A Very-High-Frequency Ultra-High-Frequency Tail-Cap Antenna

A description is given of a broad-band vhf-uhf antenna for a small, single-engine type of aircraft consisting of the vertical stabilizer that is tip-fed by the metal tail cap. The resulting antenna covers the frequency range of 100 to 400 mc, is vertically polarized, and has radiation patterns that are essentially omnidirectional. It is a zero-drag type of antenna that is very adaptable to aircraft production techniques. The tail cap, together with the rest of the vertical stabilizer, performs as a vertical sleeve-fed stub on an unsymmetrical ground plane. For this reason, the antenna radiation fields are not perfectly omnidirectional, but they are adequate for two-way communication in the frequency range 100 to 400 mc, and in this range the standing wave ratio on RG-8/U 50-ohm coaxial cable is less than 2 to 1. The predicted radiation field-strength patterns for a specified transmitter power are calculated from measured radiation field patterns of the scale-model aircraft and full-scale standing-wave ratio measurements.