Importance

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Abstract

A dichroic antenna scanner is comprised of transmission or reflection surfaces that impart to an incoming wave a phase shift which varies across the surface of the antenna. For this purpose, a multilayer dichroic structure may be configured to have a controlled tapered spacing between the various layers or a variable reflectance across the dichroic surface, thereby varying the cut-off frequency of the dichroic surface across its surface. Since the phase of a transmitted or reflected wave varies rapidly in the vicinity of the cut-off frequency, a variation in the cut-off frequency across the dichroic surface yields a varying phase characteristic across the antenna. Because the phase shift characteristic of the dichroic is frequency-dependent and varies sharply in the vicinity of the cut-off frequency, an incoming wave, the frequency of which is far from cut-off, will not be as greatly affected as one near cut-off, so that selection of effectively scanned and nonscanned frequencies is possible merely by adjusting the insertion loss characteristic of the multilayer dichroic structure. Selective scanning of different frequencies may be accomplished by rotating the dichroic surface structure.

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First Claim