Objective Questions on Microwave Devices for BSNL and ISRO Exams

1. An amplifier uses step recovery diode for low level noise performance in the :

a) S- band         b) C – band        c) X – band         d) L – band

1. Negative resistance region is not found in :

a) Tunnel diode                          b) Gunn diode
c) Impatt diode                           d) Backward diode

1. Diode which is used for microwave power switching, limiting and modulation is :

a) crystal diode                          b) schottky barrier diode
c) backward diode                      d) PIN diode

1. For very low power oscillators, the diode suited is :

a) Gunn b) Avalanche      c) Tunnel           d) IMPATT

1. Material in which transferred electron bulk effect is observed is:

a) Germanium                            b) Silicon
c) Gallium Arsenide                    d) Metal semiconductor junctions

1. A step recovery diode is best suited for :

a)       low order frequency multiplication
b)       high order frequency multiplication
c)       frequency addition
d)       None

1. Diode which uses a high doping level to provide a narrow junction :

a) Gunn diode                            b) Tunnel diode
c) IMPATT diode                        d) None

1. Diode in which negative resistance occurs due to the transfer of electrons to a less mobile energy level is :

a) Gunn diode                            b) Tunnel diode
c) IMPATT                                 d) None

1. Gunn diodes are made of gallium arsenide because it :

a)       has a suitable empty energy band
b)       has a lower noise
c)       has a higher ion mobility
d)       is capable of handling power densities

1. Snap off varactor is another name of :

a) PIN diode                              b) Step recovery diode
c) Avalanche diode                     d) Schottky barrier diode

1. One of the following is called hot electron diode :

a) Schottky barrier diode b) Varactor diode
c) PIN diode                              d) None

1. The noise performance of parametric amplifier is improved by:

a) cooling                                  b) using low value of resistance
c) heating                                  d) None

1. Cooling is done in a ruby maser amplifier :

a)       as it generates a lot of heat
b)       to increase bandwidth
c)       it cannot work at room temperature
d)       to improve noise performance

1. Advantage of BJT over FET at high frequencies is that :

a)       BJT are less noisy
b)       BJT lend themselves more readily to integration
c)       BJT are capable of high gains
d)       None

1. The diode which has high efficiency than IMPATT is :

a) TRAPATT diode                     b) Tunnel diode
c) Gunn diode                            d) None

1. Highest pulsed power output is obtained by :

a) Varactor        b) Gunn c) RIMPATT       d) Schottky barrier

1. For operating at the highest frequencies a microwave transistor does not require :

a) high collector voltage              b) high collector current
c) thin base                               d) large emitter area

1. The idler frequency of a non degenerate parametric amplifier having an input frequency of f_t and pump frequency of f_p is

a) f_p – f_t b) f_t c) 2f_t d) f_t – f_p

1. For providing a greater bandwidth in parametric amplifiers one can use :

travelling wave parametric amplifier
degenerate amplifiers
Non-degenerate amplifiers
None

1. A circulator is sometimes used with a parametric amplifier to :

a)       prevent noise feedback
b)       separate the signal and idler frequencies
c)       permit more efficient pumping
d)       None

1. A high ratio of pump to signal frequency is a must in non – degenerate one port parametric amplifier because this :

a)       yields a low noise figure
b)       reduced the pump power
c)       permits high frequency operation
d)       permits low frequency operation

1. An axial magnetic field and a radial electric field is used in :

a)       coaxial magnetron
b)       Reflex klystron
c)       CFA – cross field amplifier
d)       Travelling wave magnetron

1. Which one of the following cannot be used as a pulsed device:

a) CFA              b) BWO                        c) TWT              d) None

1. Vaccum tubes fail at microwave frequencies because :

a)       noise figure increases
b)       transit time becomes too short
c)       shunt capacitive reactances become too large
d)       series inductive reactances become too small

1. In microwave tubes the transit time will increase if :

a)       the electrodes are brought closer together
b)       a higher anode current is used
c)       multiple or coaxial leads are used
d)       None

1. The TWT ……. than multicavity klystron :

a)       has a greater bandwidth
b)       is more efficient
c)       has a higher number of modes
d)       produces a higher output power

1. Strapping is used in magnetron to :

a)       prevent mode jumping
b)       ensure bunching
c)       improve the phase focussing effect
d)       prevent cathode back heating

