This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Antenna Family”.
1. 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
View Answer
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.
2. 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
View Answer
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.
3. 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
View Answer
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.
4. 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
View Answer
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.
5. Patch antennas are the antennas of small size and are made of:
a) Strip line
b) Microstrip lines
c) Coaxial cables
d) Rectangular waveguide
View Answer
Explanation: Patch antennas are microstrip antennas that can be of any shape. Patch antennas can be aperture-coupled fed or proximity fed. For obtaining circular polarization, a patch may also be doubly fed.
6. Reflector antennas are widely used to modify radiation patterns of radiating elements.
a) True
b) False
View Answer
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.
7. 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
View Answer
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.
8. ______ 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
View Answer
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.
9. 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
View Answer
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.
10. 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
View Answer
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.
11. 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
View Answer
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. When much high directivity is required, antenna arrays are used.
12. 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
View Answer
Explanation: The terminal impedance ZS of the slot is given by the relation Z02/ 4Zd) Zₒ is the intrinsic impedance of the medium and ZD is the terminal impedance of the dipole. Substituting the given values in the above equation, the terminal impedance of sot is 50 Ω.
13. If the length of aperture in a pyramidal horn antenna is 10cm and δ for the design is 0.25. Then, the flaring angle of the pyramidal horn is:
a) 30⁰
b) 25.4⁰
c) 45⁰
d) 60⁰
View Answer
Explanation: The flaring angle of pyramidal horn is given by 2cos-1(L/L+δ). Substituting the values of L and δ, flaring angle is 25.4⁰.
14. If the directivity of a square corner receiving antenna is 20 and operating at a wavelength of 0.25m, the effective aperture of a square corner antenna is:
a) 0.4 m2
b) 0.2 m2
c) 0.1 m2
d) None of the mentioned
View Answer
Explanation: Given the directivity of the antenna, effective aperture of the antenna is given by Dλ2/4π. substituting the given values of the variables; the effective aperture of the antenna is 0.4 m2.
Sanfoundry Global Education & Learning Series – Microwave Engineering.
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