McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 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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