PSU MCQs on Electromagnetics

1. An Antenna that is circularly polarized is the
a) Helical
b) Small circular loop
c) Parabolic reflector
d) Yagi-uda

Ans: Option a)

2. The standard reference antenna for the directive gain is the
a) Infinitesimal dipole
b) Isotropic antenna
c) Elementary doublet
d) Half-wave dipole

Ans: Option b)

3. Top loading is sometimes used with an antenna in order to increase
a) Effective height
b) Bandwidth
c) Beam width
d) Input Capacitance

Ans: Option a)

4. A helical antenna is used for satellite tracking because of its
a) Circular polarization
b) Maneuverability
c) Broad bandwidth
d) Good front-to-back ratio

Ans: Option a)

5. The directivity of an isotropic antenna is
a) Zero
b) Less than unity
c) Unity
d) Infinity

Ans: Option c)

6. In order to receive a vertically polarized wave the conductor of the dipole should be mounted
a) Horizontally
b) Vertically
c) At an angle of 45^o
d) None of these

Ans: Option b)

7. For a dipole antenna
a) The radiation intensity is maximum along the normal to the dipole axis
b) The current distribution along its length is uniform irrespective of the length
c) The effective length equals to its physical length
d) The input impedance is independent of the location of the feed point

Ans: Option a)

8. Two isotropic antennas are separated by a distance of two wavelengths. If both the antennas are fed with currents of equal phase and magnitude, the number of lobes in the radiation pattern in the horizontal plane is
a) 2
b) 4
c) 6
d) 8

Ans: Option d)

9. Consider the following statements:
1.Antenna radiates energy
2. An antenna is a transition device or transducer between a guided wave and free space or vice-versa
3. The resonators and transmission lines store energy
4. An antenna converts electromagnetic signal into current and vice-versa
Which of the following statements are correct?
a) 1,2 and 4 only
b) 1,2 and 3 only

c) 2,3 and 4 only
d) 1,2,3 and 4

Ans: Option a)

10. An antenna can be made more directional by
a) Increasing its diameter
b) Increasing frequency of transmission
c) either a) or b)
d) none of the above

Ans: Option c)

11. The radiation resistance of a circular loop of a turn is 0.01 Ω. The radiation resistance of five turns of such a loop will be
a) 0.002 Ω
b) 0.01 Ω
c) 0.05 Ω
d) 0.25 Ω

Ans: Option c)

12. Far field of an antenna varies with distance r as
a)     1/r
b)     1/r²

c)    1/r³

d)     1/√r

Ans: Option a)

13. Cassegrain feed is used with a parabolic antenna in order to
a) increase the gain of the system
b) Increase the beamwidth of the system
c) Reduce the size of the main reflector
d) Allow the feed to be placed at a convenient point

Ans: Option d)

14. For a plane wave propagating in an unbounded medium (free space), the minimum angle between electric and magnetic field vectors is
a) 0
b) 60
c) 90
d) 180

Ans: Option c)

15. The main difference between the operation of transmission lines and waveguides is that
a) The latter are not distributed, like transmission line
b) The former can use stubs ans quarter-wave transformers, unlike the latter
c) Transmission lines use the principal mode of propagation and therefore do not suffer from low frequency cutoff
d) Terms such as impedance matching and standing wave ratio cannot be applied to waveguides

Ans: Option c)

16. The wavelength of a wave in a waveguide 
a) is greater than in free space
b) depends only on the waveguide dimensions and the free space wavelength
c) is inversely proportional to the phase velocity
d) is directly proportional to the group velocity

Ans: Option a)

17.  A transmission line whose characteristic impedance is a pure resistance 
a) must be a lossless line
b) must be a distortionless line
c) May not be a lossless line
d) May not be a distortionless line

Ans: Option a)

18. A 300 Ω line is terminated in a load impedance of 100 + j 200 Ω. The voltage reflection coefficient is
a) 0.6325 ∟108
b) 0.7 ∟30
c) 0.27 + j 0.196
d) 0.377 ∟42.7

Ans: Option a)

