Design and measurement of a WR-42 calorimeter

Three calorimeters are being developed as national primary power standards which cover frequency range is 18-26.5 GHz, 26.5-40 GHz and 40-60 GHz. The connectors are WR-42, WR28 and WR19. At present, WR-42 calorimeter has been assembled and some measurements done. The calorimeter is designed as twin line structure and put in two layers copper barrel. The outer one is temperature controlled to reduce the effect of the change of ambient temperature. The temperature wave in inner barrel is less than 50 micro degrees within 24 hours. In this calorimeter, general used microwave load be used as the terminator, other than special designed mount. Resistor heater is tightly tied to load which can provide DC bias power. A commercial bolometric sensor embedded into a hole in the waveguide flange with a type IV power meter is used to detect the DC substitution power. The design and measurement results of the WR-42 calorimeter are presented.