ECE : Microwave Communication - Quiz(MCQ)
A)
increases
B)
decreases
C)
remain the same
D)
decreases or remains the scheme

Explanation : Charging current and MVAR are proportional to frequency.

A)
input cavity
B)
output cavity
C)
intermediate cavity
D)
Both (A) and (B)

Explanation : A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

A)
Cavity match
B)
Waveguide match
C)
Direct coax-helix match
D)
All of the above

Correct Answer :   All of the above

A)
Low-pass filters
B)
The shortest possible time
C)
A long time constant
D)
The restricted high-frequency response

Correct Answer :   The shortest possible time

A)
current
B)
voltage
C)
electrical size
D)
circuit elements

Explanation : Circuit theory assumes physical dimensions of the network smaller than electrical wavelength, while transmission lines may be considerable fraction of wavelength.

A)
active
B)
distributed
C)
lumped
D)
None of the above

Explanation : Since no lumped elements like resistors, capacitors are used at microwave frequencies, only transmission lines are used. Hence they are called distributed parameter network.

A)
1 conductor
B)
2 conductors
C)
3 conductors
D)
bunch of conductors

Explanation : With a single conductor, transverse electromagnetic wave propagation is not possible. Hence we need a minimum of 2 conductors.

A)
1Â°
B)
30Â°
C)
70Â°
D)
90Â°

Explanation : For ideal dielectric loss angle is zero. For good quality cables, loss angle is very small, about 1° only.

A)
isolation (dB) equals (coupling) (directivity)
B)
coupling (dB) equals isolation plus directivity
C)
directivity (dB) equals isolation plus coupling
D)
isolation (dB) equals coupling plus directivity

Correct Answer :   isolation (dB) equals coupling plus directivity

Explanation : Isolation equals coupling plus directivity.

A)
skin effect
B)
temperature
C)
relative permittivity of dielectric
D)
None of the above

Correct Answer :   relative permittivity of dielectric

Explanation :

r of a dielectric changes with humidity.

A)
buncher
B)
catcher
C)
collector
D)
Pierce gun

Explanation : A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

A)
TEâ‚€â‚
B)
TEâ‚â‚
C)
TEâ‚‚â‚€
D)
TEâ‚‚â‚

Explanation :

Some applications require dual polarization capability. Circular waveguide has this capability.

These analysis uses cylindrical coordinates.

In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode.

If D is diameter of waveguide

λc = 1.706 D for TE11 mode

λc = 1.029 D for TE21 mode

λc = 0.82 D for TE01 mode

λc = 1.306 D for TM01 mode.

A)
microwave oscillators
B)
microwave frequency metres
C)
microwave narrow band amplifier
D)
All of the above

Correct Answer :   All of the above

A)
increases linearly
B)
is almost constant
C)
increases exponentially
D)
decreases exponentially

Explanation : In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

The velocity of wave propagation along the helix structure is less than velocity of light.

The beam and wave travel along the structure at the same speed.

Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

The main features of TWT are :

1. Frequency range - 0.5 GHz to 90 GHz

2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

A)
To focus the beam of primary electrons
B)
To shield the electron beam from unidirectional magnetic
C)
As a second anode and to prevent the build-up of secondary field
D)
All of the above

Correct Answer :   As a second anode and to prevent the build-up of secondary field

A)
Capacitor
B)
RF emitter
C)
Varactor-triac
D)
Ferrite emitter

A)
By bunches of electrons passing the cavity grids
B)
By plate-to-cathode feedback
C)
By circulating bunches of electrons within the cavities.
D)
By feedback between the accelerating grid and the repeller

Correct Answer :   By bunches of electrons passing the cavity grids

A)
B)
Indicates both the range and azimuth of a target
C)
Indicates only the range of a target
D)
Is used to check the percentage of modulation

Correct Answer :   Indicates both the range and azimuth of a target

A)
Lowering the pulse frequency
B)
Raising the peak power of the transmitter
C)
Narrowing the beam width and increasing the pulse duration
D)
All of the above

Correct Answer :   All of the above

A)
Gunn diode
B)
Reflex klystron
C)
Magnetron
D)
Traveling-wave tube

A)
transistor
B)
resistor
C)
inductor
D)
capacitor

Explanation : In the lumped element circuit model of a transmission line, we use only resistor, capacitor and inductor. Hence no transistor is used.

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 above

Correct Answer :   impedance which is a constant at any point on the transmission line

Explanation : Characteristic impedance is defined as that impedance of a line which is a constant when measured at any point on the line

A)
real value
B)
complex valuev
C)
imaginary value
D)
None of the above

Explanation : Since propagation constant is a complex value, containing attenuation constant α, phase constant β respectively as their real and imaginary parts.

A)
real part of propagation constant
B)
loss that the transmission line causes
C)
Both (A) and (B)
D)
None of the above

Correct Answer :   Both (A) and (B)

Explanation : 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.

A)
0
B)
1
C)
Infinity
D)
Data insufficient

Explanation : α-for a transmission line signifies the attenuation constant. For a lossless transmission line attenuation constant is zero and the propagation occurs without losses.

A)
Î±=12, Î²=20.6
B)
Î±=6, Î²=10.39
C)
Î±=61, Î²=78
D)
None of the above

Explanation : The given propagation constant is in polar form .converting from polar form to rectangular form and equating the real and imaginary parts, we get α=6 and β=10.39.

A)
132
B)
50
C)
20
D)
0

Explanation : β=ω√LC. Since both the line impedance and line admittance are both real, there is no phase difference caused and hence substituting in the above equation, we get β=0.

28 .
A microwave generator at 1.2 GHz supplies power to a microwave transmission line having the parameters R=0.8Ω/m, G=O.8millisiemen/m, L=0.01µH/m and C=0.4PF/m. Propagation constant of the transmission line is:
A)
0.0654 +j0.48
B)
0.064+j4.8
C)
6.4+j4.8
D)
None of the above

Explaination : Z=R+jωL and Y=G+jωC, hence finding out Z and Y from these equations, substituting in γ=√ZY, value of γ is found out to be 0.0654+j0.48.

29 .
In a certain microwave transmission line, the characteristic impedance was found to be 210 10°Ω and propagation constant 0.2 78°.What is the impedance Z of the line, if the frequency of operation is 1 GHz?
A)
35.6+j4.28
B)
9.254+j4.6
C)
0.35+j4.97
D)
0.035+j41.97

Explaination : Impedance Z of a transmission line is given by the product of propagation constant γ and characteristic Zâ‚’, Z= γZâ‚’ , we get Z=0.035+j41.97.

