ANSWERS TO QUESTIONS Q1. THROUGH Q18.

3-19 LENS ANTENNAS use a COLLIMATING LENS to force the spherical components of a wavefront into parallel (focused) paths by delaying or accelerating portions of the wavefronts, as shown in the illustration. An ANTENNA ARRAY is a set of antenna elements and may be one of two basic types, the DRIVEN ARRAY or the PARASITIC ARRAY. FREQUENCY-SENSITIVE ANTENNAS use frequency-sensitive slots as radiation sources to achieve directivity. The angle at which the radiated beam leaves the antenna is determined by the frequency of the radiated energy. Currently the most common frequency-sensitive antennas use this feature to achieve elevation coverage while azimuth coverage is achieved by rotating the antennas. New systems will use stationary frequency-sensitive antennas to achieve both azimuth and elevation coverage. ANSWERS TO QUESTIONS Q1. THROUGH Q18. A-1. Operating principles and electrical characteristics. A-2. Power gain or power ratio. A-3. Standing-wave ratio (swr).