Group Delay-Based Wideband Photonic Receive-Mode Radio-Frequency Beamforming

A multi-channel wideband group delay-based photonic receive-mode beamformer implemented with bulk fiber-based true-time delays, discrete flat-top arrayed waveguide gratings (AWGs), and a linear receive antenna array is presented. The frequency-independent beam pointing angle is derived theoretically, along with the multi-channel RF gain and noise figure. Dependence of RF gain and noise figure on channel count is investigated experimentally and shown to agree with theoretical prediction. Flat-top and Gaussian AWG optical filter transmission and bandwidth are measured and their effects on RF gain and phase are compared. Effects of channel-to-channel RF amplitude and phase mismatch on the RF response are shown by comparison of measurement with theory. Finally, measured beamformer antenna patterns are provided to demonstrate the formation of four simultaneous beams.