An estimate of the levels of the individual components of the spectrum of a single-sideband modulator

Abstract

The error in measuring the spectral characteristics of mechanical polarization modulators are mainly due to such parasitic components as the residue of the carrier and the mirror sideband [1]; other parasitic components have a higher order of smallness. One of the drawbacks of mechanical polarization modulators is the low modulation frequency (of the order of 100-200 Hz), which considerably complicates the measurement of the carrier residue and the mirror sideband and the processing of the mechanical polarization modulator. Below, using the example of the analysis of the two-channel circuit of a microwave phasemeter with a single sideband modulator in each channel [2], we consider a simple method of estimating the levels of the carrier residue and the mirror sideband, and we determine the extent to which they affect the measurement error. The modulated signals, containing information on the phase shift, are summed and converted using a square-law detector. The intermediate-frequency voltage to be measured is separated out by filters from the low-frequency voltages obtained. For single-channel modulation the intermediate frequency is equal to the frequency of the modulating function, while for two-channel modulation it is equal to the sum or difference of the two frequencies.