ELECTRONICALLY STEERABLE SPHERICAL ARRAY CAPABILITIES AND INTERFACES

Abstract

For antenna applications which require gains of 7 to 23 dBic over very large solid angle coverage regions, the Electronically Steerable Spherical Array (ESSA) is an antenna which has significant benefits. This paper describes these benefits along with the ESSA’s key performance parameters and its electrical and mechanical interfaces. As extensions of the basic ESSA design, this paper also describes alternate configurations which allow multiple beam operation and integrated packaging of RF electronics. Basically a simple antenna, the ESSA forms its beams by selecting N elements which point in the desired direction. Selection of these elements is performed by a multipole PIN diode switch. This switch sums together the N desired elements from the M elements located on the ESSA’s spherical surface upon receipt of the appropriate commands from the ESSA’s dedicated microprocessor. The ESSA may be either Phase Compensated, or Non-Phase Compensated. In the Phase Compensated ESSA, a 1 or 2 bit phase shifter is used to correct the spherical phase front produced by the array shape. That correction results in higher gain. The most important ESSA benefits are its characteristics of constant phase and gain which are independent of beam pointing angle. These characteristics free the system from the gain and phase perturbations caused by other types of antennas. As a mature technology, the ESSA has been successfully tested with the NASA standard transponder and is presently being fabricated as a 14 dBic gain protoflight unit for a NASA-Goddard Space Flight Center program.