Precision combiner networks for phased array antennas

Abstract

Low sidelobe phased array antennas require precise control of the amplitude and phase illumination functions.A recent design uses a nearly circular aperture w i t h 4350 radiating elements arranged combiner networks used t o form the elevation sum and elevation i n 79 columns and 139 rows. This paper describes the column difference signals for each of the 79 columns. Since the array has centerline synnnetry, 40 different designs are needed. Using the smallest has 8 i n p u t s .two-element subarrays, the largest combiner has 36 inputs whileThe combiner networks are essentially multiple interferometers where signals from two-element subarrays equidistant from the array c e n t e r l i n e a r e combined i n three branch hybrid junctions to form partial sum and difference signals. The p a r t i a l sum signals and p a r t i a l d i f f e r e n c e s i g n a l s a r e then separate1 combined w i t h ladder networks of weighted split-tee power dividers T . A schematic of a typical combiner network is shown i n Figure 1. The s t r i p l i n e c i r c u i t f o r each combiner, consisting of up t o 17 one-ounce copper on a 0.004-inch thick Teflon/glass substrate. hybrid junctions and 34 s p l i t -t e e power combiners, is etched from The e t c h e d c i r c u i t which may be as large as 47-inch by 17-inch is a 0.064-inch layer of polyimide/aramid fiber honeycomb between t h e supported between two t h i n aluminum ground planes by interposing c i r c u i t and each ground plane. The s t r i p l i n e assembly, w i t h a ground plane spacing of 0.132-inch, is bonded t o g e t h e r t o form a semi-rigid light-weight device. A dimensioned cross-section is shown i n Figure 2. Physical constraints of the array package require t h a t r i g h t angle surface-launch connectors be used a t a l l o f t h e combiner ports. maintain the quasi-TEM integrity of the device. These Self-jigging metallic inserts are used a t each launcher to maintain dimensional tolerances during the bonding operation a t inserts, together w i t h a metallic edging, provide hard points to elevated temperature and pressure. Design o f t h e s p l i t -t e e power dividers was complicated by the requirements that the resistor handle several kilowatts of peak phase be nearly equal for the two ports and nearly equal for all power and several watts of average power, and t h a t the transmission of the coupling values. The r e s i s t o r is a thick-film deposited on a specially shaped beryllia body. Capacitance associated w i t h the r e s i s t o r was compensated by the addition of two open-circuited stubs and by adjusting the dimensions of the matching transformers.