1. Helix is used in a travelling wave tube to :

a)       ensure broadband operation
b)       reduce the noise figure
c)       reduce the axial velocity of the RF field
d)       None

1. In the TWT the attenuator is used to :

a) prevent saturation                   b) increase gain
c) prevent oscillation                   d) help bunching

1. Electronically adjustable oscillating frequency over wide range is possible in :

a) coaxial magnetron                  b) dither – tuned magnetron
c) VTM                                      d) None

1. In a TWT glass tube aquadag is used to :

a) help focussing                        b) provide attenuation
c) improve bunching                   d) increase gain

1. Which is not a TWT slow wave structure :

a) coupled cavity                        b) helix
c) ring bars                                d) periodic permanent magnet

1. Match lise – I (Microwave devices) with List – 2 (application) and select the correct answer using the codes given below the lists :

List – 1                                List – 2
A. Reflex klystron          1. Wide band amplification
B. TWT                         2. Very low level amplification
C. 2-cavity klystron        3. Low Powe FM wave generation
D. MASER                    4. Frequency multiplication
Codes :
a)         A          B          C          D
1          2          3          4
b)         A          B          C          D
4          3          2          1
c)         A          B          C          D
3          4          1          2
d)         A          B          C          D
3          1          4          2

1. The semiconductor diode which can be used in switching circuits at microwave range is :

a) PIN diode                              b) Varactor diode
c) Tunnel diode                          d) Gunn diode

1. In a TWT, the phase velocity of the axial component of the RF field on the slow wave structure is kept :

a)       equal to the velocity of the electrons
b)       slightly less than the velocity of electrons
c)       slightly more than the velocity of electrons
d)       equal to the velocity of light in free space

1. The amplification in parametric amplifier used in microwave communication system is limited by :

a) type of biasing                       b) a maximum limit of 10
c) pump energy                          d) frequency of operation

1. Schottky diodes are used in wave sharing circuits because :

a)       they have a small recovery time
b)       they have a large reverse resistance
c)       they have a large forward current
d)       their peak inverse voltage is small

1. The modes in a reflex klystron :

a)       give the same frequency but different transit time
b)       result from excessive transit time across the resonator gap
c)       are caused by spurious frequency modulation
d)       are just for theoretical considerations

1. To overcome difficulties with strapping high frequencies the type of cavity structure desired for magnetron is :

a) hole and slot                          b) slot
c) rising sun                              d) vane

1. TWT is at times preferred to magnetron for used in RADAR transmitter because it :

a) is more efficient amplifier         b) has broader band
c) is less noisy                          d) is capable of larger duty cycle

1. Backward wave oscillator is based on :

a) cross field amplifier                 b) coaxial magnetron
c) travelling wave tube                 d) rising sun magnetron

1. The most serious drawback of IMPATT diode is its :

a)       low efficiency
b)       higher noise
c)       low power handling capacity
d)       inability to provide pulsed operation

1. A TRAPATT diode is preferred to an IMPATT diode because of :

a)       its higher efficiency
b)       its lower noise
c)       laser sensitivity of harmonics
d)       its larger bandwidth

1. Gallium arsenide is preferred to silicon for use in Gunn diode because it has :

a)       lower noise at high frequencies
b)       high ion mobility
c)       suitable empty energy band which silicon does not have
d)       better frequency stability

1. Gallium antimonide is prefered to germanium for use in tunnel diode since it permits :

a)       lower noise
b)       larger voltage swing
c)       better frequency stability
d)       simpler fabrication process

1. Which one of the following can be used for amplification of microwave energy :

a) Travelling wave tube                b) Manetron
c) Reflex klystron                       d) Gunn diode

1. A microstrip line of alumina substrate with er = 9 has a zero thickness strip of width. w = 3mm. Substrate thickness h = 0.5mm. Assuming TEM wave propagation and negligible fringing field, the characteristic impedance of the line will be approximately :

a) 10 ohm          b) 21 ohm          c) 26 ohm          d) 50 ohm

1. In a Gunn oscillator where the diode is operated in a tunable resonant circuit most of the sample length of the Gunn device is maintained in the negative conductance stae during most of the RF cycle for :

a) delayed domain mode b) quenched domain mode
c) LSA mode                             d) hybrid mode

1. For using as a local oscillator for frequency measurements, the most suitable microwave source would be :

a) TWT                                      b) Double cavity klystron
c) reflex klystron                        d) magnetron

