Photonic True Time Delay Beamformer for a 20 Element L-Band Phased Array

摘要

A phased array is a directive antenna made up of individual radiating elementswhich generate a radiation pattern whose shape and direction are determined by the relative phases and amplitudes of the currents at the individual elements. Current state of the art phased array radars implement electronic phase shifters for beamforming. The limitation of the phase shifters becomes apparent if multiple frequencies are transmitted simultaneously. The energy associated with the different frequencies will point in different directions in the antenna's far field causing an increase in beamwidth. This phenomena, called squint, restricts the phase shift approach to narrowband operation. A trne time delay line based on an optical heterodyning technique is used to generate properly phased signals enabling wide bandwidth operation. The theory, design, development, testing and analysis for photonically controlling a 20 element, wide bandwidth (200 MHz) L Band phased array radar are presented.