Frank H. Sanders

Abstract: This Technical Memorandum describes a process for selecting an appropriate antenna for monitoring radio signals from airborne transmitters. A mathematical formula for the optimal receiver antenna gain is presented. This formula takes into account the factors of minimal required signal-to-noise ratio of signals in a monitoring receiver, airborne radio transmitted power and antenna gain, airborne radio height and resulting maximal line-of-sight coverage, free-space propagation loss, airborne radio signal bandwidth, monitoring system bandwidth, and the sensitivity of the monitoring system’s receiver. The optimal monitoring antenna gain is calculated as a function of elevation angle above the local horizon. That function is used to select an antenna type that will receive signals from as many airborne radios as possible. A worked example of the selection process is presented. Although it is assumed that a terrestrial system will be used for monitoring, the process can be applied to antennas for marine and airborne monitoring systems as well.

Keywords: antenna gain; RF measurement; airborne signals; RF monitoring

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