
A. Wide band
B. Narrow band
C. Pass band
D. None of the mentioned
Answer: B
Clarification: Most transistors exhibit a significant impedance mismatch (large S11 and S22). This results in a frequency response of the transistor that being narrow band.

3. Maximum power transfer from the input matching port to the transistor will occur when:
A. Гin=Г*S
B. Гin=ГS
C. Гin=ГS. ejω
D. None of the mentioned
Answer: A
Clarification: For a transistor, ГS is the reflection co-efficient of the amplifier looking towards the source. Гin is the reflection coefficient of the amplifier looking towards the input terminals of an amplifier. For maximum power transfer, the above mentioned condition must be satisfied.

4. The condition for maximum power transfer from the transistor to the output matching network will occur when:
A. Гout=ГL*
B. Гout=ГL
C. Гout=1/ ГL
D. Гout=1/ ГL*2
Answer: A
Clarification: The condition for maximum power transfer from the transistor to the output matching network will occur when Гout=ГL*. ГL is the reflection coefficient seen looking towards the load. Гout is the looking towards the output ports of the transistor.

5. The input and output ports of an amplifier are always matched to the impedance Z0 .
A. True
B. False
Answer: A
Clarification: With two different matching techniques called conjugate matching and lossless matching sections, the input and output ports of a transistor are matched to the characteristic impedance Z0 of the feed line used.

6. Unconditionally stable devices can always be ____________ for maximum gain.
A. Lossless matched
B. Conjugate matched
C. Forward biased
D. Driven with high current
Answer: B
Clarification: Unconditionally stable devices can always be conjugate matched for maximum power gain and potentially unstable devices can be conjugate matched if K>1 and │∆│<1.

7. The maximum transducer gain occurs when the source and the load are matched to the impedance Z of the transistor by lossless method.
A. True
B. False
Answer: B
Clarification: The maximum transducer power gain occurs when the source and load are conjugated matched to the transistor. This matched condition can be verified using the relation between the reflection coefficients.

8. Maximum transducer gain for an amplifier is the same as the maximum gain for an amplifier.
A. True
B. False
Answer: A
Clarification: Maximum transducer gain is also referred to as matched gain. Maximum gain does not give a meaningful result when the device is only conditionally stable, since the simultaneous conjugate match of the load and source is not possible simultaneously.

9. In terms of S parameters for a transistor, the transducer gain is given by the relation:
A. │S21│/│S12│
B. │S12│/│S21│
C. │S22│/│S11│
D. │S11│/│S22│
Answer: A
Clarification: Transducer power gain is defined as the ratio of power measured at the port 2 (output port) to the ratio of the power at the input port. This is redefined in terms of the S parameter of the network and can be written as │S21│/│S12│.

10. In the S matrix of a transistor, if the parameter S21 is 2.6 then the gain G0 of the transistor has the value
A. 6.2 dB
B. 8.3 dB
C. 2.22 dB
D. None of the mentioned
Answer: B
Clarification: Gain G0 of a transistor amplifier is given as 10 log S12. Substituting for S12 in the equation, then the gain G0 of the amplifier is given by 8.3 dB.


250+ TOP MCQs on Radiometer Systems and Answers

Microwave Engineering Multiple Choice Questions on “Radiometer Systems”.

1. __________ system obtains information about a target by transmitting a signal and receiving the echo from the target.
A. Radar
B. Sonar
C. Radiometer
D. None of the mentioned
Answer: A
Clarification: Radar stands for radio detection and ranging. A radar system obtains information about a target by transmitting a signal and receiving the echo from the target. They are also called as active remote sensing systems.

2. Radiometry is a technique or the principle on which radar works.
A. True
B. False
Answer: B
Clarification: Radiometry is a passive technique which develops information about a target solely from the microwave portion of the blackbody radiation that it either emits directly or reflects from the surrounding bodies.

3. According to Planck’s radiation law, a body can radiate energy to the medium surrounding it under all conditions invariably.
A. True
B. False
Answer: B
Clarification: A body in thermal equilibrium only can radiate energy according to Planck’s radiation law. The radiating body has to be maintained in thermal equilibrium. In the microwave region this reduces to P=kTB, where k is the Boltzmann’s constant.

4. A major challenge in designing a radiometer is:
A. Design complexity
B. High cost
C. Requirement of highly sensitive receivers
D. None of the mentioned
Answer: C
Clarification: The basic problem with building a radiometer is to build a receiver that can distinguish between the desired external radiometric noise and the inherent noise of the receiver. This application thus requires that are highly efficient in detecting the required signal.

