170+ Antennas and Microwave Engineering Solved MCQs

1.

The major drawback of frequency multipliers is that they have:

A. higher attenuation
B. complex construction methods
C. complex design
D. none of the mentioned
Answer» C. complex design
Explanation: designing a good quality frequency multiplier is more difficult since it non-linear analysis, matching at multiple frequencies, stability analysis and thermal considerations. considering all these issues for designing a multiplier makes it very complex.
2.

Oscillators operating at millimeter wavelength are difficult to realize and are also less efficient.

A. true
B. false
Answer» A. true
Explanation: as frequency increases to the millimeter wave range, it becomes increasingly difficult to build fundamental frequency oscillators with good power, stability and noise characteristics. an alternative approach is to produce a harmonic of a low frequency oscillator through the use of frequency multiplier.
3.

A major disadvantage of frequency multipliers is that they multiply the noise factor along with frequency.

A. true
B. false
Answer» A. true
Explanation: a disadvantage of frequency multipliers is that noise levels are also increased by the multiplication factor.
4.

If a frequency multiplier has a multiplication factor of 10, then the increase in noise level due to frequency multiplication is:

A. 10 db
B. 20 db
C. 25 db
D. 15 db
Answer» B. 20 db
Explanation: for a frequency multiplier, the increase in noise power is given by 20 log n, where n is the multiplication factor of the multiplier. substituting in the below equation, increase in noise level is 20 db.
5.

In a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with                   at all frequencies other than required harmonic.

A. real impedances
B. reactive impedance
C. complex impedance
D. none of the mentioned
Answer» B. reactive impedance
Explanation: in a diode frequency multiplier, an input signal of frequency fo applied to the diode is terminated with reactive impedance at all frequencies other than required harmonic nfo. if the diode junction capacitance has a square –law i-v characteristic , it is necessary to terminate unwanted harmonics with short circuit.
6.

Resistive multipliers are more efficient as compared to reactive multipliers.

A. true
B. false
Answer» B. false
Explanation: resistive multipliers generally use forward biased schottky-barrier diodes to provide non linear characteristic. resistive multipliers have low efficiency but have better bandwidth.
7.

Reactive multipliers have a disadvantage that they cannot be used at very high frequencies and they become less efficient.

A. true
B. false
Answer» A. true
Explanation: at millimeter frequencies, varactor diode exhibits resistive property. hence, at high frequency the multiplier becomes lossy and also does not offer high bandwidth, which is a major disadvantage.
8.

For a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is:

A. 50 %
B. 25 %
C. 75 %
D. 12.5 %
Answer» B. 25 %
Explanation: for a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is given by 1/m2 where m is the multiplication factor. for a factor 2 multiplier, maximum theoretical conversion efficiency is 25 %.
9.

                   is a device that converts electrons to photons or vice-versa.

A. antenna
B. electron gun
C. photon amplifier
D. microwave tube
Answer» A. antenna
Explanation: antenna is a device that converts electrons into photons or vice versa. a transmitting antenna converts electrons into photons while a receiving antenna converts photons into electrons.
10.

The basic equation of radiation that is applied to any antenna irrespective of the type of the antenna is:

A. il= qv
B. iq = lv
C. i/l=q/v
D. none of the mentioned
Answer» A. il= qv
Explanation: basic equation of radiation is given by il=qv. i is the time change in current, l is the length of the current element, q is the charge v is the acceleration of the charge.
11.

The number of patterns radiation pattern required to specify the characteristic are :

A. three
B. four
C. two
D. five
Answer» A. three
Explanation: the three patterns required are, θ component of the electric field as the function of the angles as θ and φ, the φ component of the electric field as the function of the angles θ and φ, the phase of these fields as a functions of the angle φ and θ .
12.

The beam width of the antenna pattern measured at half power points is called:

A. half power beam width
B. full null beam width
C. beam width
D. none of the mentioned
Answer» A. half power beam width
Explanation: the beam width of an antenna measure at half of the maximum power received by an antenna or the 3 db beam width of the antenna is termed as half null beam width.
13.

