Antennas And Microwave Engineering Set 4

Electrical Engineering

Practice Mode Previous Next
On This Page

This set of Antennas and Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on Antennas And Microwave Engineering Set 4

Q1 | Antennas are bidirectional devices.
  • true
  • false
Answer: true
Explaination:
antennas can be used both as transmitters and receivers. as transmitters they radiate energy to free space and as receivers they receive signal from free space. hence, they are called bidirectional devices as they are used at both transmitting end and receiving end.
Q2 | Dipole antennas are an example for:
  • wire antennas
  • aperture antennas
  • array antennas
  • none of the mentioned
Answer: wire antennas
Explaination:
dipoles, monopoles, oops, yagi-uda arrays are all examples for wire
Q3 |                    antennas consist of a regular arrangement of antenna elements with a feed network
  • aperture antennas
  • array antennas
  • printed antennas
  • wire antennas
Answer: array antennas
Explaination:
array antennas consist of a regular arrangement of antenna elements with
Q4 | Antennas having a constant pattern in the azimuthal plane are called                            
  • high gain antenna
  • omni directional antenna
  • unidirectional antenna
  • low gain antenna
Answer: omni directional antenna
Explaination:
omni directional antennas radiate em waves in all direction. if the
Q5 | If the power input to an antenna is 100 mW and if the radiated power is measured to be 90 mW, then the efficiency of the antenna is:
  • 75 %
  • 80 %
  • 90 %
  • insufficient data
Answer: 90 %
Explaination:
antenna efficiency is defined as the ratio of radiated power to the input power to the antenna. substituting the given
Q6 | Which of the following is false regarding Antenna array?
  • directivity increases
  • directivity decreases
  • beam width decreases
  • gain increases
Answer: directivity decreases
Explaination:
a single antenna provides low gain and less directivity. to increase the directivity antenna arrays are used. with the antenna arrays, directivity and gain increases and beam width decreases.
Q7 | Electrical size of antenna is increased by which of the following?
  • antenna array
  • decreasing the coverage area
  • increasing the coverage area
  • using a single antenna
Answer: antenna array
Explaination:
to increase the directivity antenna arrays are used. with the antenna arrays, directivity and gain increases and beam width decreases. the electrical size of the antenna is increased by placing an array antenna together to achieve high directivity.
Q8 | For long distance communication, which of the property is mainly necessary for the antenna?
  • high directivity
  • low directivity
  • low gain
  • broad beam width
Answer: high directivity
Explaination:
long distance communication requires antenna with high directivity. to increase the directivity antenna arrays are used. with the antenna arrays, directivity and gain increases and beam width decreases.
Q9 | Which of the following is false about the single antenna for long distance communication?
  • enlarging may create side lobes
  • no side lobes
  • high directivity is required
  • high gain is required
Answer: no side lobes
Explaination:
high directive antennas are required for the long distance communications. the array of antennas is used to increase the directivity. the directivity can be increased by increasing the dimensions of antenna but it creates side lobes.
Q10 | The electrical size of antenna is increased by antenna array to avoid size lobes compared to single antenna.
  • true
  • false
Answer: true
Explaination:
increasing the dimensions of antennas may lead to the appearance of the side lobes. so by placing a group of antennas together the electrical size of antenna can be increased. with the antenna arrays, directivity and gain increases and beam width decreases.
Q11 | Total resultant field obtained by the antenna array is given by which of following?
  • vector superposition of individual field from the element
  • maximum field from individual sources in the array
  • minimum field from individual sources in the array
  • field from the individual source
Answer: vector superposition of individual field from the element
Explaination:
the total resultant field is obtained by adding all the fields obtained by the individual sources in the array. an array containing n elements has the resultant field equal to the vector superposition of individual field from the elements.
Q12 | If the progressive shift in antenna array is equal to zero then it is called                    
  • broad side
  • end-fire
  • yagi-uda
  • fishbone antenna
Answer: broad side
Explaination:
the total phase difference of the fields is given by Ѱ=kdcosθ+β
Q13 | What is the progressive phase shift of the end-fire array?
  • 0
  • 90 c) 180
  • d) 60
Answer: d) 60
Explaination:
the progressive phase shift of the end-fire array is 180°. it is a linear array whose direction of radiation is along the axis of the array. for a broadside array it is 0°.
Q14 | Which of the following statement about antenna array is false?
