High-power Electronic Tuning

Tunable HF/VHF filters capable of operating at high power levels are needed for preventing a jammer from interfering with nearby friendly communications, high-speed antenna tuners, and output filters for high-efficiency power amplifiers (PAS). Filter systems presently employ either relays or pin-diode switches to select one filter from a bank of filters that spans the operating frequency range. Tuning systems similarly select combinations of inductors or capacitors. The problems with the present approach include: slow switching, especially if relays are used; size and weight; imperfect match (SWR) in band; use of inefficient class-B PAs that require no, tuning; and use of low-efficiency resistively loaded antennas. High-power electronic tuning can therefore benefit a variety of military and civilian applications. The proposed program will investigate the feasibility of high-power electronically tuned filters. The investigation includes: filter topology, semiconductors that exhibit voltage-variable capacitance, variable ceramic-chip capacitors, and variable toroidal inductors. The proposed program brings together experts on both RF-power circuits (Dr. Frederick H. Raab) and semiconductors (Dr. Krishna Shenal). Use of fewer filters makes possible reductions in size, weight, and cost. Precise tuning boosts the efficiency of RF-power amplifiers in general and makes high-efficiency (class-D, -E) amplifiers readily useable. Electronic tuning simplifies antenna tuners and makes possible the use of antennas with better gain.