Elimination of even-order modulation in rectifier modulators

Previous analytical treatments of rectifier modulator circuits have usually assumed that the time-varying-resistance function of the rectifiers is a square wave. Differences in behaviour when the function is not only not square, but also contains even-order harmonics of the carrier frequency, are here discussed. Among other and more general results, it is shown how even-order modulation products can be eliminated altogether in the ring, series and shunt types of modulator provided that (a) the carrier waveform comprises only odd harmonics and (b) the external circuit impedance is a pure resistance R at all odd-order modulation-product frequencies, and can be related to the rectifier resistance/ voltage characteristic, r(Vc), so that R2 = r(+Vc).r(¿Vc). This condition coincides with that for minimum conversion loss.