A Generalized Radiometer System Equation That Includes Temperature-Dependent System Losses

This paper presents a generalized radiometer system equation (RSE) for total power radiometers that corrects for mismatch and temperature-dependent system losses, and may be applied with any combination of calibration sources. The equation is validated through simulation in Keysight ADS as well as experimentally using a K-band radiometer. The estimated temperature is compared with calculated values from other known equations, which are reduced forms of the RSE under different assumptions, namely (i) all components are at the same temperature (isothermal case), and (ii) mismatch can be ignored and only temperature-dependent insertion loss is corrected (loss only case). Simulations with a 50 Ω load at 310 K shows errors of −0.18 K, −0.56 K and −0.76 K with the RSE, isothermal case and loss only case, respectively. Experimental results confirm that the RSE gives the lowest error, thereby demonstrating that it models the system more accurately than the other two treatments.