19. Diffraction of electromagnetic waves 
a) is caused by reflections from the ground
b) arises only with spherical wavefronts
c) will occur when the wave pass through a large slot
d) will occur around the edge of  a sharp obstacle

Ans: Option d)

20. An electromagnetic wave incident on a perfect conductor is 
a) Entirely reflected
b) Fully transmitted
c) Partially transmitted
d) None of these
Ans: Option a)

21. Which one of the following sets of equations is independent in maxwell's equations?
a) Two curl equations
b) two divergence equations
c) Both the curl and divergence equations 
d) two curl equations combined with the continuity equation 

Ans: Option c)

22. Consider the following statements:
For electromagnetic waves propagating in free space:
1. Electric field is perpendicular to direction of propagation
2. Electric field is along the direction of propagation
3. Magnetic field is perpendicular to direction of propagation
4. Magnetic field is along the direction of propagation
Which of these statements are correct?
a) 1 and 3
b) 1 and 4
c) 2 and 3
d) 2 and 4

Ans: Option a)

23. The dominant mode in a rectangular waveguide is TE10 because this mode has
a) No attenuation
b) No cut-off
c) No magnetic field component
d) The highest cut-off wavelength

Ans: Option d)

24. 8-point charges of 1nC each are located at the corners of a cube in free space that on 1m on a side, then  at the center is
a) 0 V/m
b) 5 V/m
c) 4 V/m
d) -5 V/m

Ans: Option a)

25. A 50 Ω lossless transmission line has a pure reactance of j100 Ω as its load. The VSWR in the line is 
a) 0
b) Infinity
c) 50
d) 100 + j 100

Ans: Option b)

26. Calculate the front-to-back ratio of an antenna in dB which radiates 3 kW in its optimum direction and 500 watts in the opposite direction
a) 0.782
b) 7.782
c) -22.22
d) none of these

Ans: Option b)

27. An uniform plane wave incident normally on a plane surface of dielectric material is reflected with a VSWR of 3. What is the percentage of incident power that is reflected.
a) 10%
b) 25 %
c) 50%
d) 75%

Ans: Option b)

28. Two coaxial cables 1 and 2 are filled with different dielectric constants ϵr1 and ϵr2 respectively. The ratio of the wavelengths in the two cables λ1/ λ2 is 
a) √( ϵr1/ ϵr2)
b) √( ϵr2/ ϵr1)
c) ϵr1/ ϵr2
d) ϵr2/ ϵr1

Ans: Option b)


29. Which of the following is zero?
a) Grad div
b) Div grad
c) Curl grad
d) Curl curl

Ans: Option c)

30. Which is not an example of convection current?
a) A moving charged belt
b) Electronic movement in a vacuum tube
c) An electron beam in a television tube
d) Electric current flowing in a copper wire

Ans: Option d)

31. One of the following is not a source of magnetostatic fields
a) A dc current in a wire
b) A Permanent magnet
c) An accelerated charge
d) An Electric filed linearly changing with time

Ans: Option c)

32. Which of thse statements is not characteristic of a static magnetic field?
a) It is solenoidal
b) It is conservative
c) It has no sinks or sources
d) Magnetic flux lines are always closed

Ans: Option b)
Static magnetic field is not conservative

33. Two thin parallel wires carry currents along the same direction. The force experienced by one due to the other is
a) Parallel to the lines
b) Perpendicular to the lines and attractive
c) Perpendicular to the lines and repulsive
d) Zero

Ans: Option b)

PSU MCQs on Satellite Communication and Radar

1. Most satellites operate in the frequency range of
a) 300 MHz to 3 GHz
b) 30 MHz to 300 MHZ
c) Above 300 GHz
d) 3 GHz to 30 GHz

Ans: Option d)

2. The frequency band used by most satellite is
a) UHF
b) VHF
c) SHF
d) EHF

Ans: Option c)
Super High Frequency:  3 to 30 GHz

3. The bandwidth of a typical satellite is
a) 500 MHz
b) 900 MHz
c) 200 MHz
d) None of these

Ans: Option a)

