A Combline Tunable Filter with Loss Compensation Circuit

This paper presents an implementation of a tunable combline filter using varactors with active loss compensation. The use of varactors results in a compact implementation with fast and continuous tuning. The active loss compensation mechanism helps to compensate for losses generated by the tuning elements. Nonlinear performance and power handling of the tuning circuits are characterized. The filter operates at 2.5GHz with a constant absolute bandwidth of 25±3MHz. Measurement results demonstrate a tuning range of 100 MHz while the insertion loss remains below 0.9dB over the tuning range.