Design and measurement of a WR-28 calorimeter

We have designed and manufactured a new WR-28 (26.5–40GHz) rectangular waveguide calorimeter. The former WR-28 calorimeter was setup during 1980s, many parts are not work, and especially the mount is not available. So the new calorimeter needed. 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. 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.