Abstract: A lightweight microwave filter device is disclosed which utilizes a housing made of a lightweight metal such as aluminum having a relatively large coefficient of thermal expansion. The microwave filter also utilizes resonator elements which are either interdigital or in a comb-line filter arrangement. The resonator rods are made in two segments -- a lightweight metal such as aluminum having a relatively large coefficient of thermal expansion and a metal having a very low coefficient of thermal expansion such as invar. As the temperature varies the length of the rod also varies. The tuning capacitance between the rods and the housing varies with temperature changes and compensates for the change in the rod length. Thus the resonant frequency of the microwave filter is maintained relatively constant over a predetermined temperature range.

Abstract: A microwave tuning device is disclosed which utilizes a resonator rod mounted in a housing. One end of the resonator rod is attached, or shorted, to the housing wall and the other end is unattached or open. The open end of the resonator rod has a cylindrical recess and an insulator ring is disposed between the open end of the resonator rod and the cavity wall. A tuning screw is incrementally inserted through the insulator ring and into the cylindrical recess for adjusting the tuning capacitance and thereby the resonant frequency.