Abstract
An engineering study has been made of the factors influencing the overall radiation efficiency of electrically short h.f. groundwave aerial systems, with particular reference to physically restricted tactical portable and mobile environments. A discussion of the basic theoretical limitations on the radiation efficiency of such aerial systems has emphasised several factors not previously sufficiently recognised as important in realising an optimum aerial system within given practical constraints. A detailed, practical investigation has been carried out using full-scale aerial systems over real ground and straightforward techniques developed for assessing relative performance. This field study has identified several mechanisms peculiar to small aerial systems, the most dramatic being that associated with radial wire resonance. It has been clearly shown that radial wire resonance can influence the systems. efficiency very significantly, but, that if properly appreciated and employed, can be used to advantage. A further theoretical analysis of the effect on v.s.w.r. and radiated power level due to aerial sway, particularly relevant to a mobile environment, has demonstrated that a dynamic improvement of up to 6.5dB to be theoretically possible. Whilst a rigorous theoretical analysis of the effect of the proximity of a lossy ground has proved to be a formidible task, a simple experimental technique has been described, employing the radial wire resonance phenomena, for the direct determination of the effective bulk dielectric constant of the ground. This technique may also be expanded to determine the effective ground conductivity. An engineering procedure for the design of an optimum efficiency aerial system, within given constraints, including the aerial tuning unit has been discussed and 'guidelines' for field operators established.