Temperature dependence of the conversion loss and response time of InSb mixers

The performance of bulk InSb mixers is investigated, A heterodyne experiment has been performed at 69 GHz with IF's varying from 0.4 to 20 MHz. In this experiment the conversion loss was measured as a function of the intermediate frequency (IF) for ambient temperatures in the range 1.5 to 20°K. The IF at which the conversion loss increased by 3 dB determined the response time. Using an electron temperature model, expressions for the conversion loss and the response time are derived by making a small-signal expansion of an energy balance equation. Good agreement between theory and experiment is shown. In this theory the InSb mixer is viewed as a bolometer mixer. An evaluation of mixer performance, stressing operation at ambient temperatures in the 1.5 to 20°K range, is presented. The available tradeoffs between conversion loss and response time as a function of ambient temperature and applied fields are given. Values as low as 11 dB for the minimum conversion loss can be obtained at 1.5°K, where the maximum useable IF is 1 MHz. To obtain a substantially higher IF, such as 10 MHz, the temperature must be increased to 16°K. However, the optimum conversion loss increases at a rate of 1 dB/°K and is 27 dB at 16°K. It is also shown that the device performance of InSb mixers can be predicted satisfactorily from static I-V characteristics and that the best mixer material can be determined by making simple dc measurements.