An antenna has a field pattern E (θ) =cos θ. cos 2θ. The first null beam width of the antenna is:

A. 450
B. 900
C. 1800
D. 1200
Answer» B. 900
Explanation: half power beam width of the antenna is obtained by equating the field pattern of the antenna to 0.707 (half power point) and finding θ. 2θ gives the value of beam width. twice the half power beam width gives the first null beam width. with the same steps applied, the half power beam width of the antenna is 450. first null beam width is 900.
14.

The solid area through which all the power radiated by the antenna is:

A. beam area
B. effective area
C. aperture area
D. beam efficiency
Answer» A. beam area
Explanation: the beam area is the solid angle through which all of the power radiated by the antenna would stream if p (θ, φ) maintained its maximum value over beam area and zero elsewhere. this value is approximately equal to the angles subtended by the half power points of the main lobe in the two principal planes.
15.

A                      is a device that converts a guided electromagnetic wave on a transmission line into a plane wave propagating in free space.

A. transmitting antenna
B. receiving antenna
C. radar
D. mixer
Answer» A. transmitting antenna
Explanation: a transmitting antenna is a device that converts a guided electromagnetic wave on a transmission line into a plane wave propagating in free space. it appears as an electrical circuit on one side, provides an interface with a propagating plane wave.
16.

Dipole antennas are an example for:

A. wire antennas
B. aperture antennas
C. array antennas
D. none of the mentioned
Answer» A. wire antennas
Explanation: dipoles, monopoles, oops, yagi-uda arrays are all examples for wire antennas. these antennas have low gains, and are mostly used at lower frequencies.
17.

                   antennas consist of a regular arrangement of antenna elements with a feed network

A. aperture antennas
B. array antennas
C. printed antennas
D. wire antennas
Answer» B. array antennas
Explanation: array antennas consist of a regular arrangement of antenna elements with a feed network. pattern characteristics such as beam pointing angle and side lobe levels can be controlled by adjusting the amplitude and phase excitation of array elements.
18.

A parabolic reflector used for reception with the direct broadcast system is 18 inches in diameter and operates at 12.4 GHz. The far-field distance for this antenna is:

A. 18 m
B. 13 m
C. 16.4 m
D. 17.3 m
Answer» D. 17.3 m
Explanation: far field distance for a reflector antenna is given by 2d2/λ. d is the diameter and λ is the operating signal wavelength.
19.

                   of an antenna is a plot of the magnitude of the far field strength versus position around the antenna.

A. radiation pattern
B. directivity
C. beam width
D. none of the mentioned
Answer» A. radiation pattern
Explanation: radiation pattern of an antenna is a plot of the magnitude of the far field strength versus position around the antenna. this plot gives the detail regarding the region where most of the energy of antenna is radiated, side lobes and beam width of an antenna.
20.

Antennas having a constant pattern in the azimuthal plane are called                            

A. high gain antenna
B. omni directional antenna
C. unidirectional antenna
D. low gain antenna
Answer» B. omni directional antenna
Explanation: omni directional antennas radiate em waves in all direction. if the radiation pattern for this type of antenna is plotted, the pattern is a constant signifying that the radiated power is constant measured at any point around the antenna.
21.

Beamwidth and directivity are both measures of the focusing ability of an antenna.

A. true
B. false
Answer» A. true
Explanation: beamwidth and directivity are both measures of the focusing ability of an antenna. an antenna with a narrow main beam will have high directivity, while a pattern with low beam will have low directivity.
22.

If the beam width of an antenna in two orthogonal planes are 300 and 600. Then the directivity of the antenna is:

A. 24
B. 18
C. 36
D. 12
Answer» B. 18
Explanation: given the beam width of the antenna in 2 planes, the directivity is given by 32400/θ*∅, where θ,∅ are the beam widths in the two orthogonal planes. substituting in the equation, directivity of the antenna is 18.
23.

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:

A. 75 %
B. 80 %
C. 90 %
D. insufficient data
Answer» C. 90 %
Explanation: antenna efficiency is defined as the ratio of radiated power to the input power to the antenna. substituting the given data in the efficiency equation, the efficiency of the antenna is 90%.
24.

