Question 1
A dipole antenna is also called as?
A. Marconi antenna
B. Yagi antenna
C. Bidirectional antenna
D. Hertz antenna
View Answer
Answer: Option D
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.
Question 2
Parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element is called _______
A. Array element
B. Director element
C. Reflector element
D. Driven element
View Answer
Answer: Option C
Explanation:
The reflector, a parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element, is spaced from the driven element by a distance of 0.15λ to 0.25λ. When the signal radiated from the dipole reaches the reflector, it induces a voltage into the reflector and the reflector produces some radiation of its own creating a highly focused beam in the direction of the driven element.
Question 3
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
Answer: Option B
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.
Question 4
The radiation pattern of a half-wave dipole has the shape of a ______
A. Doughnut
B. Sphere
C. Hemisphere
D. Circular
View Answer
Answer: Option A
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.
Question 5
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
Answer: Option A
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.
Question 6
What does the beam width of an antenna tell us?
A. Signal strength
B. Signal power
C. Directivity
D. Degradation
View Answer
Answer: Option C
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.
Question 7
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
Answer: Option D
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.
Question 8
What is the beam width for a half wave dipole antenna?
A. 90°
B. 180°
C. 50°
D. 250°
View Answer
Answer: Option A
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.
Question 9
What is the impedance of the folded dipole antenna?
A. 50Ω
B. 100Ω
C. 300Ω
D. 20Ω
View Answer
Answer: Option C
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.
Question 10
What is the length of the shortest element in the yagi antenna?
A. One quarter the wavelength of the highest frequency
B. One quarter the wavelength of the lowest frequency
C. One half the wavelength of the highest frequency
D. One half the wavelength of the lowest frequency
View Answer
Answer: Option C
Explanation:
The lengths of the driven elements vary from long to short and are related logarithmically. The longest element has a length of one-half wavelength at the lowest frequency to be covered, and the shortest element is one-half wavelength at the higher frequency. The spacing is also variable.
Question 11
In a parasitic array antenna, the conductors that are not connected to the transmission line is called as?
A. Driven element
B. Parasitic elements
C. Extra elements
D. Array elements
View Answer
Answer: Option B
Explanation:
A parasitic array consists of a basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line. These extra conductors are referred to as parasitic elements, and the antenna itself is referred to as the driven element.
Question 12
In a parasitic array the elements are shorted if they are connected to a conducting beam.
A. True
B. False
View Answer
Answer: Option B
Explanation:
The boom does not have to be an insulator. Because there is a voltage null at the center of a one-half wavelength conductor at the resonant frequency, there is no potential difference between the elements and so they can all be connected to a conducting boom with no undesirable effect. In other words, the elements are not “shorted together.”
Question 13
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
Answer: Option C
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.
Question 14
What is the radiation pattern of an isotropic radiator?
A. Doughnut
B. Sphere
C. Hemisphere
D. Circular
View Answer
Answer: Option B
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.
Question 15
What is the use of loading coil?
A. Correcting resonance to a desired frequency
B. Increasing the antenna gain
C. Sideband suppression
D. Increasing the range of the antenna
View Answer
Answer: Option A
Explanation:
When a vertical antenna is made less than one-quarter wavelength, the practical effect is a decreased inductance. The antenna no longer resonates at the desired operating frequency, but at a higher frequency. To compensate for this, a series inductor, called a loading coil, is connected in series with the antenna coil. The loading coil brings the antenna back into resonance at the desired frequency.
Question 16
Which of the following antennas produce a vertical radiation pattern?
A. Dipole antenna
B. Yagi antenna
C. Marconi antenna
D. Hertz antenna
View Answer
Answer: Option C
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.
Question 17
Which of the following is not one of the types of driven array antenna?
A. Rectilinear antenna
B. Broadside antenna
C. End fire antenna
D. log periodic antenna
View Answer
Answer: Option A
Explanation:
Each element in a driven array antenna receives RF energy from the transmission line, and different arrangements of the elements produce different degrees of directivity and gain. The three basic types of driven arrays are the collinear, the broadside, and the end-i re. A fourth type is the wide-bandwidth log-periodic antenna.
Question 18
Why is the boom of the yagi antenna connected to a metal mast and electrical ground?
A. Better signal directivity
B. Increased bandwidth
C. Lightning protection
D. To avoid short circuiting
View Answer
Answer: Option C
Explanation:
The centers of the parasitic elements are neutral electrically; these elements can be connected directly to the boom. For the best lightning protection, the boom can then be connected to a metal mast and electrical ground.
Question 19
Why is top hat added to antennas?
A. To increase capacitance
B. Increasing the antenna gain
C. Sideband suppression
D. Increasing the range of the antenna
View Answer
Answer: Option A
Explanation:
A top hat is a structure that increases the capacitance to surrounding items, bringing the antenna back into resonance. Obviously, such an arrangement is too top-heavy and inconvenient for portable and mobile antennas. However, it is sometimes used in larger fixed antennas at lower frequencies.