A)
TM, TE modes
B)
TEM, TE modes
C)
TEM, TE, TM modes
D)
TEM, TM modes

Correct Answer :   TEM, TE, TM modes

Explanation : Parallel plate waveguide is the simplest type of waveguide that can support TE and TM modes. It can also support a TEM mode since it is formed from two flat conducting plates.

A)
The dielectric material used
B)
Material of the parallel plate waveguide used
C)
Width of the plates is greater than the distance between the plates
D)
None of the above

Correct Answer :   Width of the plates is greater than the distance between the plates

Explanation : The strip width W of the parallel plate waveguide is assumed to be much greater than the separation d, hence the fringe effect or the fringing fields can be neglected.

32 .
If the width of a parallel plate waveguide is 30 mm and the distance between the parallel pates is 5 mm, with an intrinsic impedance of 377Ω, then the characteristic impedance of the wave is:
A)
50 Ω
B)
62.833 Ω
C)
100 Ω
D)
None of the above

Explaination : The expression for intrinsic impedance of a parallel plate waveguide is η*D/W. substituting the given values of intrinsic impedance and distance between plates and width of the plates, intrinsic impedance is 62.833Ω.

A)
Function of frequency
B)
Independent of frequency
C)
Proportional to square of frequency
D)
Inversely proportional to square of frequency

Correct Answer :   Function of frequency

Explanation : The wave impedance of a parallel plate waveguide in TM mode is β/k which is a function of frequency. The wave impedance is real for f>fC and purely imaginary for f<fC.

A)
Complex
B)
Real
C)
Imaginary
D)
Can Not Say

Explanation : The phase velocity and guide wavelength for a parallel plate waveguide are defined only for propagating modes. Propagating modes are those modes for which β are always positive. Hence β is always real for a parallel plate waveguide.

A)
20 mm
B)
40 mm
C)
60 mm
D)
80 mm

Explanation : The cutoff wavelength of a TMn mode in a parallel plate waveguide is 2d/n, where d is the distance between the plates and n signifies the mode of operation. For the given condition, substituting the given values, cut off wavelength is 40 mm.

A)
TM3 mode
B)
TM2 mode
C)
TM1 mode
D)
TM0 mode

Explanation : The mode of propagation for which the cutoff wavelength for wave propagation is maximum is called dominant mode. In TM mode of propagation, TM0 mode is similar to TEM mode of propagation. Hence, TM1 mode is the dominant mode.

A)
Power flow occurs in â€˜zâ€™ direction
B)
No power flow occurs in any direction
C)
Wave propagation in z direction is not possible in any mode
D)
No real power flow occurs in the â€˜zâ€™ direction

Correct Answer :   No real power flow occurs in the â€˜zâ€™ direction

Explanation : The superposition of the two plane waves in Z direction is such that complete cancellation occurs at y=0 and y=d, to satisfy the boundary conditions that Ez=0 at these planes. As f decrease to fc, β approaches 0 so that θ approaches 90â°. The two plane waves are then bouncing up and down, with no motion in +z direction, and no power flow occurs in the z direction.

A)
K/Î²
B)
Zero
C)
Imaginary
D)
Non-existing

Explanation : Wave impedance of a parallel plate waveguide for TEN modes is k/β. This expression is valid and real only for propagating modes. For non propagating modes, impedance becomes imaginary.

A)
Open two wire
B)
Coaxial
C)
Both (A) and (B)
D)
None of the above

Explanation : Since fields are confirmed within a coaxial cable it is non-radiating.

A)
TWT
B)
Klystron amplifier
C)
Klystron oscillator
D)
None of the above

Explanation : In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

The velocity of wave propagation along the helix structure is less than velocity of light.

The beam and wave travel along the structure at the same speed.

Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

The main features of TWT are :

1. Frequency range - 0.5 GHz to 90 GHz

2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

A)
C
B)
L
C)
R
D)
G

Explanation : Shunt conductance can be neglected in most of calculations.

A)
apple gate diagram
B)
bunching diagram
C)
asynchronous diagram
D)
velocity modulation diagram

Correct Answer :   apple gate diagram

Explanation : Applegate diagram is distance time plot.

A)
capacitance
B)
inductance
C)
L and C in series
D)
L and C in parallel

Correct Answer :   L and C in series

Explanation : A quarter wave line o.c. at far end behaves as a series tuned circuit.

A)
varying the beam current
B)
varying the voltage which controls beam velocity
C)
changing the rate of thermionic emission
D)
both by varying the beam current and by light varying the voltage which controls beam velocity

Correct Answer :   varying the voltage which controls beam velocity

Explanation : It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

The growing RF wave travels in opposite direction to the electron beam.

The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

It features are :

1. Frequency range - 1 GHz to 1000 GHz.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

It is used as signal source in transmitters and instruments.

A)
0.21 m
B)
2.1 m
C)
2.98 m
D)
29.8 m

46 .
In the given figure the time taken by the wave to make one round trip is
A)
10 ns
B)
20 ns
C)
30 ns
D)
40 ns

Explaination :

A)
B)
oxidation
C)
photo etching
D)
printed circuit technique

Correct Answer :   printed circuit technique

Explanation : Printed circuit techniques is used for micro strip line.

A)
there will be no oscillations on line
B)
there will be only 1 or 2 oscillations on line
C)
there will be a finite number of oscillations on line
D)
the oscillations will continue indefinitely

Correct Answer :   the oscillations will continue indefinitely

Explanation :

A)
B)
C)
D)

Explanation :

50 .
A matched generator (Zg = Z0) with 1 Ω available. If all ports are matched, the power delivered at ports 1, 2, 3 respectively are
A)
0.33 W each
B)
0 W, 0 W, 1 W
C)
0.5 W, 0.5 W, 0 W
D)
0 W, 0.25 W, 0.25 W

Correct Answer :   0.5 W, 0.5 W, 0 W

Explaination :

Since all ports matched, input SWR = 1. No power is reflected and Pin = P4 = 1 W.

This power splits between ports 1 and 2. Therefore P1 = P2 = 0.5 Ω, P3 = 0.

A)
90Â° out of phase with each other
B)
45Â° out of phase with each other
C)
in phase
D)
in phase opposition

Correct Answer :   90Â° out of phase with each other

Explanation : Since the two wire radiators are at 90° to each other, they have to be excited 90° out of phase with each other.