If an antenna has a directivity of 16 and radiation efficiency of 0.9, then the gain of the antenna is:

A. 16.2
B. 14.8
C. 12.5
D. 19.3
Answer» A. 16.2
Explanation: gain of an antenna is given by the product of radiation efficiency of the antenna and the directivity of the antenna.
25.

Gain of an antenna is always greater than the directivity of the antenna.

A. true
B. false
Answer» B. false
Explanation: gain of an antenna is always smaller than the directivity of an antenna. gain is given by the product of directivity and radiation efficiency. radiation efficiency can never be greater than one. so gain is always less than or equal to directivity.
26.

A rectangular horn antenna has an aperture area of 3λ × 2λ. Then the maximum directivity that can be achieved by this rectangular horn antenna is:

A. 24 db
B. 4 db
C. 19 db
D. insufficient data
Answer» C. 19 db
Explanation: given the aperture dimensions of an antenna, the maximum directivity that can be achieved is 4π a/λ2, where a is the aperture area and λ is the operating wavelength. substituting the given values in the above equation, the maximum directivity achieved is 19 db.
27.

A rectangular horn antenna has an aperture area of 3λ × 2λ. If the aperture efficiency of an antenna is 90%, then the directivity of the antenna is:

A. 19 db
B. 17.1 db
C. 13 db
D. 21.1 db
Answer» B. 17.1 db
Explanation: given the aperture dimensions of an antenna, the directivity that can be achieved is ap4π a/λ2, where a is the aperture area and λ is the operating
28.

A resistor is operated at a temperature of 300 K, with a system bandwidth of 1 MHz then the noise power produced by the resistor is:

A. 3.13×10-23 watts
B. 4.14×10-15 watts
C. 6.14×10-15 watts
D. none of the mentioned
Answer» B. 4.14×10-15 watts
Explanation: for a resistor noise power produced is given by ktb, where t is the system temperature and b is the bandwidth. substituting in the above expression, the noise power produced is 4.14×10-15 watts.
29.

With an increase in operating frequency, the background noise temperature:

A. increases
B. decreases
C. remains constant
D. remains unaffected
Answer» A. increases
Explanation: the plot of frequency v/s background noise temperature shows that with the increase of the signal frequency, the
30.

The noise temperature of an antenna is given by the expression:

A. radtb + (1-rad) tp
B. (1-rad) tp
C. radtb
D. none of the mentioned
Answer» A. radtb + (1-rad) tp
Explanation: the noise temperature of an antenna is given by the expression radtb + (1-rad) tp. here, tb is the brightness temperature and tp is the physical
31.

Low is the G/T ratio of an antenna, higher is its efficiency.

A. true
B. false
Answer» B. false
Explanation: in the g/t ratio of an antenna, g is the gain of an antenna and t is the antenna noise temperature. higher the g/t ratio of an antenna better is the performance of the antenna.
32.

                   has a constant power spectral density.

A. white noise
B. gaussian noise
C. thermal noise
D. shot noise
Answer» A. white noise
Explanation: thermal noise has a power spectral density for a wide range of frequencies. its plot of frequency v/s noise power is a straight line parallel to y axis.
33.

Slotted line is a transmission line configuration that allows the sampling of:

A. electric field amplitude of a standing wave on a terminated line
B. magnetic field amplitude of a standing wave on a terminated line
C. voltage used for excitation
D. current that is generated by the source
Answer» A. electric field amplitude of a standing wave on a terminated line
Explanation: slotted line allows the sampling of the electric field amplitude of a standing wave on a terminated line. with this device, swr and the distance of the first voltage minimum from the load can be measured, from this data, load impedance can be found.
34.

If the standing wave ratio for a transmission line is 1.4, then the reflection coefficient for the line is:

A. 0.16667
B. 1.6667
C. 0.01667
D. 0.96
Answer» A. 0.16667
Explanation: ┌= (swr-1)/ (swr+1). substituting for swr in the above equation for reflection co-efficient, given swr is 1.4, reflection co-efficient is 0.16667.
35.

