_______________________________________________________________________ Antennas
consists of two separate arrays (one high frequency and one low frequency
antenna array) mounted on one frame. The various elements are indicated in
the figure. The high-frequency (HF) array consists of one reflector, one driven
element, and two directors; the low-frequency (LF) array has the same
arrangement with one less director. The lengths of the elements in the high-
frequency array are shorter than those in the low-frequency array. The
physical lengths of the elements in the individual arrays are equal, but the
electrical lengths can be varied by means of the tuning stubs at the center of
the elements. The array can be rotated in any desired direction by a remotely
controlled, electrically driven, antenna rotator.
Figure 4-34. Typical Parasitic Array Used for Transmitting and Receiving
4-158. In this section we cover some special communications and radar
antennas. Some of these antennas we touch on only briefly because they are
covered thoroughly in other courses.
4-159. Previously discussed antennas operate with standing waves of
current and voltage along the wires. This section deals principally with
antenna systems in which the current is practically uniform in all parts of
the antenna. In its basic form, such an antenna consists of a single wire
grounded at the far end through a resistor. The resistor has a value equal to
4-47
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