Ka-band slot-fed higher order-mode low-loss Fabry-Perot filters

Low-loss bandpass filters consisting of Fabry-Perot resonators excited by slots which couple to higher order resonator modes are demonstrated. For close reflector spacings, the slots efficiently couple power from rectangular waveguide to the TEM/sub 400/ and TEM/sub 300/ modes of the resonator. At Ka-band the filters have insertion losses less than 1 dB in general and less than 0.5 dB in some cases. The unloaded Q values of the filters range from 1500 to 3000. The filters are mechanically tunable over a 25% bandwidth.<
>