If the reflection coefficient of a transmission line is 0.4, then the standing wave ratio is:

A. 1.3333
B. 2.3333
C. 0.4
D. 0.6
Answer» B. 2.3333
Explanation: swr= (1+┌)/ (1-┌). where ┌ is the reflection co-efficient. substituting for the reflection co-efficient in the equation, swr is 2.3333.
36.

In the expression for phase of the reflection coefficient, Lmin stands for :

A. distance between load and first voltage minimum
B. distance between load and first voltage maximum
C. distance between consecutive minimas
D. distance between a minima and immediate maxima
Answer» A. distance between load and first voltage minimum
Explanation: lmin is defined as the distance between the terminating load of a transmission line and the first voltage minimum that occurs in the transmission line due to reflection of waves from the load end due to mismatched termination.
37.

If the normalized load impedance of a transmission line is 2, then the reflection co- efficient is:

A. 0.33334
B. 1.33334
C. 0
D. 1
Answer» A. 0.33334
Explanation: zl=z0 (1+┌)/ (1-┌), this is the expression for load impedance. normalized load impedance is the ratio of load impedance to the characteristic impedance, taking zll/z0 as 2, the reflection co-efficient is equal to 0.33334.
38.

Link budget consists of calculation of

A. useful signal power
B. interfering noise power
C. useful signal & interfering noise power
D. none of the mentioned
Answer» C. useful signal & interfering noise power
Explanation: the link analysis and its output, the link budget consists of calculations and tabulations of useful signal power and interfering noise power at the receiver.
39.

Which is the primary cost for degradation of error performance?

A. loss in signal to noise ratio
B. signal distortion
C. signal distortion & loss in signal to noise ratio
D. none of the mentioned
Answer» C. signal distortion & loss in signal to noise ratio
Explanation: there are two primary causes for the degradation of error performance.
40.

Which factor adds phase noise to the signal?

A. jitter
B. phase fluctuations
C. jitter & phase fluctuations
D. none of the mentioned
Answer» C. jitter & phase fluctuations
Explanation: when a local oscillator is used in signal mixing, phase fluctuations and jitter adds phase noise to the signal.
41.

Antennas are used

A. as transducer
B. to focus
C. as transducer & to focus
D. none of the mentioned
Answer» C. as transducer & to focus
Explanation: antennas are used as transducer that converts electronic signals to electromagnetic fields and vice versa. they are also used to focus the electromagnetic energy in the desired direction.
42.

Mechanism contributing to a reduction in efficiency is called as

A. amplitude tapering
B. blockage
C. edge diffraction
D. all of the mentioned
Answer» D. all of the mentioned
Explanation: mechanism contributing to a reduction in efficiency is called as amplitude tapering, spillover, edge diffraction, blockage, scattering, re-radiation and dissipative loss.
43.

Space loss occurs due to a decrease in

A. electric field strength
B. efficiency
C. phase
D. signal power
Answer» A. electric field strength
Explanation: due to the decrease in electric field strength there will be a decrease in signal strength as a function of distance. this is called as space loss.
44.

Antenna’s efficiency is given by the ratio of

A. effective aperture to physical aperture
B. physical aperture to effective aperture
C. signal power to noise power
D. losses
Answer» A. effective aperture to physical aperture
Explanation: the larger the antenna aperture the larger is the resulting signal power density in the desired direction. the ratio of effective aperture to physical aperture is the antenna’s efficiency.
45.

Effective radiated power of an isotropic radiator can be given as a product of

A. radiated power and received power
B. effective area and physical area
C. transmitted power and transmitting gain
D. receiving power and receiving gain
Answer» C. transmitted power and transmitting gain
Explanation: an effective radiated power
46.

A dipole antenna is also called as?

A. marconi antenna
B. yagi antenna
C. bidirectional antenna
D. hertz antenna
Answer» D. hertz antenna
Explanation: one of the most widely used antenna types is the half-wave dipole antenna. this antenna is also formally known as the hertz antenna after heinrich hertz, who first demonstrated the existence of electromagnetic waves.
47.

The impedance at the center of the antenna is known as?

