Beamforming for Phased Array Antennas by Optical Means

Phased array beamforming requires the adjustment of both amplitude taper (primarily for side-lobe level control) and phase taper (for main beam coverage control) across a given antenna aperture. Such tapering is generally implemented by employing phase shifters and attenuators (or amplifiers) behind the individual radiating elements. Recently developed photosensitive microwave PIN diodes have opened up the possibility of realizing such circuits which can be controlled by optical rather than by electrical means. The implications of optical signalling (by fiberoptics) include reduced weight (as compared to copper conductors) and immunity from EMI/EMP effects, both of which are priority items in air- and spaceborne applications. The new microwave PIN diodes are applied in the analysis and design of beamform control circuits for phased array antennas. The diodes are characterized and applied in the design of an optically controlled reflective phase shifter.