Aerial isolation: a study of the interaction between co-sited aerials

The increased complexity of modern aircraft has resulted in a proliferation of aerials sited in close proximity to one another, a trend more marked in military types, which makes it even more necessary to ensure compatibility of working in a crowded r.f. spectrum. The paper presents the investigations that have been made to determine the degree of isolation between transmitting and receiving aerials in aircraft within the frequency range 30 to 1250 MHz. From measurements using cylinders, ground planes, helicopters and fixed wing aircraft, empirical formulae for the calculation of aerial-to-aerial isolation have been derived. Investigations have also been carried out to determine the amplitude of the harmonics generated by airborne transmitters. The results obtained from both these aspects of the work are discussed.