1. An IMPATT diode has a drift length of 4 mm. The drift velocity of Si is 10^5m/s. The operating frequency of the IMPATT diode is:

a) 25GHz          b) 20GHz          c) 12.5 GHz       d) 125 MHz
Antenna

1. Which of the following will have least wavelength

a) VHF              b) EHF              c) HF                d) UHF

1. 30 to 300 MHz frequency is catagorized as  :

a) MF                b) VHF              c) UHF              d) SHF

1. For a frequency of 30 MHz the wavelength will be :

a) 10m              b) 1m                c) 0.1m             d) 0.01m

1. The range of audio frequency is :

a) 20kHz to 15 MHz                   b) 20 kHz to 150 MHz
c) 20 Hz to 15MHz                     d) 20 Hz to 15 kHz

1. The unit of electric field intensity E is :

a) Volts/metre                            b) Ampere/metre
c) Coulombs/metre                     d) Henry/metre

1. The current distribution on a half wave dipole is :

a) uniform          b) sinusoidal      c) triangular       d) complex

1. For a very high frequencies earth acts as a :

a)  conductor     b) dielectric       c) resistor          d) None of these

1. A wavelength of 15mm could be expected in :

a) VHF              b) HF                c) EHF              d) SHF

1. An antenna is synonymous to a :

a) generator       b) transformer    C) regulator       d) reflector

1. Free space is the :

a)       region outside the antenna region
b)       region within the antenna region
c)       region around the antenna tower
d)       None of these

1. Magnesium is alloyed with conducting materials for antenna primarily with the purpose of

a)       increasing efficiency
b)       improving radiative power
c)       reducing weight
d)       increasing density

1. The material having directional properties are known as :

a) homogenous                          b) isotropic
c) anisotropic                             d) oriental

1. A short vertical grounded antenna is required to radiate at 1 MHz. The effective height of the antenna is 30m. The calculated value of radiation resistance is :

a) 1.58W           b) 158W            c) 15.8W           d) None of these

1. If a vertical dipole antenna is used in conjunction with a loop antenna for direction finding, then the field pattern obtained will be :

a)
b)
c)
d)

1. The gain of an antenna :

a)       varies inversely as wavelength
b)       varies inversely as square of wavelength
c)       is independent of wavelength
d)       varies directly as wavelength

1. The near field of an antenna varies as :

a) 1/r² b) 1/r                 c) r                   d) 1/r⁴

1. Yagi antenna is used for :

a) television                               b) radar
c) medium wave broadcasting     d) None of these

1. A broad side array is shown in the figure below, in which the elements are placed at equal distances. The direction of maximum radiation is represented by :

a) AA’               b) BB’               c) CC’               d) DD’

1. Which of the following will increase the antenna radiation efficiency?

a)       Use of larger section of conductor
b)       providing insulation on conductor
c)       top loading of antenna
d)       any of the above

1. The effective height of an antenna is slightly greater than physical height be cause :

a)       wave velocity in antenna is less than its velocity in free space.
b)       wave velocity in antenna is more than that of free space.
c)       resistance of antenna is less than that of free space.
d)       None of the above.

1. An antenna is considered to be in free space when the height above the ground is :

a) >l                 b) >2l               c) >l /2             d) > 5l

1. If short circuited and open circuited impedances are 5 ohms and 20 ohms, then characteristic impedance is :

a) 1 ohm           b) 10 ohms        c) 25 ohms        d) 100 ohms

1. The director in a Yagi antenna :

a)       is longer than the radiating element
b)       is shorter than the radiating antenna
c)       can be longer or shorter than the radiating element
d)       does not exist.

1. An antenna receives twice as much signal power from the front as from the back. What is the front to back ratio in dB :

a) 2 dB              b) 4 dB              c) 6 dB              d) 3 dB

1. For two identical antennas A and B spaced l/4 apart as shown in the figure, it is possible to have null radiation along the array axis on the right side of B by having an excitation arrangement such that :

a)       the phase of current in antenna B lags behind that of antenna A by p/2 radians.
b)       currents in the antenna are in phase
c)       the phase of current in antenna A lags behind that of antenna B by p/2 radians
d)       current in the antennas are out of phase by p radians