A)
LP filter
B)
HP filter
C)
Bandpass filter
D)
Band stop filter

Explanation : It allows high frequencies.

A)
guide diameter
B)
cube of guide diameter
C)
square of guide diameter
D)
square root of guide diameter

Explanation :

Some applications require dual polarization capability. Circular waveguide has this capability.

These analysis uses cylindrical coordinates.

In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode.

If D is diameter of waveguide

λc = 1.706 D for TE11 mode

λc = 1.029 D for TE21 mode

λc = 0.82 D for TE01 mode

λc = 1.306 D for TM01 mode.

A)
square of cross-sectional area
B)
cube root of cross-sectional area
C)
square root of cross-sectional area
D)
its cross-sectional area

Correct Answer :   its cross-sectional area

Explanation :

A)
anode, buncher cavity, catcher cavity, cathode
B)
anode, catcher cavity, cathode, buncher cavity
C)
cathode, buncher cavity, catcher cavity, cavity
D)
cathode, catcher cavity, anode, buncher cavity

Correct Answer :   cathode, buncher cavity, catcher cavity, cavity

Explanation : Cathode is the first part and anode is the last.

A)
SONAR
B)
LORAN
C)
Fathometer
D)
Echosounder

A)
1 GHz
B)
10 GHz
C)
100 GHz
D)
100 MHz

A)
Improve the target bearing resolution
B)
Reduce interference from the effects of sea return
C)
Increases receiver sensitivity for echoes from targets
D)
Vary the pulse frequency in order to control the maximum target

Correct Answer :   Reduce interference from the effects of sea return

A)
Small reflector
B)
Nearer reflector
C)
Further reflector
D)
Large reflector

A)
Towards the earth
B)
Away from the earth
C)
Towards the outer space
D)
Towards the ionosphere

Correct Answer :   Towards the earth

A)
10 to 10000 MHz
B)
30 to 30000 MHz
C)
300 to 3000 MHz
D)
3000 to 30000 MHz

Correct Answer :   3000 to 30000 MHz

A)
Circular wave guide
B)
Surface wave guide
C)
Co-axial cable
D)
Rectangular wave guide

Explanation : 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.

A)
[I] = [Z][V]
B)
[V] = [Z][I]
C)
[Z] = [V][I]
D)
[V] = [Z]-[I]

Correct Answer :   [V] = [Z][I]

Explanation : 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.

A)
[I] = [Z] [V]
B)
[I] = [Y] [V]
C)
[Y] = [V] [I]
D)
[V] = [Z]-1[I]

Correct Answer :   [I] = [Y] [V]

Explanation : 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.

A)
Real
B)
Complex
C)
Rational
D)
Purely imaginary

Explanation : 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.

A)
Symmetric matrix
B)
Null matrix
C)
A unit matrix
D)
Skew symmetric matrix

Explanation : 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.

A)
Voltage and current
B)
Impedance at different ports
C)
Indecent and the reflected voltage waves
D)
None of the above

Correct Answer :   Indecent and the reflected voltage waves

Explanation : S matrix can be used to represent any n port network. S parameters are defined for microwave networks. Hence instead of voltage and current measurement, the amplitude of the incident and reflected voltage waves is measured.

A)
[v-] = [s] [v+].
B)
[s] = [v] [v-].
C)
[v-] [v] = [s].
D)
[v+] = [s] [v-].

Correct Answer :   [v-] = [s] [v+].

Explanation : S parameter for a microwave network is defined as the ratio of reflected voltage wave to the incident voltage wave. When represented in the form of a matrix, reflected voltage matrix is the product of S parameter and the incident voltage wave at that port.

A)
CRO
B)
Network analyzer
C)
Circulator
D)
Attenuator

Explanation : Network analyzer is a device to which any microwave network can be externally connected with the help of probes and the s parameters of the network can be obtained.

A)
Unitary
B)
Skew symmetric
C)
Identity matrix
D)
Symmetric

Explanation : For a reciprocal network, the input to port I and output at port j is the same as the input at port j and output measured at port i. Hence, the ports are interchangeable. As the ports are interchangeable, this is reflected in the matrix and the matrix becomes symmetric.

A)
Symmetric
B)
Unitary
C)
Identity matrix
D)
Null matrix

Explanation : For a lossless network, the scattering matrix has to be unitary. That is, the law of conservation of energy is to be verified for this case. Using appropriate formula, this condition can be verified.

A)
0.15 dB
B)
6.5 dB
C)
6.020 dB
D)
10 dB

Explanation : Given the reflection coefficient of the network, return loss of the network is calculated using the formula -20 log â”‚Ð“â”‚. Substituting for reflection coefficient, the return loss of the network is 6.02 dB.

A)
12.05 dB
B)
10 dB
C)
20 dB
D)
0.15 dB

Explanation : Given the reflection coefficient of the network, return loss of the network is calculated using the formula -20 log â”‚Ð“â”‚. Substituting for reflection coefficient, the return loss of the network is 12.05 dB.

A)
To represent a 2 port network
B)
To represent a 2 port network
C)
To represent the impedance of a microwave network
D)
When there is two or more port networks in the cascade

Correct Answer :   When there is two or more port networks in the cascade

Explanation : The Z, Y, and S parameter representation can be used to characterize a microwave network with an arbitrary number of ports. But most microwave networks consist of cascade of two or more two port networks. In this case it is convenient to use ABCD matrix for network representations.

A)
Sum of the ABCD matrices representing the individual two ports
B)
Product of ABCD matrices representing the individual two ports
C)
Difference of the ABCD matrices representing the individual two ports
D)
Sum of transpose of ABCD matrices representing the individual two ports

Correct Answer :   Product of ABCD matrices representing the individual two ports

Explanation : When two networks are connected in cascade, each of the two networks are represented as a 2×2 square matrix. Then to obtain the equivalent matrix of the cascade, the product of the ABCD matrices of each stage is taken.

A)
A=0, B=1, C=1, D=0
B)
A=1, Z=B, C=0, D=1
C)
A=Z, B=1, C=1, D=0
D)
A=1, B=0, C=Z, D=1

Correct Answer :   A=1, Z=B, C=0, D=1

Explanation : If simple impedance or an equivalent impedance of a network is represented as a ABCD matrix, writing the equations in terms of voltage and current and setting each variable to zero, the four constants are obtained. For an impedance Z, the constants are A=1, Z=B, C=0, D=1.

