A survey of external and suppressed aircraft aerials for use in the high-frequency band

Abstract

External wire aerials, which are usually employed at frequencies below 20 Mc/s for radio aids on aircraft, are not preferred on high-speed aircraft because of their drag and general mechanical unsuitability. It becomes necessary to include the aerials within the aircraft skin, when they are usually referred to as suppressed aerials.In the paper, information on well-known external wire aerials, such as fixed inclined wires (long and short), inverted-L wires, trailing wires and shunt-wire-fed wings, is compared with that obtained with various suppressed aerials. Some of the suppressed aerials have performances which compare favourably with the external wire types and in certain respects have apparently better electrical characteristics. In particular, aerials which are folded or near-end fed, or those which involve an insulated stabilizer unit, have a wide bandwidth and are reasonably efficient. The impedance characteristics of some of the suppressed aerials are such as to make their use suitable where it is required to cover frequencies lower than the h.f. band.For h.f. suppressed aerials, where the wavelength is comparable to the aircraft dimension, the view is held that an efficient suppressed aerial will require the excitation of either the whole aircraft or a large part of it. Various methods of excitation are discussed and experimental evidence is given. Since the stabilizer is usually the only vertical component, its use is contemplated for vertical polarization; similarly, the wings and horizontal units of the aircraft are considered for horizontal polarization.Measurements of the electrical characteristics of aircraft aerials present considerable difficulties. They are not often satisfactory on a grounded aircraft, and flights are very uneconomical for preliminary experiments. In order to overcome these difficulties, the method of scaling aerials on scale-model aircraft is widely used to determine the performance of both external and suppressed aerials. Some of the suppressed types of aerial which have shown satisfactory characteristics obtained with the scale models have been installed in aircraft, and successful long-range flights using these aerials in the 2–20 Mc/s communication band have been made.