PIN millimeter-wave switching diodes were developed for operation in a two phase path-length modulator, over the frequency range 40-110 GHz. The paper investigates the effect of diode stored charge and switching speed on modulator output. The 300 Mb/s switching performance of 40 to 110 GHz PIN diodes is presented as a function of their storage and fall time, which varies from 2 to 18 and 0. 2 to 1. 2 ns, respectively. The text of this paper is in digest form.