Tunable Filters

High performance RF tunable filters are needed in reconfigurable systems to facilitate efficient utilization of the available frequency spectrum. Tunable filters are also used to replace large filter banks in advanced systems concepts that self‐adapt to environmental requirements. This chapter focuses on high‐Q tunable three‐dimensional (3D) filters such as combline, dielectric resonator, and waveguide filters with Q values that can meet the stringent performance requirements of wireless base station and satellite applications. It addresses filters that are tunable in both center frequency and bandwidth. The ideal tunable filter must exhibit the following features: high loaded Q value, wide tuningrange, high tuning speed, good linearity, high power handling capability, small size and mass,and high reliability. In order to minimize the number of tuning elements and to improve the loss performance of the tunable filter, it is preferable to use tuning elements only to tune the resonator center frequencies.