Aperture Antennas Questions and Answers

Answer: A

Any reflecting surface acts as a second source whose contribution adds vectorially to the direct one, producing ripples in the measured pattern and badly falsifying the side lobes. Absorber, elevated geometry and time gating are the usual defences. Reflections do not significantly raise receiver noise, do not alter the antenna's terminal impedance at these levels, and cause no heating. Controlling the measurement environment is as much a part of antenna engineering as designing the antenna.

Answer: B

A reflected path is longer than the direct one, so transforming the swept frequency response to the time domain and windowing out the late arrivals removes the reflection. It allows respectable measurements in rooms that are far from anechoic. Speed, synchronisation and averaging are separate benefits of modern instrumentation. Using the time of arrival to separate wanted from unwanted signals is the same principle radar uses, applied here to a measurement problem.