Varactor-Tuned Dual-Mode Bandpass Filter With Nonuniform $Q$ Distribution

This letter demonstrates an electronically reconfigurable microstrip dual-mode filter with nonuniform Q lossy technique. Varactors are used for continuous tuning of the bandwidth and center frequency. By deploying nonuniform Q distribution on the dual-mode open-loop filter, passband flatness is improved by loading resistors on the even-odd symmetrical plane of resonators. Coupling matrix is used to describe the tunable lossy filter. Design of this type of four-pole tunable lossy filter is presented and validated experimentally.