Design Criteria and Numerical Simulation of an Antenna System for One Dimensional Limited Scan
AIR FORCE CAMBRIDGE RESEARCH LABS HANSCOM AFB MA
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An analytical and numerical study was performed on a novel design scheme for an antenna for limited one-dimensional scan. The system has a number of control elements approximately equal to the minimum that are theoretically compatible with the aperture size and field of view FOV. The radiating structure consists of a boot lace lens with linear outer and circular inner profiles. This geometry plays a basic role in determining excellent scan performance over a moderate frequency band. A linear array whose size depends critically upon scan requirements and the lens focal length is located on the focal plane and is focussed onto the inner lens profile. The array is fed by a Hybrid Network HN performing a spatial Fourier transformation. The input ports of the HN are fed by the output ports of a Beam Forming Network BFN through a set of variable phase shifters. The BFN has separate input ports for the sum and difference patterns controlled independently. The system works as follows. The antenna illumination is synthesized as the weighted superposition of components illuminations or overlapping subarrays, each of which is due to the excitation of one of the ports of the HN. The amplitudes of the subarray excitations are fixed and determined by the power divisions provided by the BFN. Their phases are controlled by the set of variable phase shifters. A desirable feature of the scheme is that for fixed phase shifter settings, neither the beam scans nor the width changes for a moderate frequency variation.
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