A photonic in-phase/quadrature (I-Q) rf phase shifter utilizing the signals from two integrated optic Mach-Zehnder modulators has been tested. This system demonstrates the capability of 360-deg phase control, less than 1-deg rf errors at constant amplitude, and less than 0.5-deg errors over a 30-dB rf amplitude taper. Using this technique, a four-channel beam-forming network was also developed and integrated with a printed patch, lightweight phased array antenna. High-accuracy linear beam control was achieved. Null patterns of more than 30 dB were produced on boresight. The null was steered to greater than 30 deg from boresight with a linear accuracy of approximately 1 deg.