HAM HAM Radio Extra Class Test Antenna Theory and Design Questions and Answers 2

Question 1

What is the approximate radiation resistance of a half-wave dipole antenna in free space?

Accepted Answer

73 ohms

Answer

50 ohms

Answer

36 ohms

Answer

100 ohms

Question 2

What type of antenna pattern does a collinear array produce?

Accepted Answer

Omnidirectional with gain concentrated at low elevation angles

Answer

Highly directional in one direction

Answer

Bidirectional figure-eight pattern

Answer

Hemispherical pattern above ground

Question 3

What is the primary advantage of a log-periodic dipole array (LPDA)?

Accepted Answer

Wide bandwidth with relatively constant gain and impedance

Answer

Extremely high gain on a single frequency

Answer

Circular polarization across all bands

Answer

Elimination of feedline losses

Question 4

How does the beamwidth of a parabolic dish antenna change as the dish diameter increases relative to wavelength?

Accepted Answer

Beamwidth decreases

Answer

Beamwidth increases

Answer

Beamwidth remains the same

Answer

Beamwidth oscillates unpredictably

Question 5

What is the effect of adding a reflector element to a Yagi-Uda antenna?

Accepted Answer

It increases forward gain and improves the front-to-back ratio

Answer

It decreases the antenna impedance to near zero

Answer

It eliminates all sidelobes from the radiation pattern

Answer

It converts the antenna to circular polarization

Question 6

What is the purpose of a gamma match on a Yagi antenna?

Accepted Answer

To match the low impedance of the driven element to a 50-ohm feedline

Answer

To increase the bandwidth of the antenna by 50%

Answer

To eliminate the need for a balun

Answer

To add circular polarization capability