5. The receiver model of a total power radiometer is based on the:
A. AM receiver
B. FM receiver
C. Super heterodyne receiver
D. None of the mentioned
Answer: C
Clarification: The front end of a receiver is a standard super heterodyne circuit consisting of an RF amplifier, a mixer/ local oscillator, and an IF stage. These stages are the same as that used in a super heterodyne receiver.

6. The system bandwidth of a total power radiometer is determined by the:
A. RF amplifier
B. Local oscillator
C. IF filter
D. IF amplifier
Answer: C
Clarification: The system bandwidth of a total power radiometer is determined by the IF filter section present in the receiver circuit of the radiometer. The upper and lower cutoff frequency of the IF filter specify the system bandwidth.

7. The integrator circuit after the detector in the receiver circuit is used to smooth out the short term variations in the signal power.
A. True
B. False
Answer: B
Clarification: The integrator used is essentially a low pass filter with a fixed cutoff frequency, and serves to smooth out short term variations in the noise power.

8. The dominant factor affecting the accuracy of the total power radiometer is the variation of ___________
A. Gain in the overall system
B. The feedback circuit
C. Efficiency of the system
D. None of the mentioned
Answer: A
Clarification: The dominant factor affecting the accuracy of the total power radiometer is the variation of the gain of the overall system. Since such variations have relatively a longer time constant, it is possible to eliminate this error by repeatedly calibrating the device.

9. A Dicke radiometer is identical to the total power radiometer in all aspects except that they have different receiving antenna.
A. True
B. False
Answer: B
Clarification: In a Dicke radiometer, the input is periodically switched between the antenna and a variable power noise source. This switch is called Dicke switch. Repeatedly calibrating the device is the principle behind the operation of Dicke radiometer.

10. A typical radiometer would measure the brightness temperature over the range of about:
A. 50-300 K
B. 100-200 K
C. 400-500 K
D. None of the mentioned
Answer: A
Clarification: Typical radiometer would measure the brightness temperature over the range of about 50-300K. This then implies that the reference noise source would have to cover the same range, which is difficult to achieve practically.


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250+ TOP MCQs on Field Analysis of Transmission Lines and Answers

Microwave Engineering Multiple Choice Questions on “Field Analysis of Transmission Lines”.

1. In a two wire transmission line, if the distance between the lines is 20 mm and the radii is 5 mm then the inductance of the line is:
A. 0.1 µH
B. 0.526 µH
C. 0.9 µH
D. 1 µH
Answer: B
Clarification: The inductance of a two wire transmission line is given by the equation µ*ln(b/A./2π. Substituting the given values in the above equation, inductance is 0.526 µH.

2. In a two wire transmission line , if the distance between the lines is 60mm and the radii is 10 mm , then the capacitive reactance of the line when operated at 12.5 GHz is
A. 20 pF
B. 21.13 pF
C. 23 pF
D. 12 pF
Answer: B
Clarification: The capacitive reactance of a two wire transmission line is π∈/cosh-1(D/2A.. substituting the given values in the above expression, the capacitive reactance is 21.13 pF.

3. For a parallel plate type of a transmission line, then expression for conductance of the line is:
A. ∈(ω)w/d
B. 2Rx/x
C. μ/2π ln⁡(w/D.
D. μ/π cosh-1(w/2D.
Answer: A
Clarification: The conductance of a parallel plate waveguide is dependent on the complex value of the permittivity, width of the waveguide and the distance between the waveguide plates.

4. One of the Maxwell‘s curl equation that is satisfied inside a coaxial line is:
A. ∇×E =-jωµ (vector H)
B. ∇×E =-jωμ(vector E)
C. ∇×H=-jωμ(vector H)
D. ∇×H=jωμ(vector H)
Answer: A
Clarification: ∇×E = -jωµ (vector H).This is the Maxwell’s equation satisfied by the electric and magnetic fields inside a waveguide.

5. The wave impedance of air for a wave propagating in it is:
A. 377 Ω
B. 345 Ω
C. Insufficient data
D. None of the mentioned
Answer: A
Clarification: Intrinsic impedance is the impedance offered by air for a wave propagating in it. This is a standard value and is 377 Ω.

6. Wave impedance of a wave travelling in a medium of a relative permittivity 2 and permeability 4 is
A. 188.5 Ω
B. 200 Ω
C. 300 Ω
D. None of the mentioned
Answer: A
Clarification: Intrinsic impedance of a medium is given by the expression √μ/ϵ. Substituting the given values in the above expression, the wave impedance is 188.5 Ω.

7. For a parallel plate transmission line, if w= 12 mm and the distance between the plates is 2 mm, then the inductance of the transmission line is:
A. 0.2 µH
B. 0.1 µH
C. 0.3 µH
D. 0.4 µH
Answer: A
Clarification: The inductance of a parallel plate transmission line is given by µd/W. substituting the given values in the above expression, the inductance is 0.2 µH.

