Modeling multiple HF antennas on the C-130/Hercules aircraft - part II

Long-range transport aircraft such as the C-130/Hercules require reliable HF communication systems for their global missions. In some cases dual HF systems are installed using two separate antennas, in a SIMOP mode: one antenna for transmitting and the other for receiving, at arbitrary frequencies over the 2-30 MHz HF frequency range. Candidate antennas for such HF systems are probes on the vertical stabilizer or the wingtips and dorsal or wing-root notch antennas. Previous work has modeled the HF performance of these antennas by executing spectral sweeps of models at 0.1 MHz increments using the NEC4 and MBC computer codes. These results were also correlated with scale model radiation pattern and impedance measurements. In this paper the results of explicit modeling of the SIMOP mode are presented for the candidate antenna pairs. The receive antenna terminals are terminated in 50 ohms and transmit and receive currents are extracted from the solution file and each pair is plotted vs. frequency. It is seen that peaks in the antenna coupling correspond to the resonant peaks in plots of impedance reported earlier. Insights provided by current distribution plots on the wire-grid model for each antenna allow the degree of antenna coupling to be well understood. This exceptional use of the "CEM virtual antenna range" can lead to very cost-effective HF SIMOP installation designs.