1. If a current element of a very small length and carrying a current I_oe^justradiates a total average power P_r into free space, then P_r will be proportional to :

a) I_o b) I²_o c) I³_o d) I ^1-2 _o

1. A dipole antenna of l/8 length has an equivalent total loss resistance of 1.5W. The efficiency of the antenna is :

a) 0.89159%      b) 8.9159%        c) 89.159%        d) 891.59%

1. Which of the following is the radiation pattern of Rhombic antenna ;

a) A                  b) B                  c) C                  d) D

1. Which of the following is the radiation pattern of Yagi – uda antenna :

a) A                  b) B                  c) C                  d) D

1. A short dipole and a half-wave dipole have radiation resistance of 0.4W and 72W respectively. If the former requires 10A rms current for certain total output power radiated, what would be the current required (approx) by the latter for the same output?

a) 0.25 A           b) 0.50 A           c) 0.75 A           d) 1.0 A

1. Antenna used in radar is :

a) dipoles                                  b) yagi antenna
c) parabolic dishes                     d) None of these

1. Television receiver antenna is usually :

a) rhombic antenna                    b) yagi antenna
c) parabolic dishes                     d) turnstile antenna

1. Induction and radiation fields are equal at a distance equal to :

a) 6/l                b) 6l                 c) l/6                d) 6/l²

1. Which of the following antennas gives circular polarization :

a) yagi – uda                              b) parabolic
c) dipole                                    d) helical

1. The gain of a parabolic reflector antenna is given by :

a) 6(D/l)² b) 6(l/D)² c) 70 l /D          d) 140 l /D

1. If l₁, l₂, l₃, l₄ …………  are length of different elements of a log periodic antenna, then which of the following is true.

a)
b)
c)
d)

1. Which of the following statement is false?

a)       A grounded l/4 antenna is one half the length of a l/2 dipole.
b)       A vertical antenna transmits in all directions, in a circle in a horizontal plane.
c)       A grounded vertical antenna transmits ground waves and sky waves.
d)       A counter poise must be a good insulator.

1. Which of the following can make the antenna electrically longer?

a)       Series capacitor
b)       capacitive top loading
c)       vertical polarisation
d)       Circular polarsation

1. A plane electromagnetic wave travels in dielectric medium of relative permittivity 9 relatie to free space, the velocity of propagation in the dielectric is  :

a)       increased by a factor of 9
b)       increased by a factor of 3
c)       unchanged
d)       reduced by a factor of 1/3

1. A unipole is also known as :

a)       omnidirectional radiator
b)       unidirectional radiator
c)       line radiator
d)       None of the above

1. Radiation intensity does not depend upon :

a)       the antenna direction
b)       distance from the radiator
c)       both (a) and (b) above
d)       None of the above

1. The numerical value of directivity of current element and half wave dipole is respectively 1.75 dB and 2.15 dB. The directive gain of half wave dipole over current element will be :

a) 3.96 dB         b) 1.22 dB         c) 0.4 dB           d) 0.81 dB

1. In case of antenna, the ratio of the power radiated in the desired direction to the power radiated in the opposite direction is known as :

a)       transmission efficiency
b)       front to back ratio
c)       loss coefficient
d)       None of the above

1. In case of antenna decreasing Q :

a)       increases bandwidth
b)       decreases bandwidth
c)       independent of bandwidth
d)       None of the above

1. The directional pattern of loop antennas :

a)       depends on shape of antenna loc
b)       is independent of shape of the loop
c)       depends on number of turns of loop
d)       None of the above

1. The ratio of radiation intensity in a particular direction to average radiated power is called :

a)       directive gain
b)       power gain
c)       directivity
d)       DIRP

1. EIRP is defined as :

a)       Input power X Max gain
b)       Input power/Max. gain
c)       Input power + Max gain
d)       Max gain/input power

1. For large cross – sectional antennas like horn, parabolic reflector etc., if A_pis the physical aperture and A_e the effective aperture than :

a) A_e < A_p b) A_e > A_p
c) A_e = A_p d) Any of the above

1. The total field produced by an antenna array ststem at a great distance from it is :

a)       sum of the field produced by the individual antennas of the array system
b)       directional gain of antenna
c)       linear antenna gain
d)       vector sum of the field produced by the individual antennas of the array system.