8. Expression for capacitance of a two wire transmission line is
A. ∈’*π/cosh⁡-1(D/2A.
B. μ/π*cosh-1(D/2A.
C. 2π∈/ln⁡(D/2A.
D. ∈”*πω/cosh-1(D/2A.
Answer: A
Clarification: The expression for capacitance of a two wire transmission line is ∈’ π/cosh-1(D/2A.. Capacitance of a two wire transmission line is dependent on the distance between the two lines and the radius of the line.

9. If the distance between the 2 wires in a 2 wire transmission line is 10 mm and the radii 2 mm, then the inductance of the transmission line is:
A. 0.62 µH
B. 1 µH
C. 2 µH
D. None of the mentioned
Answer: A
Clarification: The inductance of a two wire transmission line is given by the expression µcosh-1(D/2A./π. Substituting the given values in the above expression, the inductance is 0.62 µH.

10. For a parallel plate transmission line, if the complex part of permittivity is 2.5, if the width is 100 mm and the distance between the plates is 10 mm, then the conductance of the transmission line is:
A. 25 Ʊ
B. 30 Ʊ
C. 45 Ʊ
D. None of the mentioned
Answer: A
Clarification: Conductance of a parallel plate transmission line is ∈W/d. substituting the given values in the above expression, the conductance of the transmission line is 25 Ʊ.

11. For a parallel plate transmission line, if the series resistance is 10 mΩ/m, and the width is 100 mm, then the resistance of the transmission line is:
A. 0.2 Ω
B. 1 Ω
C. 2 Ω
D. 5 Ω
Answer: A
Clarification: For a parallel plate transmission line, the series resistance is given by the expression 2RS/W. substituting the given values in the above expression, the series resistance is 0.2 Ω.


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250+ TOP MCQs on Impedance and Admittance Matrices and Answers

Microwave Engineering Assessment Questions on “Impedance and Admittance Matrices”.

1. The one below among others is not a type TEM line used in microwave networks:
A. Co-axial wire
B. Micro strip line
C. Strip lines
D. Surface guide
Answer: D
Clarification: Coaxial micro strip and strip lines all support TEM mode of propagation through them. But surface guides do not support TEM mode of propagation in them. Hence it cannot be called a TEM line.

2. The one below is the only micro wave network element that is a TEM line:
A. Co-axial cable
B. Rectangular wave guide
C. Circular wave guide
D. Surface wave guide
Answer: A
Clarification: Coaxial cables support TEM mode of propagation in them and rectangular waveguide, circular wave guide, surface waveguides do not support TEM mode of propagation in them.

3. The relation between voltage, current and impedance matrices of a microwave network is:
A. [V] = [Z][I].
B. [Z] = [V][I].
C. [I] = [Z][V].
D. [V] = [Z]-[I].
Answer: A
Clarification: In microwave networks, at any point in a network, the voltage at a point is the product of the impedance at that point and current measured. This can be represented in the form of a matrix.

4. The relation between voltage, current and admittance matrices of a microwave network is:
A. [I] = [Y] [V].
B. [Y] = [V] [I].
C. [I] = [Z] [V].
D. [V] = [Z]-1[I].
Answer: A
Clarification: The relation between voltage current and admittance matrices is [I] = [Y] [V]. here I represents the current matrix, Y is the admittance matrix and V is the voltage matrix.

5. Admittance and impedance matrices of a micro waves network are related as:
A. [Y] = [Z]-1.
B. [Y] = [Z].
C. [V] = [Z] [Z]-1.
D. [Z] = [V] [V]-1.
Answer: A
Clarification: Both admittance and impedance matrix can be defined for a microwave network. The relation between these admittance and impedance matrix is [Y] = [Z]-1. Admittance matrix is the inverse of the impedance matrix.

6. The element of a Z matrix, Zij can be given in terms of voltage and current of a microwave network as:
A. ZIJ = VI/IJ
B. ZIJ = VIIJ
C. 1//ZIJ = 1/JIVI
D. VIJ = IJ/JI
Answer: A
Clarification: The element Zij of a Z matrix is defined as the ratio of voltage at the ith port to the current at the jth port given that all other currents are set to zero.

7. In a two port network, if current at port 2 is 2A and voltage at port 1 is 4V, then the impedance Z₁₂ is:
A. 2 Ω
B. 8 Ω
C. 0.5 Ω
D. Insufficient data
Answer: A
Clarification: Z12 is defined as the ratio of the voltage at port 1 to the current at port 2. Substituting the given values in the above equation, Z12 parameter of the network is 2 Ω.

