Error analysis of an analog correlator for polarimetry

In this letter, we consider a performance evaluation of an analog correlator, and extract Stokes parameters from cross correlation between horizontal and vertical channels of electric fields for a fully polarimetric radiometer. To this end, we develop an analog correlator using 90 degrees and 180 degrees hybrid couplers and square-law detectors. In order for its performance analysis, we derive a closed form of a mathematical representation for Stokes parameters in terms of amplitude and phase responses of both channels, characteristics of hybrid couplers. As a result, the cross correlation of U and V of Stokes parameters is 0.92 and 0.96, respectively. And the maximum return loss of the proposed analog correlator is less than -23 dB for all directions. In addition, the peak-to-peak amplitude response of the proposed analog correlator is 1.9 dB, and for the phase response as 9 degrees. We compare numerical and measured results of I and U of Stokes parameters, and obtain their average errors as 0.4% and 14.9%.