D. Thomas

Multiple beam synthesis of low sidelobe patterns in lens fed arrays

Low sidelobes in lens fed multibeam arrays present some unique problems. The technique of synthesizing low sidelobe patterns by the superposition of multiple orthogonal beams offers several advantages, particularly in lens fed arrays. It is shown that the Taylor line-source distribution is a superposition of multiple orthogonal beams. It is further shown that use of only three beams provides patterns close to the exact Taylor pattern for theoretical sidelobe levels as low as -43 dB. In an experimental implementation of the technique, sidelobe levels of -29.9 dB have been measured using three central beamports in a lens fed multibeam array. Over a 10-percent band, -28 dB levels were maintained. Trimming array cables to eliminate random phase errors lowered the sidelobe levels to -32.6 dB over a narrow band.

Design of multiple-edge blinders for large horn reflector antennas

Attaching blinders to the sides of pyramidal horn reflector antennas and other large aperture antennas is one method of controlling high sidelobes for horizontal polarization. This paper describes analysis and design procedures for arriving at a useful multiple-edge blinder for reducing undesirable sidelobes of a pyramidal horn reflector antenna. Several blinders have been designed and tested for use with a pyramidal horn reflector antenna. They are directed at reducing a high sidelobe near 90\deg in the azimuth plane where levels (referred to the main lobe) of -52 dB at 3.74 GHz and -58 dB at 6.325 GHz are presently typical. A 14-edge blinder designed using these techniques reduced these levels by 20 dB at 3.74 GHz and 12 dB at 6.325 GHz and did not significantly degrade antenna performance for other angles and other polarizations.

Selection of Phased Array Configuration

A major decision in the design of phased array antennas is the selection of array configuration. Once the coverage sector, net antenna gain, effective radiated power (ERP) and other system requirements are established, the effects of (1) subdividing the coverage sector, i. e. , using multiple antennas and (2) choosing linear versus sector arc arrays can be determined.