A. characteristic impedance
B. radiation resistance
C. transmission impedance
D. recovery resistance
Answer» B. radiation resistance
Explanation: the transmission line is connected at the center. the dipole has an impedance of 73 v at its center, which is the radiation resistance. at the resonant frequency, the antenna appears to be a pure resistance of 73 v.
48.

What happens when the radiation resistance of the antenna matches the characteristic impedance of the transmission line?

A. no transmission occurs
B. no reception occurs
C. swr is maximum
D. swr is minimum
Answer» D. swr is minimum
Explanation: when the radiation resistance of the antenna matches the characteristic impedance of the transmission line, the swr is minimum and maximum power reaches the antenna. this allows maximum power to be transmitted.
49.

The type of dipole antenna that has a higher band width is called as?

A. conical antenna
B. yagi antenna
C. helical antenna
D. marconi antenna
Answer» A. conical antenna
Explanation: a common way to increase bandwidth in the antenna is to use a version of the dipole antenna known as the conical antenna. the overall length of the antenna is 0.73λ or 0.73(984)/f = 718.32/f. this is longer than the traditional one-half wavelength of a dipole antenna, but the physical shape changes the necessary dimensions for resonance.
50.

The radiation pattern of a half-wave dipole has the shape of a              

A. doughnut
B. sphere
C. hemisphere
D. circular
Answer» A. doughnut
Explanation: the radiation pattern of any antenna is the shape of the electromagnetic energy radiated from or received by that antenna. typically that radiation is concentrated in a pattern that has a recognizable geometric shape. the radiation pattern of a half-wave dipole has the shape of a doughnut.
51.

What is the beam width for a half wave dipole antenna?

A. 90°
B. 180°
C. 50°
D. 250°
Answer» A. 90°
Explanation: the beam width is measured between the points on the radiation curve that are 3 db down from the maximum amplitude of the curve. the maximum amplitude of the pattern occurs at 0° and 180°. the 3-db down points are 70.7 percent of the maximum. the angle formed with two lines extending from the center of the curve to these 3-db points is the beam width. the beam width is 90°. the smaller the beam width angle, the more directional the antenna.
52.

What does the beam width of an antenna tell us?

A. signal strength
B. signal power
C. directivity
D. degradation
Answer» C. directivity
Explanation: the measure of an antenna’s directivity is beam width, the angle of the radiation pattern over which a transmitter’s
53.

What is the power radiated by the antenna with gain called as?

A. critical power
B. transverse power
C. effective radiated power
D. transmitted power
Answer» C. effective radiated power
Explanation: the power radiated by an antenna with directivity and therefore gain is called the effective radiated power (erp).
54.

What is the radiation pattern of an isotropic radiator?

A. doughnut
B. sphere
C. hemisphere
D. circular
Answer» B. sphere
Explanation: an isotropic radiator is a theoretical point source of electromagnetic energy. the e and h fields radiate out in all directions from the point source, and at any given distance from the point source, the fields form a sphere.
55.

What is the impedance of the folded dipole antenna?

A. 50Ω
B. 100Ω
C. 300Ω
D. 20Ω
Answer» C. 300Ω
Explanation: a popular variation of the half- wave dipole is the folded dipole. like the standard dipole, it is one-half wavelength long. however, it consists of two parallel conductors connected at the ends with one side open at the center for connection to the transmission line. the impedance of this
56.

Which of the following antennas produce a vertical radiation pattern?

A. dipole antenna
B. yagi antenna
C. marconi antenna
D. hertz antenna
Answer» C. marconi antenna
Explanation: the same effect as dipole antenna can be achieved with a one-quarter wavelength antenna or marconi antenna. a vertical dipole with the doughnut-shaped radiation pattern, in which one-half of the pattern is below the surface of the earth. this is called a vertical radiation pattern.
57.

The members of the antenna family which are made of wires of certain value in terms of operating wavelength are called:

A. loop antennas
B. wire antennas
C. dipole antenna
D. slot antennas
Answer» C. dipole antenna
Explanation: wires of half wavelength are termed as dipoles. their radiation resistance is about 73 Ω. if only half of this length is used, then it is called quarter-wave monopole with a radiation resistance of 36.5 Ω.
58.

