High-frequency and high-Q tunable active filters

Investigation of the performance of classical second-order bandpass active filters has shown that since they use low-gain elements, they can be divided into two classes at high frequencies: low-selectivity stable filters and low-stability selective filters. The author presents structures that realize a good compromise between both classes, so that high Q can be achieved with good stability. Verifications have been carried out with experimental Si hybrid high-frequency filters and with computer simulations of GaAs microwave integrated filters. The center frequency of the GaAs filters is tuned with MESFETs used as voltage-controlled resistors and can exceed 2 GHz.>