Probe-fed strip-element microstrip phased arrays: E- and H-plane scan resonances and broadbanding guidelines

A comprehensive investigation is presented of E- and H-plane scan-frequency characteristics of probe-fed microstrip strip-element phased arrays with a single probe per unit cell. A parametric study of the principal, large mismatch producing scan resonances is carried out utilizing Galerkin-type analysis and an associated computer code. While the E-plane scan characteristics confirm earlier findings, those of the H-plane exhibit a heretofore not reported array blindness condition which is traced to excitation of a strip-line mode of the periodic array structure. The largest element spacing is identified which, independently of substrate thickness, excludes the principal E- and H-plane scan resonances. Element broadbanding is then achieved via interplay between substrate thickness and strip width. For a fixed scan angle with an appropriately configured element geometry, the unmatched active impedance exhibits a double-tuned behavior. The form of the equivalent network in the neighborhood of the double-tuned resonance is established via computer-aided approach. Finally, an example of scan-frequency array performance (without using suppressor pins) for a /spl plusmn/15% frequency range and a 40-degree E- and H-plane scan coverage with voltage standing wave ratio (VSWR) /spl les/2 is presented.<
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