Theoretical and experimental analysis of microwave tunable recursive active filters using power dividers

It is shown how power dividers can be effectively employed in the design of microwave recursive filters in strict accordance with low-frequency principles. Analytical, computer-simulated, and experimental results are presented for an active recursive bandpass filter, and for a newly developed tunable recursive active filter employing a reflection-type microwave phase shifter and implemented on a Duroid substrate in the 2.75-3.75-GHz range. The last step in the filter design was to insert a classical reflection-type analog phase shifter structure directly into the recursive loop, to help in the realization of a tunable recursive response. Measured S-parameters of the circuits show excellent agreement with theoretical analysis.<>