Category: Microwave Engineering Objective Questions

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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250+ TOP MCQs on Non – Linear Distortion – 1 and Answers

Microwave Engineering Multiple Choice Questions on “Non – Linear Distortion – 1”.

1. Active devices like diodes and transistors become non-linear at high power levels due to:
A. Instability of transistor
B. Thermal noise
C. Gain compression
D. None of the mentioned
Answer: C
Clarification: All practical components become non-linear at high power level operations. Active devices like diode and transistor become non-linear at high power levels due to effects such as gain compression or the generation of spurious frequency components due to device non-linearities, but all devices ultimately fail at very high power levels.

2. The ________property of devices like diodes and transistors is responsible for their usage in amplifiers and frequency convertors.
A. Symmetry
B. Non linearity
C. Linearity
D. None of the mentioned
Answer: B
Clarification: Non linearity is of great utility for desirable functions such as amplification, detection and frequency and frequency conversion. But non-linearities in these devices lead to undesirable effects like gain compression and generation of spurious frequency components.

3. The output response of a non-linear circuit is given by the expression:
A. V0=a0+a1Vi1+a2Vi2+a3Vi3…
B. 0=a0+a1Vi1
C. V0=a2Vi2+a3Vi3
D. V0=a0
Answer: A
Clarification: The output of non-linear devices in terms of the applied output voltage is given as the Taylor series in terms of the input signal voltage. This expansion is given by V0=a0+a1Vi1+a2Vi2+a3Vi3….
And higher order terms. The constant term leads to rectification converting an AC input signal to DC.

4. As the degree of non-linearity of a transistor or a diode increases, the power gain of the device:
A. Increases
B. Decreases
C. Remains a constant
D. None of the mentioned
Answer: B
Clarification: Let V0cosωt be the input signal applies to a non linear device. The output of the device is given by V0=a0+a1Vi+a2Vi2+a3Vi3. Considering only up to power of 3 and expanding, we get terms, whose constants of third degree and higher order are negative. This results in fall in gain when the input signal levels are high.

5. The fall in gain of a device due to non-linearities is called:
A. Gain compression
B. Gain saturation
C. Impedance mismatch
D. None of the mentioned
Answer: A
Clarification: The fall in gain of a device due to non-linearities is called gain compression. Physically, this is usually due to fact that the instantaneous output voltage of an amplifier is limited by the power supply voltage used to bias the active device.

6. 1 dB compression point is defined as the power level for which the output power of the non-linear device is 1 dB
A. True
B. False
Answer: B
Clarification: 1 dB compression point is defined as the power level for which the output power is decreased by 1dB from the ideal linear characteristic. This power level is represented as P1dB and can be stated in terms of either input power or output power.

7. In a non-linear device, for a single input frequency the output will consist of:
A. Single frequency component
B. Harmonics of the input frequency
C. Constant gain
D. None of the mentioned
Answer: B
Clarification: Let V0cosωt be the input signal applies to a non linear device. The output of the device is given by V0=a0+a1Vi1+a2Vi2+a3Vi3. Substituting in this equation gives higher frequency components which is associated with higher order terms in the expansion. When the input consists of only one frequency component the higher frequencies are filtered out using band pass filter.

8. When the input frequency consists of more than one closely spaced frequency, it results in:
A. Intermodal distortion
B. Gain compression
C. Signal fading
D. Signal attenuation
Answer: A
Clarification: When the input frequency consists of more than one frequency, due to the non-linear effect of the device, higher frequency components are generated. When the two different frequencies are close enough to each other, due to the interference of multiple frequency components, intermodal distortion occurs.

9. Third-order intercept point is defined as the point at which the gain of a non linear device is 3 dB less than the maximum gain.
A. True
B. False
Answer: B
Clarification: Third-order intercept point is defined as hypothetical intersection point at which the first order and third order powers would be equal is called the third-order intercept point.

10. The relation between an intercept points referenced at the input versus the output is given by the relation:
A. OIP3=G (IIP3)
B. (IIP3) = G (OIP3)
C. OIP3=G (IIP3)2
D. None of the mentioned
Answer: A
Clarification: The relation between an intercept points referenced at the input versus the output is given by the relation OIP3=G (IIP3). Here OPI3 is the output third order intercept point; OIP3 is the input third order intercept point. G is the conversion loss in the device.


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250+ TOP MCQs on Broadband Transistor Amplifier Design and Answers

Microwave Engineering Multiple Choice Questions on “Broadband Transistor Amplifier Design”.

1. 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
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.

2. 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
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.

3. 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
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.

4. 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
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.

5. 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
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.

6. Distributed amplifiers offer very high _________
A. gain
B. bandwidth
C. attenuation
D. none of the mentioned
Answer: B
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.

7. In distributed amplifiers, all the FET stages in the amplifier are connected in series to one another.
A. true
B. false
Answer: B
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.

8. ____________ 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
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.

9. 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
Clarification: Differential amplifiers can provide higher voltage swings that are approximately double that obtained with single ended amplifier.

10. Along with a differential amplifier, 1800 hybrid is used both at the input and output.
A. true
B. false
Answer: A
Clarification: A differential amplifier can be constructed using two single-ended amplifiers and 1800 hybrids at the input and output to split and then recombine the signals.


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