  • field pattern is the product of individual elements in array
  • field pattern is the sum of individual elements in array
  • resultant field is the vector superposition of the fields from individual elements in array
  • high directivity can be achieved for long distance communications
Answer: field pattern is the sum of individual elements in array
Explaination:
the total resultant field is obtained by adding all the fields obtained by the individual sources in the array. radiation pattern is obtained by multiplying the individual pattern of the element. field pattern is the product of individual elements in array. antenna arrays are used to get high directivity with less side lobes.
Q15 |                                are used in the final stages of radar and radio transmitters to increase the radiated power level.
  • power amplifiers
  • oscillators
  • transistors
  • attenuators
Answer: power amplifiers
Explaination:
power amplifiers are used in the final stages of radar and radio transmitters to increase the radiated power level. output of power amplifiers are in the range of 100- 500 mw.
Q16 | Important factors to be considered for power amplifier design are:
  • efficiency
  • gain
  • thermal effect
  • all of the mentioned
Answer: all of the mentioned
Explaination:
as per the application requirement and considering various aspects of an amplifier like efficiency, gain, thermal efficiency and inter modulation distortion, amplifiers need to be designed.
Q17 | 1 MICROWAVE PASSIVE COMPONENTS: DIRECTIONAL COUPLER, POWER DIVIDER, MAGIC TEE ATTENUATOR, RESONATOR
  • true
  • false
Answer: true
Explaination:
power amplifier is the primary consumer of dc power in most hand-held wireless devices, so amplifier efficiency is an important consideration. amplifier efficiency is the ratio of rf output power to dc input power.
Q18 | Gain of power amplifiers                      with increase in operating frequency.
  • increases
  • decreases
  • increases exponentially
  • decreases exponentially
Answer: decreases
Explaination:
silicon bipolar junction transistor amplifiers in the cellular telephone band of 800-900 mhz band have power added efficiencies of about 80%. but this efficiency drops quickly with increase in the operating frequency.
Q19 |                        amplifiers are linear circuits, where the transistor is biased to conduct over the entire range of the input signal cycle.
  • class a amplifiers
  • class b amplifiers
  • class c amplifiers
  • none of the mentioned
Answer: class a amplifiers
Explaination:
class a amplifiers are linear circuits, where the transistor is biased to conduct over the entire range of the input signal cycle. because of this, class a amplifiers theoretically have a maximum efficiency of 50%.
Q20 | A class B amplifier consists of                 transistors in order to conduct the input signal over the entire cycle.
  • 1
  • 2
  • 4
  • 6
Answer: 2
Explaination:
class b amplifier is biased to conduct only during one-half of the input signal cycle. 2 complementary transistors are operated in a class b push pull amplifier to provide amplification over the entire cycle.
Q21 | Power amplifiers in the increasing order of efficiency is:
  • class a, b, c
  • class c, a, b
  • class b, a, c
  • efficiency of all the 3 amplifiers is the same
Answer: class a, b, c
Explaination:
class a amplifiers have an efficiency of about 50%. class b amplifiers have an efficiency of about 78%, class c amplifiers can achieve efficiencies up to 100%. in the increasing order of efficiency, c
Q22 | Behavior of a transistor in power amplifiers is unpredictable at all input signal levels.
  • true
  • false
Answer: false
Explaination:
a transistor behaves linearly for signal powers below 1db compression point and so, the small –signal scattering parameters should not depend either on the input power level or the output termination impedance.
Q23 | If the output power of an amplifier is 10 V, and the input power supplied to the amplifier is 0.229 V given that the DC voltage used is
  • 25%
  • 50%
  • 75%
  • 35%
Answer: 25%
Explaination:
efficiency of a power amplifier is (pout- pin)/ pdc substituting the given values in the above expression, efficiency of the power amplifier is 25%.
Q24 | If a power amplifier has an output power of 10 W, and an amplifier gain of 16.4 dB, then the input drive power is:
  • 400 mw
  • 225 mw
  • 229 mw
  • 240 mw
Answer: 229 mw
Explaination:
input drive power required to get an output of 10 w is pout (dbm)- g (db). g is the gain of the amplifier. substituting the given values in the above equation, 229 mw.
Q25 | GaAs is used in the fabrication of GUNN diodes because:
  • gaas is cost effective
  • it less temperature sensitive
  • it has low conduction band electrons
  • less forbidden energy gap
Answer: less forbidden energy gap
Explaination:
in gaas, the conduction band lies directly above the top of the valence band. the lowest energy conduction band in gaas is called as primary valley. gaas consists of six secondary valleys. the bottom of one of the secondary valley is at an energy difference of 0.35 ev with the bottom of the primary valley in conduction band.
Previous Next