A true time delay phased array is provided which includes a digital subarray interface in the transmit signal path. The digital transmit signal path interface includes a digital reference signal generation means and digital signal propagation means for supplying the digital reference signal to the subarray. Each subarray includes RF carrier signal generating means for generating an RF carrier signal phase coherent with the reference signal, a fiber optic true time delay circuit for applying an appropriate phase delay to the RF carrier and an appropriate true time delay to the modulation signal, and a waveform modulator for modulating the modulating signal onto the phase locked RF carrier signal to provide the transmit signal for the subarray. The present invention can be used in conjunction with existing digital interface technology for receive and control signal paths to provide an entirely digital subarray signal path interface.