Methods for measuring the power linearity of microwave detectors for radiometric applications

Abstract

This paper discusses and presents experimental results on methods for measuring the power linearity of microwave power detectors to the levels required for radiometric applications. Three methods for measuring detector power linearity are discussed: the two-tone method, the amplitude modulation method, and the constant ratio method. The theory of determining coefficients which characterize the nonlinearity of the detector from experimental data is presented. Experimental results are presented showing that the twotone method and the constant ratio method agree within experimental error. The difficulties encountered in implementing each of these methods are also discussed.

Analysis of nonlinear effects in microwave spectrometers

“…In order to precisely measure the brightness temperature of an atmospheric gas, a microwave radiometer relies on the power linearity of microwave components which compose the heterodyne system [ Reinhardt et al , 1995; Murk et al , 2005]. Nevertheless, the accuracy of these devices could be affected by nonlinear behavior.…”

“…Some other approaches involving other kinds of mathematical models are used to describe amplitude and phase nonlinearities. On the basis of these, comparison with experimental results by different methods such as single‐tone, two‐tone, three‐tone and noise loading tests have been performed by Heiter [1973], Reinhardt et al [1995], and Berceli and Marozsák [2006]. In related fields, other measurements which address the importance of accuracy in microwave systems, such as attenuation standards [see Widarta et al , 2003; Iida et al , 2006] or microwave devices [see Holland and Howes , 2002], have also been developed.…”

The WindSat spaceborne polarimetric microwave radiometer: sensor description and early orbit performance

“…Following the suggestion of Hoer et al [16], we optimized the linearity of the diode detectors by adjusting the load resistance, again in pairs so that performance could be matched. The linearity of the receivers was tested using the two-tone method [17] over the thermal operating range. Nonlinearity was measured to be less than 0.1% and typically 0.06%.…”

APMIR: an airborne polarimeter designed for high accuracy

“…The choice of the optimal resistance values arose from the results of a two-tone test [3] performed on the detectors. The detectors for signals that were to be combined in post processing were also matched with each other according to the results of the two-tone test.…”