4. For satellite communication, the frequency should be
a) Less than the critical frequency of ionosphere
b) Equal to the critical frequency of ionosphere
c) More than the critical frequency of ionosphere
d) None of these

Ans: Option c)

5. Geostationary satellites follow
a) circular path
b) elliptical path
c) inclined path
d) cycloidal path

Ans: Option b)

6. A synchronous satellite orbits the earth once in
a) 24 hours
b) 12 hours
c) 6 hours
d) 1 hour

Ans: Option a)

7. The distance of a geostationary satellite from the surface of the earth is nearly
a) 360 Km
b) 3600 Km
c) 36,000 Km
d) 3,60,000 Km

Ans: Option c)

8. Satellite sends back signals to earth by means of
a) Yagi antenna
b) chicken-mesh antenna
c) horn antenna
d) dipole antenna

Ans: Option c)
Satellite sends back signals through horn antenna

9. In satellite communication
a) Amplitude modulation is used
b) Frequency modulation is used
c) Pulse width modulation is used
d) Pulse Amplitude modulation is used

Ans: Option b)

10. Antenna elevation angle at the ground station for satellite communication is always kept above 5^o to
a) minimize the sky noise temperature
b) reduce the effect of oxygen and water vapour absorption on the antenna noise temperature
c) minimize the slant range
d) increase the visibility of the satellite

Ans: Option d)

11. For global communication, the minimum number of satellite needed is
a) one
b) three
c) seven
d) eleven

Ans: Option b)
One satellite can see "one-third" of the globe

12. FM is preferred for satellite communication because
a) satellite channel has large bandwidth and less noise
b) It gives high modulation index
c) low bandwidth is essentially required
d) Other methods of modulation will result in fading and distortion

Ans: Option a)

13. In a satellite system:
a) upward link frequency is half of downward link frequency
b) upward link frequency is greater than that of downward link frequency
c) upward link frequency is lesser than that of downward link frequency
d) upward link frequency is equal to downward link frequency

Ans: Option b)

14. A geostationary satellite
a) remains stationary in space
b) remains at a height of 1000 km above the surface of earth
c) orbits the earth with 24 hour period
d) remains always in a direction opposite to that of sun, with respect to earth

Ans: Option c)

15. Satellite communication links are preferred over sub-marine cables because
a) they are faster
b) they involve lesser cost
c) of their multiple access ability
d) none of these

Ans: Option c)

16. The satellite orbit almost invariably used with remote sensing satellite is:
a) geostationary orbit
b) geosynchronous orbit
c) sun synchronous orbit
d) Molniya orbit

Ans: Option c)

17. The beam width required for a satellite antenna for full global coverage is approximately
a) 1
b) 5
c) 18
d) 4

Ans: Option c)

18. A satellite earth station antenna having a maximum gain of 60 dB at the operational frequency is fed from a power amplifier generating 10 KW. If the feed system has a loss of 2 dB, determine earth station EIRP(Effective Isotropic Radiated Power)

a) 98dBW
b) 100 dBW
c) 89 dB
d) 98 dB

Ans: Option a)

19.  A radio communication link is to be established via the ionosphere. The virtual height at the midpoint of the path is 300 km and the critical frequency is 9 MHz. The maximum usable frequency for the link between the stations of distance 800 km assuming flat earth is
a) 11.25 MHz
b) 12 MHz
c) 15 MHz
d) 25.5 MHz

Ans: Option c)

20. If a satellite is launched at an orbital radius of twice that of a geostationary satellite, how much time will the launched satellite take to travel around the earth
a) 48 hrs
b) 12 hrs
c) 96 hrs
d) 6 hrs

Ans: Option c)

T² α r³ by kepler’s law

Since the time period of geostationary satellite is 24 hrs

(T/24)² = 2³

T  = 67.88 hrs

20. Which of the following techniques not suitable for automatic satellite tracking?
a) Monopulse
b) Step-track
c) Conical Scanning
d) Lobe switching

Ans: Option b)

