Key Topic 63: Antenna Theory

Question 1

3-63J1: Which of the following could cause a high standing wave ratio on a transmission line?

A. Excessive modulation.
B. An increase in output power.
C. A detuned antenna coupler.
D. Low power from the transmitter.

Answer 1

C. A detuned antenna coupler.

Question 2

3-63J2: Why is the value of the radiation resistance of an antenna important?

A. Knowing the radiation resistance makes it possible to match impedances for maximum power transfer.
B. Knowing the radiation resistance makes it possible to measure the near-field radiation density from transmitting antenna.
C. The value of the radiation resistance represents the front-to-side ratio of the antenna.
D. The value of the radiation resistance represents the front-to-back ratio of the antenna.

Answer 2

A. Knowing the radiation resistance makes it possible to match impedances for maximum power transfer.

Question 3

3-63J3: A radio frequency device that allows RF energy to pass through in one direction with very little loss but absorbs RF power in the opposite direction is a :

A. Circulator.
B. Wave trap.
C. Multiplexer.
D. Isolator.

Answer 3

D. Isolator.

Question 4

3-63J4: What is an advantage of using a trap antenna?

A. It may be used for multiband operation.
B. It has high directivity in the high-frequency bands.
C. It has high gain.
D. It minimizes harmonic radiation.

Answer 4

A. It may be used for multiband operation.

Question 5

3-63J5: What is meant by the term radiation resistance of an antenna?

A. Losses in the antenna elements and feed line.
B. The specific impedance of the antenna.
C. The resistance in the trap coils to received signals.
D. An equivalent resistance that would dissipate the same amount of power as that radiated from an antenna.

Answer 5

D. An equivalent resistance that would dissipate the same amount of power as that radiated from an antenna.

Question 6

3-63J6: What is meant by the term antenna bandwidth?

A. Antenna length divided by the number of elements.
B. The frequency range over which an antenna can be expected to perform well.
C. The angle between the half-power radiation points.
D. The angle formed between two imaginary lines drawn through the ends of the elements.

Answer 6

B. The frequency range over which an antenna can be expected to perform well.