A)
A=1, B=0, C=Y, D=1
B)
A=1, B=0, C=Z, D=1
C)
A=1, Y=B, C=0, D=1
D)
A=Z, B=1, C=1, D=0

Correct Answer :   A=1, B=0, C=Y, D=1

Explanation : If simple admittance or an equivalent admittance of a network is represented as a ABCD matrix, writing the equations in terms of voltage and current and setting each variable to zero, the four constants are obtained. For an admittance Y, the constants are A=1, Z=B, C=0, D=1.

A)
4.7
B)
3.2
C)
2
D)
0.5

Explanation : Z11 parameter of a two port network is the ratio of the A parameter of the network to the B parameter of the network. Taking the ratio of the given values, Z11 is 2.

79 .
For a 2 port network, if the admittance parameter Yâ‚â‚‚=0.4, then B among the ABCD, parameters for the 2 port network is
A)
2.5
B)
4.5
C)
5.5
D)
6.5

Explaination : For a two port network, B parameter is defined as the reciprocal of the admittance Y12. Taking the reciprocal of the given value, the B parameter of the network is 2.5.

A)
Gain in the resonant circuit
B)
Electric energy stored in the circuit
C)
Loss in the resonant circuit
D)
Magnetic energy stored in the circuit

Correct Answer :   Loss in the resonant circuit

Explanation : Quality factor of a resonant network is defined as the ratio of average energy stored to the energy loss/ second. Hence, lower loss implies a higher quality factor.

81 .
The relation between unloaded Q and external Q is:
A)
B)
C)
D)
None of the above

Explaination : To compute unloaded Q only the resistance in the resonant circuit is considered. But to calculate external Q, the resistance and other load in the external load is also considered. Sine Q and R are inversely proportional, as R increases Q decreases. Since R is greater for external Q computation, unloaded Q> external Q.

A)
200
B)
100
C)
0.5
D)
0.005

Explanation : The relation between quality factor and bandwidth is given as bandwidth=Q-1. Substituting for bandwidth in this expression, the quality factor of the resonant circuit is 0.005.

83 .
If a parallel RLC circuit is excited with a source of 8v, 50 Hz and the circuit has an inductor of 1mH, capacitor of 1µF and a resistor of 50Ω, then the power loss that occurs in the circuit is:
A)
6.4mW
B)
3.2mW
C)
12.8mV
D)
None of the above

Explaination : The power loss in a parallel RLC circuit is 0.5â”‚Vâ”‚2/R. given the values of source voltage and resistance in the circuit, the power loss in the parallel RLC circuit is 6.4mW.

A)
True
B)
False
C)
Can Not Say
D)
None of the above

Explanation : Band width and quality factor of a series RLC circuit are both inversely related. Higher the quality factor, lower the operating bandwidth.

A)
shorted at both the ends
B)
open at both the ends
C)
matched at both the ends
D)
None of the above

Correct Answer :   shorted at both the ends

Explanation : A cylindrical cavity resonator is formed by shorting both the ends of the cylindrical cavity because open ends may result in radiation losses in the cavity.

A)
151
B)
161
C)
181
D)
216

Explanation : Wave number for a circular cavity resonator is given by the expression 2πf011√∈r/C. substituting the given values in the above expression; the wave number of the cavity resonator is 151.

A)
560
B)
1350
C)
1560
D)
2500

Explanation : Unloaded Q due to the dielectric loss in a circular cavity resonator is the reciprocal of the loss tangent. Hence, taking the reciprocal of the loss tangent, unloaded Q due to dielectric loss is 2500.

88 .
A circular cavity resonator has a wave number of 151, radius of 2.74 cm, and surface resistance of 0.0184Ω. If the cavity is filled with a dielectric of 2.01, then unloaded Q due to conductor loss is:
A)
21460
B)
25490
C)
29390
D)
None of the above

Explaination : Unloaded Q of a circular resonator due to conductor loss is given by ka/2Rs. is the intrinsic impedance of the medium. Substituting the given values in the equation for loaded Q, value is 29390.

89 .
If unloaded Q due to conductor loss and unloaded Q due to dielectric loss is 29390 and 2500 respectively, then the total unloaded Q of the circular cavity is:
A)
2300
B)
2500
C)
29390
D)
31890

Explaination : The total unloaded Q of a circular cavity resonator is given by the expression (Qc-1+ Qd-1)-1. Substituting the given values in the above expression, the total unloaded Q for the resonator is 2300.

A)
Î²/Î±
B)
Î²/2Î±
C)
2Î²/Î±
D)
Z0/ZL

Explanation : Quality factor of a short circuited transmission line is a function of attenuation constant and phase constant of the transmission line. Higher is the attenuation in the transmission line, lower is the quality factor of the transmission line.

91 .
If the attenuation due to dielectric loss and attenuation due to conductor loss in a microstrip transmission line is 0.024Np/m and 0.0724 Np/m, then the unloaded quality factor if the propagation constant is 151 is:
A)
150
B)
234
C)
587
D)
783

Explaination : Unloaded Q for a microstrip line is given by β/2α. Α is the sum of attenuation due to conductor loss and dielectric loss. Substituting the given values the equation, unloaded Q is 783.

92 .
A microstrip patch antenna has a width of 5.08mm and surface resistivity of 1.84*10-2. Then the attenuation due to conductor loss is:
A)
0.02
B)
0.034
C)
0.054
D)
0.0724

Explaination : Attenuation due to conductor loss of a microstrip line is given by Rs/Z0W. Substituting the given values, attenuation due to conductor loss is 0.0724 Np/m.

93 .
A coaxial cable is air filled with air as dielectric with inner and outer radius equal to 1 mm and 4 mm. If the surface resistivity is 1.84*10-2Ω,then the attenuation due to conductor loss is :
A)
0.011
B)
0.022
C)
0.11
D)
0.22

Explaination : Conductor loss in a coaxial cable is given by Rs(a-1+b-1)/2ln (b/a). Here ‘a’ and ‘b’ are the inner and outer radii of the coaxial cable. is the intrinsic impedance of the medium, for air is 377Ω. Substituting the given values in the equation, conductor loss is 0.022 Np/m.

94 .
An air coaxial cable has attenuation of 0.022 and phase constant of 104.7, then the quality factor of a λ/2 short circuited resonator made out of this material is:
A)
1218
B)
1416
C)
2380
D)
Insufficient data

Explaination : Quality factor of a λ/2 short circuited transmission line is β/2α. β is the phase constant and α is the attenuation constant of the line, substituting the given values, the quality factor of the transmission line is 2380.

