Aircraft Antenna-Coupled Interference Analysis

A mathematical model specifically for aircraft antenna-to-antenna electromagnetic interference analysis has been developed. Basically, the model consists of a two-level analysis: 1) frequency coincidence to indicate potential interference and 2) a detailed analysis involving power levels and receiver thresholds. A receiver and transmitter are selected from the input data, and their frequency bands are compared for coincidence. The frequency comparison includes the fundamental and significant harmonics as specified for the transmitter. If frequency coincidence is found, indicating potential interference, the worst-case power level at the receiver from the transmitter is computed using the shortest path along the aircraft surface. When the path is around the fuselage, allowance is made for shading (diffraction) effects. The power received is compared with the receiver threshold to obtain an EMI margin. Each case with an EMI margin above a specified value is listed in the computer output as are the frequencies involved and the computational method used. Margins are computed for each antenna combination of the two systems. This process is repeated for each transmitter and receiver on the aircraft. The method of analysis is presented with particular emphasis on the techniques used to obtain propagation paths and shading factors.