Reduction of Intermodulation in Air Ground Communication

Abstract

The increase in the number of air/ground communication stations has resulted in large frequency of radio interference, which may deteriorate air traffic safety. This paper deals with suppression of intermodulation of transmitters, the largest among factors giving rise to the interference. Following methods are considered to be effective for the purpose:

(1) suppression of the mutual coupling between antennas

and

(2) improvement of the intermodulation characteristics.

With regard to item (1), rough estimation is tried here for the practical limit of the amount of coupling for various site conditions. The latter item is also studied by employing the linear amplifire which yields a reduction of about 6 dB and further, the application of the right-angled hybrid connection with coaxial cables gives an additional improvement of 13 dB. Thus, the study allows to establish a siting standard for air/ground communication.