Spatial-spectrum estimation and filtering of radio frequency arrays via elemental photonic up-conversion and coherent optical processing

Abstract

A method for imaging Radio-frequency (RF) side-bands about an optical carrier signal, previously devised for passive, non-coherent, imaging of millimeter wave radiation is furthered for use in coherent reception of Radio-frequency signals. Theoretical formulation of a novel photonic beam-space beam-former is presented along with relationships to traditional beam-space array theory. The photonic beam-forming system requires each element of a Radio-Frequency (RF) array be optically up-converted to a laser carrier frequency and fed through a photonic processing system, where the output beam-space is sampled using an array of photo-detectors (or a commercial camera). Specic contributions of this work allow for a more power ecient optical system, amplitude calibration of the optical chain, arbitrary apodization (or tapering) of the output beam-space and application of the receiver system to multiple simultaneous domains (e.g. active sensing and communications in one receive array). Furthermore, a novel adaptive weighting approach is presented that utilizes outputs from both a commercial camera device and an array of high-speed photo-detectors to enable array adaptivity that is shown to be of low-latency when compared to existing techniques. Several experiments are performed using prototype hardware to characterize the system, component and algorithm-level performance enabling more capable designs within future work.