1. The statements at the left are to be matched with the statements at the right :

1. Rhombic antenna       a) flat line
2. folded dipole              b) 292W radiation resistance
3. SWR of 1                  c) non resonant
4. HF band                    d) 3 to 30 MHz
which of the following represents the matching pairs :
a)       1 (a)  2 (d) 3 (c) 4 (d)
b)       1 (d) 2 (c) 3 (b) 4 9a)
c)       1 (c) 2 (b) 3 (a) 4 (d)
d)       1 (b) 2 (c) 3 (a) 4 (d)

1. The radiation pattern of Hertzian dipole in the plane perpendicular to dipole is a :

a) null                                       b) circular
c) figure of eight                         d) none of the above

1. An isotropic antenna is radiating a power of 1 watt. At a distance of 1 metre, the power per unit area will be :

a) 1 watt/m² b) 4p watt /m²
c) ¼ p watt/m² d) 2p watt/m²

1. The parabola antenna is :

a) omnidirectional                       b) non resonant
c) a figure of eight                      d) highly directional

1. The intrinsic impendance of free space :

a)       increases with increase of frequency
b)       decreases with increase of frequency
c)       does not depend on frequency
d)       behaves randomly

1. How many parasitic elements are used in a driven array?

a) 1                   b) 2                   c) 4                   d) None

1. Microwave antenna aperture efficiency depends on :

a) feed pattern                           b) antenna aperture
c) surface losses                       d) low side lobe level

1. A loop antenna is a commonly used for :

a) radar                                     b) direction finding
c) satellite communication          d) all of the above

1. The beamwidth between nulls of 140 cm parabolic reflector used at 6 GHz is :

a) 2.5 degrees                           b) 5 degrees
c) 10 degrees                            d) 7.5 degrees

1. Five isotropic element placed along the x – axis are fed by in-phase currents of equal amplitudes. The spacing between successive elements is l/4. Consider the following statements about the directivity pattern of the array :
2. The array will have a maximum in the direction of Y – axis
3. The field strength in the X – axis direction will be zero
4. The directivity pattern will have minor lobes.

Of the statements given above :
a)       1, 2 & 3 are correct
b)       1 and 2 are correct
c)       2 and  3 are correct
d)       1 and 3 are correct

1. A parabolic dish has a diameter of 10m. The maximum possible (ideal) gain of the antenna at l = 314 cm will be :

a) 18 dB            b) 40 dB            c) 50 dB            d) 60 dB

1. The electric field strength produced by an antenna varies :

a)       directly as the square root of the radiated power
b)       directly as the radiated power
c)       directly as the square of the radiated power
d)       inversely as the square root of the radiated power

1. The horn antenna is typically used at :

a) 100 kHz                                b) 100 MHz
c) 1000 MHz                              d) 100 Hz

1. The service range of a TV transmitter is largely determined by:

a)       height of the antenna
b)       gain of the antenna
c)       frequency of the transmitter
d)       Any of the above

1. The gain of a parabolic antenna increases with :

a)       increase in antenna diameter
b)       reduction in antenna diameter
c)       decrease in frequency
d)       None of the above

1. The polarization of electromagnetic wave is in :

a)       the direction of electric field
b)       the direction of magnetic field
c)       the direction of electric and magnetic fields
d)       None of the above

1. The frequency range for satellite communication is :

a)       3 to 30 kHz
b)       300 to 3000 kHz
c)       3000 to 30.000 MHz
d)       30.000 to 300.000 MHz

1. The transmission antennas for lower frequencies (below 500 kHz) are generally :

a)       vertical grounded wire type
b)       horizontal suspended wire type
c)       parabolic reflector type
d)       any of the above

1. A vertical earthed antenna is resonant when its physical height is equal to :

a) l                   b) l/2                c) l/4                d) l/8

1. In a vertical earthed antenna the base input impedance will be capacitive for a height :

a) less than l/4                          b) between l/4 and l/2
c) between l/4 and 3l/2              d) more than 3l/2

1. Capacitance hats are installed on low frequency antenna to :

a)       increase the effective length
b)       reduce the effective length
c)       protect against lightening
d)       protect against corona effects

1. An antenna is :

a)       inductive
b)       capacitive
c)       resistive above its resonant frequency
d)       None of the above

1. The parabolic and lens antennas are used extensively at :

a) SW                                       b) Medium wave
c) microwaves                            d) None

1. The bandwidth of an antenna is  :

a)       directly proportional to Q
b)       inversely proportional to Q
c)       directly proportional to Q²
d)       directly proportional to I/Q²

