GaAs varactor tuned filter for low power applications

A five-pole varactor-tuned filter with a 5% pass-band operating at 1.9 GHz is proposed. The tunability is realized by reverse-biased GaAs diodes loading the resonators, which are formed by a section of multicoupled microstrip lines. A measured center frequency shift of 200 MHz (10% tunability) was made at 22 V DC bias. The insertion loss varies in the range of 6-4.5 dB, while matching is better than 12 dB. The output IP3 range is -1.6 dBm at the lowest bias, increasing to 24 dBm at the highest bias voltage, and the temperature stability is about 1.8% (from -50° to 125°C) at 1 V and 0.5% at 10 V.