21. Which of the following statements is not correct?
a) A geo-synchronous satellite remains practically stationary relative to earth antennas
b) A geo-synchronous satellite means the same thing as geo-stationary satellite
c) There is a trade-off between the cost of a communication satellite and cost of its earth stations
d) Three geo-synchronous satellites cannot give 100% global coverage.
Ans: Option d)

22. Which ionosphere layer is responsible for return of a radiation at frequency 30 MHz?
a) D
b) E
c) F
d) All the above

Ans: Option c)

23. Communication satellites are allotted bandwidth of 500 MHz. This can be increased by using
a) Frequency and Polarization re-use
b) Time division Multiplexing
c) Frequency division Multiplexing
d) Triple modular redundancy

Ans: Option a)

24. What does a link budget for satellite communication include
a) Total cost of satellite
b) Cost of satellite plus launch vehicle
c) Signal and noise levels in dB
d) Margins of error permitted

Ans: Option: c)

25. The output stage of a transponder on-board a satellite has a maximum power output of 10 watts. However, it is not operated at the maximum power output in order to
a) Conserve the available limited battery power
b) Reduce noise due to device
c) Avoid inter-modulation distortion
d) Avoid heating up of the satellite beyond a preset value

Ans: Option a)

RADAR

1) The term RADAR stands for
a) Radio direction and reflection
b) Radio waves dispatching and receiving
c) Random detection and re-radiation
d) Radio detection and ranging

Ans: Option d)

2) Frequency in UHF range propagate by means of
a) Ground waves
b) Sky waves
c) Surface waves
d) Space waves

Ans: Option d)

3) Which of the following diode is used as a detector in a RADAR?
a) Gunn Diode
b) Schottky diode
c) IMPATT diode
d) Any of the above

Ans: Option c)

4) Most of the aircraft surveillance Radars operate in
a) X-band
b) C-band
c) L-band
d) S-band

Ans: Option c)

5) In case of RADAR receiver the IF bandwidth is inversely proportional to
a) Pulse interval
b) Pulse repetition frequency
c) square root of peak transmitted power
d) Pulse width

Ans: Option d)

6) Radar detection is limited to line of sight because
a) Of curvature of the earth
b) The waves are not reflected by the ionosphere
c) Long wavelengths are used
d) Short wavelengths are used

Ans: Option a)

7) To increase the radar range of ground and surface targets to see well beyond the normal radar horizon, the electromagnetic wave propagation adopted is
a) Ionosphere scatter
b) Tropo Scatter
c) Ground wave propagation
d) Duct

Ans: Option b)

8) Troposphere scatter is used with frequencies in the following range
a) HF
b) VHF
c) UHF
d)VLF

Ans: Option c)

9)  A Radar receives an echo from a target 20 microseconds after sending the signal. The approximate range of the target is
a) 300 m
b) 3000 m
c) 600 m
d) 6000 m

Ans: Option b)

Range= cT/2 = 3x10⁸ x 20 x 10^-6/2 = 6000/2 = 3000 m

10) Which of the following can be used to improve range resolution in a Radar?
a) Short duration pulse
b) Long duration pulse
c) High frequency of operating signal
d) Increasing bandwidth

Ans: Option a)

11) In a radar system, if the peak transmitted power is increased by a factor of 16 and the antenna diameter is increased by a factor of 2, then the maximum range will increase by a factor of
a) 16
b) 8
c) 4
d) √8

Ans: Option c)

R_max α [ P_t A_e ²]^1/4

R_max α [ P_t D⁴]^1/4

[16 x 16] ^1/4=4

12) For identifying a radar target in a non-lossy medium, the range of the target is to be doubled, the RF power radiated must be increased by

a) 2 times

b) 4 times

c) 8 times

d) 16 times

Ans: Option d)

R_max α [ P_t ]^1/4

R_max α [ 16]^1/4

^{13) An Altimeter is basically} 

^{a) a CW Radar}

^{b) a FM Radar}

^{c) a Doppler Radar}

^{d) a device to indicate the direction at height}

^{Ans: Option a)}