Simple Directive High-frequency Antennas

Author: Edmund A. Laport

In point-to-point communication over fixed circuits it is usually desirable to employ varying amounts of directivity for transmitting or receiving. The reasons for using directivity are:

Transmitting. Power gain in the preferred direction in order to

1. Economize on transmitter power

2. Increase the signal-to-noise ratio at the receiver

3. Increase the margins of reliable operation

4. Reduce interference in other directions

5. Reduce signal distortion due to multipath transmission Receiving.

1. To obtain better signal-to-noise and signal-to-interference ratios when the disturbances come from other directions than the desired signals

2. To discriminate against multipath signals arriving at different vertical angles

3. To give a larger signal input voltage at the receiver

Additional directivity over that which is typical of a single horizontal dipole can be obtained with director and reflector elements associated with the dipole and fed directly or parasitically.

Broadside dipole arrays have a valuable property - their horizontal and vertical patterns can be separately controlled. The vertical directivity is controlled by the height and the number of radiators in the vertical stack, their spacings, and their current distributions. The horizontal directivity is controlled by the number of radiators in the horizontal line, their spacings, and their current distributions. End-fire and long-wire radiators and arrays lack the feature of independent control of vertical and horizontal patterns.