Electronically tunable microstrip combline filter

The authors present the design of a fast, electronically tunable microstrip combline filter. Packaged GaAs tuning diodes are employed as the tuning elements. The design incorporates the results of experimental varactor characterization. Thus, the package and mounting parasitic effects are adequately estimated. Tapped line input and output matching circuits are proposed to compensate for the effect of frequency-dependent coupling between the filter resonator elements. Measured results for a filter designed using the proposed method show close agreement with those predicted by computer simulation.