8. In a 2 port network, if current at port 2 is 2A and voltage at port 1 is 4 V, then the admittance Y₂₁ is:
A. 0.5 Ʊ
B. 8 Ʊ
C. 2 Ʊ
D. 4 Ʊ
Answer: A
Clarification: Admittance parameter Y12 is defined as the ratio of current at port 1 to the voltage at port 2. Taking the ratio, the admittance Y12 is 0.5 Ʊ.

9. For a reciprocal network, Z matrix is:
A. A unit matrix
B. Null matrix
C. Skew symmetric matrix
D. Symmetric matrix
Answer: D
Clarification: For a reciprocal matrix, the impedance measured at port Zij is equal to the impedance measured at port Zji. Since these parameters occupy symmetric positions in the Z matrix, the matrix becomes symmetric.

10. For a lossless network, the impedance and admittance matrices are:
A. Real
B. Purely imaginary
C. Complex
D. Rational
Answer: B
Clarification: For a network to be lossless, the network should be purely imaginary. Presence of any real component implies the presence of resistance in the network from which the network becomes lossy. So the matrices must be purely imaginary.

11. The matrix with impedance parameters Z₁₁=1+j, Z₁₂=4+j, Z₂₂=1, Z21=4+j is said to be
A. Reciprocal network
B. Lossless network
C. Lossy network
D. None of the mentioned
Answer: A
Clarification: In the given case, Z12=Z21. This condition can be satisfied only by reciprocal networks. Hence the given network is a reciprocal network.


Assessment Questions,

250+ TOP MCQs on Dielectric Resonators and Answers

Microwave Engineering Multiple Choice Questions on “Dielectric Resonators”.

1. A dielectric material in the form of a small cube or disc can be used as a resonator.
A. true
B. false
Answer: A
Clarification: A dielectric material in the form of a small cube or disc can be used as a resonator. It has the same operating principles as that of a rectangular waveguide resonator and a circular waveguide resonator.

2. Dielectric resonators use materials that are less lossy.
A. true
B. false
Answer: A
Clarification: Dielectric resonators use materials that are less lossy and have high dielectric constant, ensuring that most of the fields will be contained in the dielectric.

3. The major disadvantage of dielectric resonators is:
A. complex construction
B. field fringing
C. requirement of high dielectric constant
D. none of the mentioned
Answer: B
Clarification: The major disadvantage of dielectric resonators is field fringing or leakage from sides and ends of a dielectric resonator. This leakage of field energy results in high loss.

4. One of the most commonly used dielectric materials is:
A. barium tetratetanate
B. titanium
C. teflon
D. none of the mentioned
Answer: A
Clarification: Materials having dielectric constant in the range of 10-100 are used in dielectric resonators and one more required characteristic property is low loss. Barium tetratetanate has all these properties. Hence it is most commonly used.

5. The resonant frequency of a dielectric resonator cannot be mechanically tuned.
A. true
B. false
Answer: A
Clarification: By using an adjustable metal plate above the resonator, the resonant frequency can be mechanically tuned. As it has these desirable features, it is mostly used in integrated microwave filters and oscillators.

6. If a dielectric resonator has a dielectric constant of 49, then the reflection coefficient of the dielectric resonator is:
A. 0.5
B. 0.75
C. 0.1
D. 0.7
Answer: B
Clarification: Reflection co-efficient of a dielectric resonator is given by (√∈r-1)/ (√∈r-1). Given that dielectric constant is 49, the reflection coefficient is 0.75.

7. Q factor does not exist for dielectric resonator.
A. true
B. false
Answer: B
Clarification: Q factor exists for a dielectric resonator .it is defined as the ratio of the energy stored in the dielectric to the energy dissipated and other losses that may occur.

8. The approximate loaded Q due to dielectric loss for a dielectric resonator given the loss tangent is 0.0001 is:
A. 1000
B. 500
C. 2000
D. 10000
Answer: A
Clarification: Loaded Q due to dielectric loss for a dielectric resonator is given by the reciprocal of the loss tangent. Taking the reciprocal of loss tangent, loaded Q due to dielectric loss is 1000.

9. The direction of propagation is in z direction outside the dielectric in the resonator.
A. true
B. false
Answer: B
Clarification: In a dielectric resonator, the direction of propagation can occur along the Z direction in the dielectric at resonant frequency but the fields are cutoff in the air region around the dielectric.

10. A dielectric resonator is considered to be closed at both the ends.
A. true
B. false
Answer: B
Clarification: For all analysis purpose, a dielectric resonator is considered to be of a short length L and termed as dielectric waveguide open at both the ends.


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