Continuous frequency and bandwidth tunable combline cavity bandpass filters with internally mounted motors.

Novel design methods for implementing continuous centre-frequency and bandwidth tunability are reported. Coupling bandwidths are tuned through the mechanical rotation of a metallic plate suspended between resonators. Centre-frequency tuning is achieved via the vertical actuation of a moving part mounted within each resonator. In addition, each resonator and transformer is designed so that motors can be housed within them - adding tunability without compromising the overall filter volume. A second-order filter, based on combline cavity structures, capable of bandwidth tunability of 49-67 MHz for all centre frequencies in the range of 1.751-1.998 GHz is presented. Passband insertion loss is kept below 1.2 dB for all tuning states with return loss above 10 dB. A five-pole filter is also fabricated with centre-frequency tunability of 14% from 1.764 to 2.015 GHz and 15 dB bandwidth tunability of 107% from 41 to 85 MHz. Midband insertion loss is kept below 1.4 dB in all tuning states. The five-pole filter is compared to other tunable filters in the UHF range and is shown to reduce midband insertion loss by 36% from the next best filter (2.2-1.4 dB). [ABSTRACT FROM AUTHOR]