Tunerless millimeter wave ring filter for wide temperature range

Awaveguide ring filter design for the 119 GHz heterodyne receiver of the Odin satellite is reported. The relatively narrow band filter is designed to operate without external tuners although the ambient temperature can vary from 100 K to 300 K. The critical temperature related changes in the center frequency of 114.85 GHz are compensated by the mechanical design with use of suitable materials. A maximum frequency shift of 440 MHz was reduced to 80 MHz in the first prototype, with further improvements to be expected in later models.