The antenna in which location of the feed determines the direction of the lobe are:

A. wire antenna
B. loop antenna
C. helical antenna
D. horn antenna
Answer» A. wire antenna
Explanation: in a wire antenna, the location of the feed determines the direction of the lobe and the orientation of the wire determines the polarization. these wires can be thick or thin. thickness of the wire determines the radiation resistance of the antenna.
59.

Based on the size of the loops, loop antennas are classified as small and large loops. This is the only classification of loop antenna.

A. true
B. false
Answer» B. false
Explanation: loop antennas are classified based on various antenna parameters. to name a few, small and large loops, circular and square loops, loops having single or multi turns, loops with turns wound using a single wire or multiple wires.
60.

Antenna that does not belong to the horn antenna family among the following are:

A. pyramidal horn
B. conical horn
C. bi-conical horn
D. none of the mentioned
Answer» D. none of the mentioned
Explanation: all of the above mentioned antennas belong to the horn antenna family. horn antennas may be made of pointed or rounded waveguides. the waveguides may contain disc at an end or some dielectric.
61.

Reflector antennas are widely used to modify radiation patterns of radiating elements.

A. true
B. false
Answer» A. true
Explanation: reflector antennas are used to modify radiation patterns of radiating elements. reflector antennas are classified into two categories. they are passive reflectors and active reflectors. based on the type of the radiating element and the modification in the radiation pattern required, accordingly either active or passive reflectors are chosen.
62.

The pattern of the reflector in a reflector antenna is called:

A. primary pattern
B. secondary pattern
C. reflector pattern
D. none of the mentioned
Answer» B. secondary pattern
Explanation: in a reflector antenna, the feed pattern is called primary pattern and the pattern of the reflector is called secondary pattern. these antennas are widely employed in radars and other types of point to point communication links.
63.

             antennas have gain less than reflector antennas but have more lenient tolerance on surfaces.

A. helical antennas
B. lens antennas
C. array antennas
D. slot antennas
Answer» B. lens antennas
Explanation: lens antennas are complex in nature but are able to scale wider angles. in comparison to reflectors, their gain is 1 or 2 db less, but these have more lenient tolerance on surfaces. these have less rearward reflection, relatively low loss and can be easily shaped to the desired contours.
64.

Lens antennas are classified into two types. One being fast antenna, the other one is:

A. slow antenna
B. delay antenna
C. dynamic antenna
D. none of the mentioned
Answer» B. delay antenna
Explanation: in delay lenses, the electrical path length is increased or the wave is retarded by the lens medium. dielectric lenses and h-plane metal lenses fall in this category.
65.

The antennas which offer high operational bandwidth and the antenna parameters are maintained over a wide range of antennas are called:

A. wide band antennas
B. array antennas
C. parabolic antennas
D. none of the mentioned
Answer» A. wide band antennas
Explanation: in this class of antennas, constancy of impedance and radiation characteristics is maintained over a wide range of frequencies. to be wide band or frequency independent, antennas should expand or contract in proportion to the wavelength.
66.

High directivity required in RADAR communication is satisfied using this type of antennas:

A. wide band antennas
B. antenna arrays
C. slot antennas
D. patch antennas
Answer» B. antenna arrays
Explanation: higher directivity is the requirement in point to point communication. this can be achieved by increasing the size of the antennas in terms of electrical length.
67.

The terminal impedance of a dipole antenna is 710 Ω. The terminal impedance of the slot antenna given the intrinsic impedance of air is 377 Ω is:

A. 100 Ω
B. 50 Ω
C. 25 Ω
D. none of the mentioned
Answer» B. 50 Ω
Explanation: the terminal impedance zs of the slot is given by the relation z 2/ 4z ) zₒ is
68.

When the separation between two lines that carry the TEM wave approaches λ the wave tends to be radiated.

A. true
B. false
Answer» A. true
Explanation: when the separation between two lines that chary the tem wave approaches λ the wave tends to be radiated so that the opened – out line act as an antenna which lunches a free space wave.
69.

