Design of an Electronically Tunable Microstrip Bandpass UHF Filter

This paper presents the study results of tunable microstrip bandpass filters (BPF) in the decimeter range for various structure types (stepped impedance, combline, and open-loop). The considering central frequency is tuned by using varactors in the range of 1.8 - 2.5 GHz with a 200 MHz bandwidth. The investigated filters are based on hybrid technology using standard commercially available electronic components for surface mounting. The comparative characteristics of the various microstrip tunable filters are presented. The data obtained can allow a rational choice of design for the device to be developed.