1. The maximum effective aperture of a microwave antenna which has a directivity of 800 will be :

a) 63.69 l² b) 633.9 l² c) 6.369 l² d) 0.639 l²

1. A thin dipole antenna is l/15 long. Its radiation resistance will be :

a) 3.5 W            b) 0.35W           c) 35W              d) 7W

1. The directivity of small current element of length l/20 s :

a) 0.05              b) 20                 c) 1.5                d) 1

1. An isotropic antenna is radiating 1 kW. The field at a distance of 1 km from it will be :

a) 173m V/m     b) 242m V/m     c) 122m V/m     d) 1m V/m

1. A transmitting antenna having an effective height of 61m takes a current of 50 Amp (rms) at a wavelength of 625 metres. The radiation resistance of the antenna is :

a) 15W              b) 7.5W             c) 30W              d) 3.75W

1. In the above question, the power radiated will be :

a) 37.5 kW        b) 18.75 kW      c) 75 kW           d) 9.3 kW

1. An antenna of input resistance 73 ohm is connected to a 50 ohm line. If losses are ignored, then its efficiency will be nearly :

a) 0.19              b) 0.81              c) 0.97              d) 1.19

1. Consider the following statements about log – periodic antennas :

a)       They operate over a wide frequency range
b)       Input impedance varies periodically with the logarithm of frequency.
c)       Logarithm of input impedance varies periodically with frequency.
d)       For single frequency operation only a portion of the antenna radiates.
Of these statements :
a)       1,2 and 4 are correct
b)       3 and 4 are correct
c)       1 and 4 are correct
d)       1 alone is correct.

1. Match List – I with List – II and select the correct answer using the codes given below the lists :

List – I                           List – II
A. End fire array 1. inefficient radiation
B. Half wave dipole         2. in -phase excitation
C. Broadside array         3. quadrature excitation
D. Hertzian                    4. broadcast antenna
Codes :
A          B          C          D
a)         3          2          4          1
b)         3          4          2          1
c)         1          4          2          3
d)         1          2          4          3

1. Helical antenna are often used for satellite tracking at VHF because of :

a)       super refraction
b)       troposcatter
c)       ionospheric refraction
d)       the Faraday effect

1. Side lobe of an antenna causes :

a)       Reduction in gain of antenna
b)       reduces beam width of antenna
c)       ambiguity in direction finding
d)       All of the above

1. Large antenna is used in radar because :

a)       it gives higher gain
b)       it gives less side lobes
c)       increase the beamwidth
d)       None of the above

1. Antenna commonly used for microwave links are

a)       Yagi – uda antenna
b)       log periodic antenna
c)       paraboloidal dishes
d)       rhombic antenna

1. A hertzian dipole has a radiation pattern with :

a)       a null in the direction of the dipole
b)       a null in the plane perpendicular to the dipole
c)       a peak in the direction of the dipole
d)       none of the above

1. A rhombic antenna is a :

a)       resonant antenna
b)       omnidirectional antenna
c)       non – resonant antenna
d)       None of the above

1. Cassegrain feed is used with a parabolic reflecter 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

1. Multiple wire conductors are used for Rhombic antenna to ;

a)       increase strength
b)       reduce capacitance
c)       reduce characteristic impedance
d)       All of the above

1. A helical antenna is used for satellite tracing because of its :

a)       Circular polarisation
b)       manevarability
c)       broad bandwidth
d)       good front to back ratio

1. To produce given radiation attern, a Marconi antenna need be:

a)       double the size of the hertz antenna
b)       half the size of the Hertz antenna
c)       of some size as he Hertz antenna
d)       four times the size of the Hertz antenna

1. Antenna arrays are used :

a)       to obtain a desired radiation pattern
b)       to obtain an increased radiation efficiency
c)       to increase the effective length of the antenna
d)       to reduce the side lobes.

1. An antenna has an effective height of 50m and the current at the base is 450 Amp (rms) at 40 kHz. The power radiated is :

a) 14 kW           b) 28 kW           c) 42 kW           d) 56 kW

1. At what distance from a 100 Hz circuit is the radiation field approximately equal to the induction field :

a) 477 km          b) 954 km          c) 18000 km      d) 238 km

1. A linear broadside array consists of four equal isotropic in phase point source with l/3 spacing (overall length of the array -= l). The half power beamwidth is :

a) 51°                b) 115°              c) 25.6°             d) 102°

1. A thin dipole antenna l/15 long has a beam solid angle given by :

a) 8 d_r b) 16 d_r c) 24 d_r d) 32 d_r

1. The beamwidth between first nulls of a 2m paraboloid reflector operating at 6 GHz is :

a) 1.9°               b) 3.8°               c) 5.7°               d) 7.6°

1. Cassegrain feed :

a)       eliminates aperture blocking
b)       increases the gain of the paraboloid reflector
c)       reduces the long runs of transmission line to primary feed
d)       reduces the power in the side lobes.

