HF array simulations

The Ionospheric Research Instrument (IRI) is an HF transmitting array facility currently being constructed in Gakona, Alaska, as part of the HF Active Auroral Research Program (HAARP). This program will result in an ionospheric heater facility in the auroral region, dedicated to the exploration of ionospheric phenomena that can be induced by ionospheric modification. For an HF array where the transmitter output stage is a tuned high power vacuum tube, the stability and tunability of each transmitter tube presents a complex problem because of array coupling. We have modeled a (3/spl times/3) HF array with transmitters, baluns, antenna matching units, and antennas. Transmitter models were based on EIMAC 10 kW tetrodes with tuning networks, and antenna models were simply S-parameter files obtained from NEC calculations as well as measurements on 7/spl times/7 and 3/spl times/3 cross dipole arrays. The simulations were performed using HP-EEsof Libra, which can accommodate up to 99 ports, where each port is an element of the array. We present the results characterizing the stability conditions for operating the transmitters in a highly coupled antenna array environment.