This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Types of Antenna – 1”.
1. A dipole antenna is also called as?
a) Marconi antenna
b) Yagi antenna
c) Bidirectional antenna
d) Hertz antenna
View Answer
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.
2. The impedance at the center of the antenna is known as?
a) Characteristic impedance
b) Radiation resistance
c) Transmission impedance
d) Recovery resistance
View Answer
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.
3. 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
View Answer
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.
4. 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
View Answer
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.
5. The radiation pattern of a half-wave dipole has the shape of a ______
a) Doughnut
b) Sphere
c) Hemisphere
d) Circular
View Answer
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.
6. What is the beam width for a half wave dipole antenna?
a) 90°
b) 180°
c) 50°
d) 250°
View Answer
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.
7. What does the beam width of an antenna tell us?
a) Signal strength
b) Signal power
c) Directivity
d) Degradation
View Answer
Explanation: The measure of an antenna’s directivity is beam width, the angle of the radiation pattern over which a transmitter’s energy is directed or received. Beam width is measured on an antenna’s radiation pattern.
8. 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
View Answer
Explanation: The power radiated by an antenna with directivity and therefore gain is called the effective radiated power (ERP). The ERP is calculated by multiplying the transmitter power fed to the antenna Pt by the power gain Ap of the antenna.
9. What is the radiation pattern of an isotropic radiator?
a) Doughnut
b) Sphere
c) Hemisphere
d) Circular
View Answer
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.
10. What is the impedance of the folded dipole antenna?
a) 50Ω
b) 100Ω
c) 300Ω
d) 20Ω
View Answer
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 popular antenna is 300 V, making it an excellent match for the widely available 300-V twin lead.
11. Which of the following antennas produce a vertical radiation pattern?
a) Dipole antenna
b) Yagi antenna
c) Marconi antenna
d) Hertz antenna
View Answer
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.
Sanfoundry Global Education & Learning Series – Avionics.
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