1. The problem of aperture blocking in a cassegrain feed can be eliminated by using :

a)       offset reflector
b)       trans – reflector
c)       rear feed
d)       dipole feed

1. The required phase difference between the feeds of successive elements in an end fire array :

a)       is zero
b)       is 180 degrees
c)       depends upon the distance between the elements
d)       depends upon the number of elements

1. Increase in the number of radiators in a large – sized broadside array with fixed inter-element spacing leads to :

a)       increased side lobes
b)       widening of the main lobes
c)       narrowing of the main lobes
d)       None of the above

1. A linear end – fire array of isotropic elements has :

a)       maximum radiation along the           of the array
b)       maximum radiation normal to   line of the array
c)       maximum radiation in a direction which depends on the length of the array
d)       is isotropic

1. The actual gain if a parabolic antenna diameter D = 10 can be approximated by G = 2p (D/l)² what is the effective aperture area of the antenna?

a) 100m² b) 75 m² c) 50m² d) 25m²

1. One of the following is a of non – resonant antenna

a)       the rhombic antenna
b)       the folded dipole
c)       the end fire – array
d)       the broadside array

1. One of the following is very useful as multiband HF receiving antenna. This is the :

a)       conical horn
b)       folded dipole
c)       log – periodic
d)       square loop

1. Which of the following antennas is best excited from a waveguide ?

a) biconical        b) horn              c) helical           d) discone

1. Which one of the following term is in-correct for Yagi – Uda array?

a)       good bandwidth
b)       parasitic elements
c)       folded dipole
d)       high gain

1. The standard reference antenna for the directive gain is the :

a)       infinitesimal dipole
b)       isotropic antenna
c)       elementary doublet
d)       half wave dipole

1. Top loading is sometimes used with an antenna in order to increase its :

a)       effective height
b)       bandwidth
c)       beamwidth
d)       input capacitance

1. In end fire array the principle direction of radiation :

a)       is perpendicular to the array axis
b)       is perpendicular to the array axis and also to the plane containing the array elements
c)       same as the direction of the array axis
d)       is at 45° to the direction of array axis

1. In binomial arrays the elimination of secondary lobes takes place :

a)       at the cost of directivity
b)       at the cost of gain
c)       at the cost of beamwidth
d)       All of the above

1. In a broadside array of 20 isotropic radiators, equally spaced at a distance of  l/2, the beamwidth between first nulls is :

a) 51.3 degrees                          b) 11.46 degrees
c) 22.9 degrees                          d) 102.6 degrees

1. In a broadside array maximum radiation occurs :

a)       at 90° to the line of the array
b)       at 45° to the line of the array
c)       along the line of the array
d)       at 60° to line of the array

1. Radiation resistance of a Hertzian dipole of length dl is :

a)       80p (dl/l)² ohms
b)       80p (dl /l) ohms
c)       80 (ldl/p) ohms
d)       80 (pdl / l)² ohms

1. In a turnstile antenna, the crossed dipoles are excited with voltage such that the phase shift between the voltage is :

a) zero              b) 45°                c) 90°                d) 180°

1. A helical antenna is used for satellite tracking because of its :

a)       circular polarisation
b)       maneuverability
c)       broad bandwidth
d)       good front to back ratio

1. The discone antenna is :

a)       a useful direction – finding antenna
b)       used as a radar receiving antenna
c)       circularly polarized like other circular antennas
d)       useful as a UHF receiving antenna

1. One of the following is not an omnidirectional antenna :

a)       half wave dipole
b)       log – periodic
c)       discone
d)       marconi

1. Microwave antenna aperture efficiency depends on :

a)       feed pattern
b)       antenna aperture
c)       surface losses
d)       low side lobe level

1. The direction of radiation in the collinear array shown below will be :

a) AA’               b) BB’               c) CC’               d) DD’

1. The differential loop signal voltage in aloop antenna depends upon :

a)       the wavelenth of incoming signal
b)       the angle of loop orientation
c)       the loop area
d)       all of these

1. Match List I with List II and select the correct answer using the codes given below the lists :

A. Cassegrain antenna               1. Large bandwidth
B. Yagi antenna                         2. Direction finding
C. Parabolic reflector                  3. Radar antenna
D. Loop antenna                        4. Directional transmission
Codes :
A          B          C          D
a)         1          4          2          3
b)         3          1          4          2
c)         2          4          3          1
d)         3          2          4          1

1. Polarisation of radio waves is determined by :

a)       the directivity of the antenna
b)       the direction of the magnetic flux lines with respect to the surface of earth
c)       the direction of electric flux lines with respect to the surface of the earth
d)       the efficiency of the antenna.

