Variable bandwidth, wide tunable frequency, voltage tuned filter

This article discusses the development of an electronically tuned filter capable of a wide tunable frequency range and simultaneous 3-dB bandwidth variations at any frequency within its tuning range. Varactor-tunable filters are designed using high-dielectric, soft-substrate material for printed resonators as well as also high-Q ceramic resonators, and their test data are compared. Greater than 50% tuning range with low insertion loss at a center frequency in the L and S frequency bands is demonstrated with a 4:1 change in 3-dB bandwidth—30 to 120 MHz for printed resonators and 14 to 46 MHz for ceramic resonators. The concept of tuning a filter's 3-dB bandwidth with voltage is demonstrated and the effect of the bandwidth tuning elements on the tunable filter performance is discussed.