Optical beamforming network for controlling an RF phased array

Details Optical beamforming network for controlling an RF phased array Optical beamforming network for controlling an RF phased array

1989-08-01

1990-10-23

Issing, Gregory C.

Communications: directive radio wave systems and devices (e.g.,

Directive

Including a steerable array

356349, 350 368, H01Q 322, G01B 902, G02B 112

Patent

active

049656031

ABSTRACT:
An optical beamforming network is provided for controlling the RF radiation pattern of a phased array antenna. Light from a first laser is modulated by a spatial light modulator that is user-programmed with the desired far field radiation footprint. The modulated light beam is directed through a Fourier transform lens and onto a beam splitter where it is combined with light from a second laser that is frequency offset by the RF center frequency of the antenna. Light from the beam splitter is recovered by first and second fiber optic bundles. Each optical fiber leads to a corresponding photodetector that detects the beat frequency produced by the two frequency offset light beams. The outputs of corresponding photodetectors of the two fiber optic bundles are combined to control the radiation of a corresponding radiation element of the phased array. The use of two sets of optical fibers and photodetectors improves the signal-to-noise ratio of the system. An alternative embodiment of the invention uses photorefractive crystals to pass phase conjugate return beams back through the optical lenses to cancel lens-induced aberrations from the spatially modulated light beam. This embodiment reduces distortion of the far field radiation pattern without the use of high quality optical lenses.

REFERENCES:
patent: 4280764 (1981-07-01), Sica, Jr. et al.
patent: 4718749 (1988-01-01), Chiou et al.
Koepf. Optical Processor for Phased Array Antenna Beam Formation, SPIE vol. 477, Optical Tech, for Microwave Applications, 1984.
Koepf, G. A., "Optical Processor for Phased-Array Antenna Beam Formation", SPIE vol. 477, 75-81 (1984).

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