A Wide-Band Phase-Feedback Inverse-Sine Phase Modulator with Application Toward a LINC Amplifier

A wide-band inverse-sine phase modulator is demonstrated. The modulator has application in a LINC amplifier for linear amplification at microwave frequencies using commonly available saturating amplifiers or injection-locked oscillators. A bandwidth greater than 10 MHz at a carrier frequency of 96 MHz with distortion products 40 dB or greater below desired components has been shown. The distortion behavior as a second-order effect of the loop delay as predicted by analysis has been verified. The output of the inverse-sine phase modulator and its conjugate, generated by a second phase modulator, were subtracted as in a LINC amplifier, to provide at least 40-dB suppression of the zeroth order and even-order components.