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In this paper, the generation of an arbitrary band-limited phase-modulated RF signal from a pulse-position-modulated (PPM) optical pulse train is investigated. We show that a specifically designed PPM pulse train would have a multichannel spectral response, with one channel having the spectrum corresponding to a phase-modulated RF signal. By using a microwave bandpass filter to select the channel of interest, a phase-modulated RF signal is obtained. The relationship between the pulse position modulation and the phase modulation is derived and analyzed. Two design examples are presented, with one for the generation of a chirped RF signal, and the other for the generation of a binary phase-coded RF signal. The chirped pulse has a central frequency of 50 GHz and a 3-dB bandwidth of 12.5 GHz. The binary phase-coded RF pulse has 15 chips with a central frequency of 5.34 GHz. The proposed approach provides a simple and effective solution for the generation of high-speed arbitrary phase-modulated RF waveforms for applications in modern radar, communications, and imaging systems.