A)
voltage coefficient
B)
reflection coefficient
C)
coupling coefficient
D)
power transfer coefficient

Explanation : Coupling coefficient tells how the resonator is coupled to the external circuitry. A resonator can be coupled in three ways. They can be under coupled, critically coupled or over coupled.

A)
zero frequency
B)
cutoff frequency
C)
resonant frequency
D)
None of the above

Explanation : In order to obtain a maximum power transfer between a resonator and a feed line, the resonator should be matched to the feed line at the resonant frequency of the resonator which is coupled.

A)
critically coupled
B)
over coupled
C)
under coupled
D)
None of the above

Explanation : The resonator is critically coupled to the feed line when the coupling coefficient is 1. Maximum power is transferred between the resonator and the feed line since the resistance of the resonator is equal to the characteristic impedance of the transmission line.

A)
series inductance
B)
shunt inductance
C)
shunt capacitance
D)
series capacitance

Explanation : In aperture coupling, a small aperture is made in the transverse wall of the cavity which is to be coupled to an external microwave circuit. This aperture made in the transverse wall of the cavity acts as a shunt inductance.

A)
TE mode of resonance
B)
TM mode of resonance
C)
TEM mode of resonance
D)
TE, TM modes of resonance

Correct Answer :   TE, TM modes of resonance

Explanation : 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.

A)
Ampereâ€™s law
B)
Helmholtz equation
C)
Gaussian equation
D)
None of the above

Explanation : 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.

A)
Defined as the ratio of stored energy to the power dissipated in the walls
B)
Defined as the ratio of length of the waveguide to breadth of the waveguide
C)
Both (A) and (B)
D)
None of the above

Correct Answer :   Defined as the ratio of stored energy to the power dissipated in the walls

Explanation : 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.

A)
140.4
B)
145.2
C)
157.08
D)
415.08

Explanation : 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.

A)
1250
B)
1800
C)
2450
D)
2500

Explanation : 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.

104 .
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)
1.8 cm
C)
2.20 cm
D)
2.8 cm

Explaination : 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.

105 .
Given the dimension of the waveguide as b<a<d, no resonant mode exists for this specification of dimensions.
A)
True
B)
False
C)
Can Not Say
D)
None of the above

Explaination : For the given dimensional specification b<a<d, the dominant resonant mode (lowest resonant frequency) will be the TE101 mode, corresponding to the TE10 dominant waveguide mode in a shorted guide of length λg/2.

A)
True
B)
False
C)
Can Not Say
D)
None of the above

Explanation : 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.

A)
zero potential
B)
negative potential
C)
low positive potential
D)
high positive potential

Explanation : It uses a single cavity resonator for generating microwave oscillations.

Its parts are electron gun, resonator, repeller and output coupling.

It operates on the principle of positive feed back.

The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.

This positive feedback supports oscillations. Its feature are :

1. Frequency range - 2 to 100 GHz

2. Power output - 10 MW to about 2 W

3. Efficiency - 10 - 20 %

Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.

A)
an inductance and capacitance in parallel
B)
an inductance
C)
a capacitance
D)
an inductance and capacitance in series

Correct Answer :   an inductance and capacitance in parallel

Explanation : A quarter wave line short-circuited at far end behaves as a parallel tuned circuit.

A)
2Â°
B)
5Â°
C)
50Â°
D)
100Â°

Explanation :

A)
Gunn diode
B)
BARITT diode
C)
IMPATT diode
D)
Step recovery diode

Explanation : A Gunn diode uses GaAs which has a negative differential mobility, i.e., a decrease in carrier velocity with increase in electric field.

This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.

A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.

A)
Aid in calibrating the display unit
B)
Prevent frequency drift in the klystron
C)
Both (A) and (B)
D)
Allow the transmitter and the receiver to operate from a common antenna

Correct Answer :   Allow the transmitter and the receiver to operate from a common antenna

A)
Density modulation at the input cavity creates velocity modulation at the output cavity
B)
Velocity modulation at the input cavity creates density modulation at the output cavity
C)
Phase modulation at the input cavity creates velocity modulation at the output cavity
D)
Frequency modulation at the input cavity creates velocity modulation at the output cavity

Correct Answer :   Velocity modulation at the input cavity creates density modulation at the output cavity

A)
Its resonant cavity
B)
The repeller voltage
C)
Its mode of operation
D)
The accelerating voltage

Correct Answer :   Its resonant cavity

114 .
Which of the following permits a microwave signal to travel in one direction with virtually no loss, but severely attenuates any signal attempting to travel in the reverse direction?
A)
Isolator
B)
Circulator
C)
Wave trap
D)
Tunnel diode

A)
B)
C)
D)

A)
1 to 100 GHz
B)
1 to 500 MHz
C)
10 to 1000 GHz
D)
1000 to 10,000 GHz

Correct Answer :   1 to 100 GHz

A)
Thyratron tube
B)
Tunnel diode
C)
Klystron tube
D)
Both (B) and (C)

Correct Answer :   Both (B) and (C)

A)
Modulation
B)
C)
Attenuation
D)
Propagation

A)
Klystron
B)
Magnetron
C)
Thyratron
D)
Reflex-klystron

A)
far end
B)
source end
C)
midway between source and far end
D)
None of the above

Explanation : When a line is short-circuited at far end, the voltage at far end is zero.

A)
20 dB more
B)
20 dB less
C)
100 dB less
D)
700 dB more

Correct Answer :   20 dB more

Explanation : As frequency increases, transmission loss increases slightly.

A)
at a velocity that is about 50% of speed of light
B)
at a velocity that is almost equal to speed of light
C)
at a velocity that is a small fraction of speed of light
D)
at a velocity that may be even more than speed of light

Correct Answer :   at a velocity that is a small fraction of speed of light

Explanation : In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

The velocity of wave propagation along the helix structure is less than velocity of light.

The beam and wave travel along the structure at the same speed.

Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

The main features of TWT are :

1. Frequency range - 0.5 GHz to 90 GHz

2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

A)
cutoff frequency for TE10 and TE01 modes are different
B)
cutoff frequency for TE10 and TE01 modes are same
C)
cutoff frequency for TE10 mode = haf the cutoff frequency for TE20 mode
D)
cutoff frequency for TE10 mode = twice the cutoff frequency for TE20 mode

Correct Answer :   cutoff frequency for TE10 and TE01 modes are same

Explanation : When a circular waveguide is rotated by 90°, the configuration remain the same.