An antenna has a field pattern of E (θ) = cos2 θ, θ varies between 0 and 900. Half power beam width of the antenna is:

A. 330
B. 660
C. 12000
D. none of the mentioned
Answer» B. 660
Explanation: half power beam width of the antenna is obtained by equating the field pattern of the antenna to 0.707 (half power point) and finding θ. 2θ gives the value of beam width. solving the given problem in the same flow, half power beam width of the antenna is 660.
70.

Power radiated from an antenna per unit solid angle is called radiation intensity.

A. true
B. false
Answer» A. true
Explanation: power radiated from an antenna per unit solid angle is called radiation intensity. unit of radiation intensity is watts per steridian or per square degree.
71.

Antennas are bidirectional devices.

A. true
B. false
Answer» A. true
Explanation: 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.
72.

Which of the following is false regarding Antenna array?

A. directivity increases
B. directivity decreases
C. beam width decreases
D. gain increases
Answer» B. directivity decreases
Explanation: 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.
73.

Electrical size of antenna is increased by which of the following?

A. antenna array
B. decreasing the coverage area
C. increasing the coverage area
D. using a single antenna
Answer» A. antenna array
Explanation: 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.
74.

For long distance communication, which of the property is mainly necessary for the antenna?

A. high directivity
B. low directivity
C. low gain
D. broad beam width
Answer» A. high directivity
Explanation: 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.
75.

Which of the following is false about the single antenna for long distance communication?

A. enlarging may create side lobes
B. no side lobes
C. high directivity is required
D. high gain is required
Answer» B. no side lobes
Explanation: 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.
76.

The electrical size of antenna is increased by antenna array to avoid size lobes compared to single antenna.

A. true
B. false
Answer» A. true
Explanation: 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.
77.

Total resultant field obtained by the antenna array is given by which of following?

A. vector superposition of individual field from the element
B. maximum field from individual sources in the array
C. minimum field from individual sources in the array
D. field from the individual source
Answer» A. vector superposition of individual field from the element
Explanation: 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.
78.

If the progressive shift in antenna array is equal to zero then it is called                    

A. broad side
B. end-fire
C. yagi-uda
D. fishbone antenna
Answer» A. broad side
Explanation: the total phase difference of the fields is given by Ѱ=kdcosθ+β
79.

What is the progressive phase shift of the end-fire array?

A. 0
B. 90
C. 180
D. 60
Answer» C. 180
Explanation: 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°.
80.

Which of the following statement about antenna array is false?

A. field pattern is the product of individual elements in array
B. field pattern is the sum of individual elements in array
C. resultant field is the vector superposition of the fields from individual elements in array
D. high directivity can be achieved for long distance communications
Answer» B. field pattern is the sum of individual elements in array
Explanation: 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.
81.

                               are used in the final stages of radar and radio transmitters to increase the radiated power level.

A. power amplifiers
B. oscillators
C. transistors
D. attenuators
Answer» A. power amplifiers
Explanation: 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.
82.

Important factors to be considered for power amplifier design are:

A. efficiency
B. gain
C. thermal effect
D. all of the mentioned
Answer» D. all of the mentioned
Explanation: 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.
83.

1 MICROWAVE PASSIVE COMPONENTS: DIRECTIONAL COUPLER, POWER DIVIDER, MAGIC TEE ATTENUATOR, RESONATOR

A. true
B. false
Answer» A. true
Explanation: 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.
84.

Gain of power amplifiers                      with increase in operating frequency.

A. increases
B. decreases
C. increases exponentially
D. decreases exponentially
Answer» B. decreases
Explanation: 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.
85.

                       amplifiers are linear circuits, where the transistor is biased to conduct over the entire range of the input signal cycle.

A. class a amplifiers
B. class b amplifiers
C. class c amplifiers
D. none of the mentioned
Answer» A. class a amplifiers
Explanation: 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%.
86.

A class B amplifier consists of                 transistors in order to conduct the input signal over the entire cycle.

A. 1
B. 2
C. 4
D. 6
Answer» B. 2
Explanation: 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.
87.

Power amplifiers in the increasing order of efficiency is:

A. class a, b, c
B. class c, a, b
C. class b, a, c
D. efficiency of all the 3 amplifiers is the same
Answer» A. class a, b, c
Explanation: 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
88.

