Techniques for optical simulation of antenna radiation patterns

Advances in techniques for optical simulation of microwave antennas have been made over the past year since the initial announcement of the technique by A. L. Ingalls at the 1964 PTGAP Symposium. In optical simulation, an optical aperture is illuminated by the spatially coherent modes of a gas laser to simulate the aperture distribution of a microwave antenna. The resulting optical diffraction pattern then simulates the pattern of the microwave antenna. New techniques are being developed at Wheeler Laboratories and include the recognition of the validity of the concept of simulation, where, for example, microwave apertures of the order of 100 wavelength size are simulated with optical apertures of the order of 10,000 wavelength size. Another new technique is the straightforward engineering development of automatic recording of optical diffraction fields. Precision of measurement has been obtained which is comparable to or better than that obtained at microwave frequencies. A third advance in technique is that of simulating the difference-mode of monopulse tracking antennas with the TEM-10 mode output of gas lasers.