1. An antenna is to cover the VHF freq., range from 54 to 216 MHz. If the radiated is required to be 25W for an input current of 0.5 A the effective length of antenna will be

a) 0.988 m         b) 0.629 m         c) 0.4943m        d)n 0.5 m

1. Which of the following is the correct angular aperture for a paraboloidal reflector antenna for which the aperture number is 0.25?

a) 45°                b) 90°                c) 120°              d) 180°

1. Match List I with List II and select the correct answer using the codes given below the lists :

List I (types of antenna)              List II (Features)
A. Helical antenna                      1. circular polarization
B. Horn antenna             2. simplicity and
compactness
C. Hoghorn antenna                   3. low noise
D. Parabolic dish with                 4. high
horn feed.                            directivity
Codes :
A          B          C          D
a)         1          2          3          4
b)         4          3          2          1
c)         2          1          4          3
d)         1          2          4          3

1. T.V. broadcasting in India is done in :

a) VHF bands                            b) UHF bands
c) microwave bands                    d) HF bands

1. A radio station works at 800 kHz and uses AM. If this is a public broadcast system, it should transmit using :

a)       parabolic reflector to transmit all round
b)       turnstile antenna for the required band
c)       half – wave long horizontal wire
d)       a vertical antenna less than quarter for practical reasons.

1. 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°                   d) None of these

1. The absorption of electromagnetic waves by the atmosphere depends on :

a)       the frequency in use
b)       the polarization of waves
c)       distance from the transmitter
d)       all of the above

1. Two dissimilar antennas having their maximum directivites equal :

a)       must have their beamwidths also equal
b)       cannot have their beamwidths equal because they are dissimilar antennas
c)       may not necessarily have their maximum power gains equal
d)       must have their effective aperture areas (capture areas) also equal.

1. While determining antenna height for terrestial microwaves links, the effect of refraction from the atmosphere is taken care of by considering the effective curvature of the earth to be :

a)       2/3 times the radius of earth
b)       ¾ times the radius of earth
c)       4/3 times the radius of earth
d)       3/2 times the radius of earth

1. Match List I (Microwave band) with List II (frequency used in satellite communication) and select the correct answer using codes given below the correct answer using codes given below the list :

List I                             List II
A. C – band                    1. 12GHz to 14 GHz
B. Ku – band                  2. 24 GHz to 26 GHz
C. Ka – band                  3. 20 GHz to 30 GHz
4. 4GHz to 6 GHz
Codes :
A          B          C
a)         4          2          1
b)         2          1          3
c)         4          1          3
d)         3          4          2

1. A 1 km long microwave link uses two antennas each having 30dB gain. If the power transmitted by one antenna is 1W at 3HGz, the power received by the other antenna is approximately :

a) 98.6 m/W       b) 76.8 mW        c) 63.4 mW        d) 55.2 mW

1. The advantage of microwave over lower frequency signals is :

a)       increased bandwidth
b)       ability to use high gain
c)       increased secrecy
d)       all of the above

1. When the peak power is 100.000 watts and the average power is 800 watts then the duty cycle is

a) 0.008 percent             b) 0.08 percent
c) 0.8 percent                            d) 8 percent

1. For frequencies upto 1650 kHz, the transmitting antenna used is a :

a)       parabolic dish
b)       vertical antenna
c)       yagi antenna
d)       turnstile antenna

1. The wave radiated by a helical antenna is :

a)       linearly polarized
b)       right circularly polarized
c)       left circularly polarized
d)       elliptically polarized

1. The half power beamwidths (HPBW) of an antenna in the two orthogonal planes are 100 and 60 respectively. The directivity of the antenna is approximately equal to :

a) 2 dB              b) 5 dB              c) 8 dB              d) 12 dB