A)
SWR = 0
B)
SWE = 0
C)
SWR = âˆž
D)
SWR is finite

Correct Answer :   SWR is finite

A)
B)
C)
D)

A)
to change mode of wave transmission
B)
to suppress modes with higher cut off frequencies
C)
to suppress modes with lower cut off frequencies
D)
Both (A) and (B)

Correct Answer :   Both (A) and (B)

A)
pulses with very small width
B)
pulses with very large width
C)
pulses whose width is neither small nor large
D)
Either (B) or (C)

Correct Answer :   pulses with very small width

Explanation : High speed means time period is small. Therefore pulses should also have small width.

A)
balun
B)
slotted line
C)
directional coupler
D)
Î»/4 transformer

Explanation : A balun gives 4 : 1 impedance transformation.

A)
high SWR at both ports
B)
high SWR at input port and low SWR at output port
C)
low SWR at both ports
D)
low SWR at input port and high SWR at output

Correct Answer :   low SWR at both ports

Explanation : Turn ratio is so selected as to give low SWR at both ports.

A)
proportional to wavelength
B)
inversely proportional to wavelength
C)
proportional to square of wavelength
D)
inversely proportional to square of wavelength

Correct Answer :   inversely proportional to square of wavelength

A)
couple two antennas to a transmitter
B)
isolate the antenna from the local oscillator
C)
prevent interference between two antennas connected to receiver
D)
use an antenna for reception or transmission without interference

Correct Answer :   use an antenna for reception or transmission without interference

Explanation : Same antenna is used for transmission and reception.

A)
progresses only in forward direction
B)
progresses only in backward direction
C)
travelling along the line winds itself back and forth
D)
None of the above

Correct Answer :   travelling along the line winds itself back and forth

Explanation : It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

The growing RF wave travels in opposite direction to the electron beam.

The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

It features are :

1. Frequency range - 1 GHz to 1000 GHz.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

It is used as signal source in transmitters and instruments.

A)
TR tubes
B)
ATR tube
C)
Both TR and ATR tube
D)
None of the above

Correct Answer :   Both TR and ATR tube

Explanation : A branched duplexer funds use in narrow bandwidth applications.

TR tube stands for transmit-receive tube and ATR tube stands for antitransmit receive tube.

Both these tubes are used in branched duplexer.

A)
low noise
B)
very high gain
C)
D)
Both (B) and (C)

Explanation : Since reactance does not contribute thermal noise to the circuit, it is a low noise device.

A)
low frequencies
B)
high frequencies
C)
Both (A) and (B)
D)
frequencies which are neither very low nor very high

Explanation : At high frequencies transit time is large as compared to the period of microwave signal.

A)
100 watts
B)
1,000 watts
C)
10,000 watts
D)
1,000,000 watts

137 .
If the duration of the radar transmitted pulse, on a particular range of operation, is increased, the required bandwidth of the receiver’s IF amplifiers
A)
Must be doubled
B)
May be decreased
C)
Must remain as before
D)
Must be increased

Correct Answer :   Must be increased

A)
The dimension of each cavity resonator
B)
The number of the cavity resonators
C)
The flux density of the external magnet
D)
The ratio of the dc cathode voltage to the magnetic flux density

Correct Answer :   The dimension of each cavity resonator

A)
To the tone of the pulse repetition
B)
Tune the magnetron to the correct frequency
C)
Which may be used to tune the radar synchronizer
D)

A)
The AFC system
B)
Varying the repeller voltage
C)
Adjusting the flexible wall of the resonant cavity
D)

A)
a hollow metallic enclosure
B)
a hollow enclosure having magnetic material as its walls
C)
a hollow enclosure having dielectric material as its walls
D)
None of the above

Correct Answer :   a hollow metallic enclosure

Explanation : Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field.

These enclosures are called cavity resonators.

A)
at low frequencies
B)
at microwave frequencies
C)
at frequencies used in AM broadcast
D)
Both (B) and (C)

Correct Answer :   at microwave frequencies

Explanation : Atomic and molecular distances are very small. Therefore resonance can occur only at microwave frequencies.

A)
Gunn diode
B)
PIN diode
C)
Tunnel diode
D)
Varactor diode

Explanation : A PIN diode has an intrinsic (i) layer between p and n layers. When reverse bias is applied depletion layers are formed at p-i and i-n junctions.

The effective/width of depletion layer increases by the width of i layer. It can be used as a voltage controlled attenuator.

At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer.

This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.

A)
0.47 dB/m
B)
0.54 dB/m
C)
4.7 dB/m
D)
5.4 dB/m

Explanation : 0.054 x 8.68 = 0.47 dB/m.

A)
one cavity resonator
B)
two cavity resonators
C)
three cavity resonators
D)
None of the above

Correct Answer :   one cavity resonator

Explanation : It uses a single cavity resonator for generating microwave oscillations.

Its parts are electron gun, resonator, repeller and output coupling.

It operates on the principle of positive feed back.

The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.

This positive feedback supports oscillations.

Its feature are :

1. Frequency range - 2 to 100 GHz

2. Power output - 10 MW to about 2 W

3. Efficiency - 10 - 20 %

Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.

A)
1 Î¼ H/m
B)
10 Î¼ H/m
C)
0.1 Î¼ H/m
D)
0.01 Î¼ H/m

Correct Answer :   0.1 Î¼ H/m

Explanation :

A)
short circuit
B)
open circuit
C)
complex impedance
D)
Either (A) or (B)

Correct Answer :   Either (A) or (B)

Explanation :

A)
5
B)
10
C)
50
D)
200

Explanation : A TV channel has a bandwidth about 5 MHz. Hence 300 MHz spectrum can accommodate about 50 channels.

149 .
In the given figure the E and H lines in a coaxial cable
A)
The directions of E and H lines are wrong
B)
Radial lines are H lines and circular lines are E lines
C)
The radial lines are E lines and circular lines are H lines
D)
Radial lines may be E and H lines depending an direction of current

Correct Answer :   The radial lines are E lines and circular lines are H lines

Explaination : H lines are concentric circles around conductor and E lines are radial.

A)
B)
C)
D)

Explanation : Time required for microwave cooking is much less than the time required for conventional cooking.

A)
2
B)
4
C)
8
D)
16

Explanation :

Range = (power)025.

A)
low power device
B)
high power device
C)
high efficiency device
D)
Both (A) and (B)

Correct Answer :   low power device

Explanation : It uses a single cavity resonator for generating microwave oscillations.

