A MESFET-controlled X-band active bandpass filter

A MESFET-controlled active bandpass filter that was developed for use with X-band frequencies is reported. This filter loss is compensated for by the negative resistance generated by a MESFET. The series tank circuit of the filter includes another MESFET that is controlled either by a gate-to-source bias or by a semiconductor laser illumination. The center frequency of the passband can be shifted by 75 MHz with an accompanying bandwidth change from 6 MHz to 17 MHz when the gate-to-source voltage of the tuning MESFET is varied. Laser illumination of this MESFET shifts the center frequency of the filter by 57 MHz with a bandwidth change from 6.5 MHz to 10 MHz.<>