Behavior of a transistor in power amplifiers is unpredictable at all input signal levels.

A. true
B. false
Answer» B. false
Explanation: 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.
89.

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

A. 25%
B. 50%
C. 75%
D. 35%
Answer» A. 25%
Explanation: efficiency of a power amplifier is (pout- pin)/ pdc substituting the given values in the above expression, efficiency of the power amplifier is 25%.
90.

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:

A. 400 mw
B. 225 mw
C. 229 mw
D. 240 mw
Answer» C. 229 mw
Explanation: 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.
91.

GaAs is used in the fabrication of GUNN diodes because:

A. gaas is cost effective
B. it less temperature sensitive
C. it has low conduction band electrons
D. less forbidden energy gap
Answer» D. less forbidden energy gap
Explanation: 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.
92.

In a GaAs n-type specimen, the current generated is constant irrespective of the electric filed applied to the specimen.

A. true
B. false
Answer» B. false
Explanation: in a gaas n-type specimen, when the electric field applied reaches a threshold value of eth, the current in the specimen becomes suddenly oscillatory and with respect to time and these oscillations are in the microwave frequency range. this effect is called gunn effect.
93.

When the electric field applied to GaAs specimen is less than the threshold electric field, the current in the material:

A. increases linearly
B. decreases linearly
C. increases exponentially
D. decreases exponentially
Answer» A. increases linearly
Explanation: when the electric field applied is less than the threshold value of electric field, the electrons jump from the valence band to the primary valley of the conduction band and current increases linearly with electric field.
94.

GaAs is used in fabricating Gunn diode. Gunn diode is:

A. bulk device
B. sliced device
C. made of different type of semiconductor layers
D. none of the mentioned
Answer» A. bulk device
Explanation: a gunn diode is a bulk device, that is, it does not contain any junction but it is a slice of n-type gaas. p- type gaas does not exhibit gunn effect. hence it is a reversible and can be operated in both directions.
95.

The electrodes of a Gunn diode are made of:

A. molybdenum
B. gaas
C. gold
D. copper
Answer» A. molybdenum
Explanation: gunn diode is grown epitaxially onto a gold or copper plated molybdenum electrode, out of gallium arsenide doped with silicon, tellurium or selenium to make it n-type.
96.

When either a voltage or current is applied to the terminals of bulk solid state compound GaAs, a differential              is developed in that bulk device.

A. negative resistance
B. positive resistance
C. negative voltage
D. none of the mentioned
Answer» A. negative resistance
Explanation: when either a voltage or current is applied to the terminals of a sample of bulk solid state compound formed by group 5 and 3 elements of periodic table, a differential resistance is developed in the bulk device. this fundamental concept is called rwh theory.
97.

The number of modes of operation for n type GaAs is:

A. two
B. three
C. four
D. five
Answer» C. four
Explanation: n-type gaas used for fabricating gunn diode has four modes of operation. they are gunn oscillation mode, limited space charge accumulation mode, and stable amplification mode bias circuit oscillation mode.
98.

The free electron concentration in N-type GaAs is controlled by:

A. effective doping
B. bias voltage
C. drive current
D. none of the mentioned
Answer» A. effective doping
Explanation: the free electron concentration in n-type gaas is controlled through effective doping so that they range from 1014 to 1017 per cc at room temperature. the typical specimen of n-type gaas has the dimensions 150 µm by 150 µm.
99.

The modes of operation of a Gunn diode are illustrated in a plot of voltage applied to the Gunn diode v/s frequency of operation of Gunn diode.

A. true
B. false
Answer» B. false
Explanation: a graph of plot of product of frequency and the length of the device plotted along y-axis versus the product of doping concentration and length along x- axis. these are the parameters on which the four modes of operation of gunn diode are explained.
100.

The mode of operation in which the Gunn diode is not stable is:

A. gunn oscillation mode
B. limited space charge accumulation mode
C. stable amplification mode
D. bias circuit oscillation mode
Answer» A. gunn oscillation mode
Explanation: in gunn oscillation mode, the device is unstable due to the formation of accumulation layer and field domain. this high field domain moves from cathode to anode.
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