
327Microwave Antennas
exhibits many of the characteristics of a conventional dipole antenna. When
arranged in arrays, a high degree of directivity can be obtained. Their beams
can scan a volume of space by changing either the frequency or phase of the
signal driving the antenna elements.
9.3.4 Lens Antennas
Lenses can be used for radio waves just as for light. The structure of a lens
antenna is a bit complex than that of the reector antenna. Their gain is also
1 or 2 dB less than that of reectors. These, however, can scan wider angles
(a) (b) (c) (d)
FIGURE 9.8
Shapes of slot antennas. (a) Vertical slot, (b) horizontal slot, (c) circular slot ...