Its parts are electron gun, resonator, repeller and output coupling.

It operates on the principle of positive feed back.

The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.

This positive feedback supports oscillations.

Its feature are :

1. Frequency range - 2 to 100 GHz

2. Power output - 10 MW to about 2 W

3. Efficiency - 10 - 20 %

Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.

A)
a half wave line
B)
a quarter wave line
C)
a short circuited stub
D)
an open circuited stub

Correct Answer :   a quarter wave line

Explanation : Impedance inversion occurs when load impedance is not matched with characteristic impedance of line.

A)
causes retardation of all electrons
B)
causes acceleration of some electrons and retardation of others
C)
more than 30 dB
D)
None of the above

Correct Answer :   more than 30 dB

Explanation : A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

A)
Loran D: 10.2 kHz
B)
Loran C: 100 kHz
C)
Loran B: 900 kHz
D)
Loran A: 1950 kHz

Correct Answer :   Loran C: 100 kHz

A)
The duty cycle
B)
The width of the transmitted pulses
C)
The bandwidth of the receiver IF stages
D)
The interval between transmitted pulses

Correct Answer :   The interval between transmitted pulses

A)
Must have its battery replaced after emergency use
B)
Must be capable of floating or being secured to a survival
C)
May be tested during the first five minutes of any hour
D)
All of the above

Correct Answer :   All of the above

158 .
A thin layer of dirt and grime coverts the reflecting surface of the parabolic dish of a radar set. The particular effect on the performance of the radar will be
A)
A decrease in range
B)
A decrease in gain
C)
No noticeable effect
D)
A reduction in horizontal resolution

Correct Answer :   No noticeable effect

A)
B)
C)
D)
Random Doppler shift

A)
The effect of an external magnetic field
B)
The energy liberated form the collector
C)
The absorption of energy by the signal from an electron stream
D)
The energy contained the cavity resonators

Correct Answer :   The absorption of energy by the signal from an electron stream

161 .
Consider the following statements

1. Bunching of electrons occurs in two cavity klystron amplifier.
2. Bunching of electrons occurs in multi cavity klystron amplifier.
3. Bunching of electrons occurs in reflex cavity klystron amplifier.

Which of the above statements are correct?
A)
1 and 2 only
B)
1, 2 and 3
C)
1 and 3 only
D)
2 and 3 only

Correct Answer :   1, 2 and 3 only

Explaination : A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

A)
Gunn diode
B)
Tunnel diode
C)
Impatt diode
D)
Varactor diode

Explanation : Gunn diode, Tunnel diode and Impatt diodes are negative resistance devices.

The limitation of solid state devices at high frequencies include those associated with transit time and junction capacitances.

The devices used are : Transferred electron oscillators (Gunn diode), Avalanche diode oscillators (Impatt diode, Trapatt diode, Masters, Lasers, Tunnel diode, Varactor etc).

A)
coplanar arms are coupled
B)
E and H arms are decoupled
C)
all ports are perfectly matched
D)
A signal into coplanar arm splits equally between E and H arms

Correct Answer :   coplanar arms are coupled

Explanation : Coplanar arms are decoupled.

A)
a balun
B)
double stub
C)
D)
a single stub of adjustable position

Explanation : Double stub is useful for matching over a range of frequencies.

A)
because of atmospheric attenuation
B)
because of output tube power limitation
C)
because of earth's curvature
D)
to ensure that applied dc voltage is not excessive

Correct Answer :   because of earth's curvature

Explanation : Earth's curvature limits the distance between microwave links.

A)
1
B)
0.1
C)
0.01
D)
0.001

Explanation :

1 x 10-6 x 1000 = 0.001.

A)
Reflex klystron amplifier
B)
Two cavity klystron amplifier
C)
Multi-cavity klystron amplifier
D)
All of the above

Correct Answer :   Reflex klystron amplifier

Explanation : A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

A)
is more than avalanche breakdown voltage
B)
is less than avalanche breakdown voltage
C)
may be more or less than a avalanche breakdown voltage
D)
is very high as compared to avalanche breakdown voltage

Correct Answer :   is less than avalanche breakdown voltage

Explanation : The action of varactor diode is due to the capacitance of depletion layer. The thickness of depletion layer depends on the reverse bias which should not cause breakdown.

A)
2
B)
12
C)
0.707
D)
0.5

A)
gain and coupling
B)
gain and isolation
C)
gain and directivity
D)
coupling and directivity

Correct Answer :   coupling and directivity

A)
10
B)
50
C)
150
D)
1500

172 .
A 75 ohm line is first short terminated and minima locations are noted. Then the short is replaced by resistive load and minima location are again noted. If minima location are not altered and VSWR is 3, the value of resistive load is
A)
25 Ω
B)
50 Ω
C)
225 Ω
D)
250 Ω

Explaination :

A)
B)
long range TV transmission
C)
long range cable transmission
D)
Both (A) and (B)

A)
(PRF)/(pulse width)
B)
(PRF) (pulse width)
C)
(pulse width)/(PRF)
D)
(pulse width) + (PRF)

Correct Answer :   (PRF) (pulse width)

175 .
A TEâ‚â‚€ rectangular waveguide is to be designed for operation over 25-35 GHz and the band centre is 1.5 times the cutoff frequency. The dimension of broadside is
A)
15 mm
B)
10 mm
C)
9 mm
D)
7.5 mm

A)
causes retardation of all electrons
B)
causes acceleration of all electrons
C)
causes acceleration of some electrons and retardation of others
D)
None of the above

Correct Answer :   causes acceleration of some electrons and retardation of others

Explanation : A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

A)
0.2 Î¼ H/m
B)
0.6 Î¼ H/m
C)
1.6 Î¼ H/m
D)
10 Î¼ H/m

Correct Answer :   1.6 Î¼ H/m

A)
one resonant frequency
B)
n resonant frequencies
C)
n/2 resonant frequencies
D)
Either (B) or (C)

Correct Answer :   n resonant frequencies

A)
B)
C)
D)

A)
decreases
B)
increases
C)
is not affected
D)
Either (A) or (B)

A)
TWT
B)
Magnetron
C)
Gunn diode
D)
Reflex klystron

A)
resistive
B)
inductive
C)
capacitive
D)
partly resistive and partly capacitive

A)
decreases
B)
increases
C)
is not affected
D)
Either (A) or (C)

A)
are bulky
B)
C)
are more expensive and complex
D)
do not lend themselves to printed circuit

A)
parallel to the axis of cathode
B)
inclined to the axis of cathode
C)
perpendicular to the axis of cathode
D)
Either (B) or (C)

Correct Answer :   parallel to the axis of cathode

Explanation : The operation of magnetron is based on interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at 90° with respect to each other.

In a magnetron three forces act on electron viz. force due to electric field (equal to - eE), force due to magnetic field [equal to - e (v x B)] and centrifugal force (equal to mv2/r).

The path of the electron can be found by balancing these three forces. Magnetron can be of three types i.e., negative resistance device, cyclotron frequency device and travelling wave or cavity device.

In negative resistance magnetron use is made of the negative resistance between two anode segments.

It has low efficiency and is used at frequencies less than 0.5 GHz.

In cyclotron magnetron a synchronism exists between ac component of electric field and periodic oscillation of electrons in a direction parallel to the field.

It is used for frequencies higher than 100 MHz.

A cavity magnetron has a number of cylindrical cavities in the interaction region.

The cavity magnetron is the most common type of magnetron. Its features are :

1. Frequency range - 500 MHz to 10 GHz

2. Power output - 250 kW (pulses)

It is used in radar systems, industrial heating systems and microwave ovens.

A)
silicon
B)
GaAs
C)
Either (A) or (B)
D)
Neither (A) nor (B)

Correct Answer :   Either (A) or (B)

A)
330
B)
1250
C)
2500
D)
8330

A)
Load power depends on phase constant
B)
standing waves will always exist on the line
C)
power transmission is most efficient when there are no standing waves on line
D)
power transmission is least efficient when there are no standing waves on the line

Correct Answer :   power transmission is most efficient when there are no standing waves on line

Explanation : If standing waves are not there, whole of the power is absorbed by load.

A)
is directed along the helix axis
B)
is directed radially from helix axis
C)
is inclined to the helix axis by about 45Â°
D)
is inclined to the helix axis by about 60Â°

Correct Answer :   is directed along the helix axis

Explanation : In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

The velocity of wave propagation along the helix structure is less than velocity of light.

The beam and wave travel along the structure at the same speed.

Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

The main features of TWT are :

1. Frequency range - 0.5 GHz to 90 GHz

2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

A)
6370 mi
B)
6370 km
C)
8493 mmi
D)
8493 km

A)
Duplexer stage
B)
Local oscillator
C)
Single mixer stage
D)
Transmitter oscillator

A)
Electron transit time
B)
C)
Inter-electrode capacitance
D)
Degree of emission from the cathode

Correct Answer :   Degree of emission from the cathode

A)
A high duty cycle
B)
A low repetition rate
C)
A narrow, antenna-beam width in the horizontal plane
D)
A narrow, antenna-beam width in the vertical plane

Correct Answer :   A narrow, antenna-beam width in the horizontal plane

A)
Its physical dimensions
B)
The mode of operation
C)
Its electrical dimensions
D)
The capacitor which tunes it

Correct Answer :   Its physical dimensions

A)
B)
C)
D)
Random Doppler shift

A)
Is equivalent to an LC resonant circuit
B)
Has a low Q factor for narrow operation.
C)
Produces a frequency which is independent of the cavity size.
D)
In a reflect klystron has its output taken from the reflector plate

Correct Answer :   Is equivalent to an LC resonant circuit

A)
At the collector
B)
At the collector end of the helix
C)
At the cathode end of the helix
D)
At the control grid of the electron gun

Correct Answer :   At the cathode end of the helix

198 .
What ferrite device can be used instead of duplexer of isolate microwave transmitter and receiver when both are connected to the same antenna?
A)
Simplex
B)
Isolator
C)
Magnetron
D)
Circulator

A)
Oscillation will cease
B)
The frequency will decrease
C)
Output power would increase
D)
Bunching would occur earlier in time

Correct Answer :   The frequency will decrease

A)
And FET
B)
A tunnel diode
C)
A Rochelle salts crystal
D)
A silicon crystal

Correct Answer :   A silicon crystal

A)
Depends on the formation of charge domain
B)
Operates over a positive resistance characteristic
C)
Generates frequencies which are below 100 MHz
D)
Is capable of generating continuous microwave power of the order of kilowatt

Correct Answer :   Depends on the formation of charge domain

A)
To accelerate the electron
B)
To slow down the signal on the helix
C)
To keep the electrons from spreading out
D)
To velocity modulate the electron beam

A)
3 to 6 GHz
B)
10 to 20 MHz
C)
50 to 70 MHz
D)
100 to 120 GHz

Correct Answer :   3 to 6 GHz

A)
B)
C)
D)

A)
low loss for both low level and high level signals
B)
low loss for low power signals and high
C)
high loss for both low level and high level signals
D)
high loss for low power signals and low loss for high level signal

Correct Answer :   low loss for low power signals and high

A)
the line of sight and diffraction. Zone concepts are payable
B)
the line of sight and diffraction zone concepts are not applicable
C)
line of sight concept is applicable but diffraction zone concept is applicable
D)
diffraction zone concept is not applicable but line of sight concept is not applicable

Correct Answer :   the line of sight and diffraction zone concepts are not applicable

A)
both have infinite set of TE and TM modes
B)
rectangular waveguide has infinite TE and TM modes but not the circular waveguide
C)
circular waveguide has infinite TE and TM modes but not the rectangular waveguide
D)
None of the above

Correct Answer :   both have infinite set of TE and TM modes

A)
properties of insulating material only
B)
inner and outer conductor radius only
C)
Both (A) and (B)
D)
Neither (A) nor (B)

Correct Answer :   Both (A) and (B)

A)
is lower than that of rectangular waveguide
B)
is higher than that of rectangular waveguide
C)
is almost same as that of rectangular waveguide
D)
is very small as compared to that of rectangular waveguide

Correct Answer :   is higher than that of rectangular waveguide

A)
low pass filter
B)
high pass filter
C)
band pass filter
D)
band stop filter

Correct Answer :   band stop filter

A)
Magic tee
B)
Hybrid ring
C)
E plane tee
D)
H plane tee

A)
burglar alarms
B)
detection of aircraft
C)
garage door openers
D)
All of the above

Correct Answer :   All of the above

A)
change mode of wave transmission
B)
change direction of wave transmission
C)
change polarization of wave transmission
D)
change mode, direction or polarization wave transmission

Correct Answer :   change mode, direction or polarization wave transmission

A)
PIN diode
B)
Crystal diode
C)
Backward diode
D)
Schottky barrier diode