Wideband polarisation diverse phased arrays

Design approaches for realising an octave band, ±60° angle scanning, polarisation diverse phased array with high polarisation purity are investigated. The realisation of such an array as a low profile flat plate structure is also a requirement. Straightforward approaches using loaded waveguide elements such as dielectric filled circular or square waveguides or quad ridged structures, even with ridges protruding from the waveguide, exhibit unacceptable limitations in terms of: wideband impedance matching, realised element beamwidth and polarisation purity degradation associated with unequal E and H-plane mutual coupling. A unique approach using square evanescent mode waveguide cavities excited by printed probes near the aperture, augmented by aperture irises and a WAIM (wide angle impedance matching) sheet (high-K thin dielectric) spaced approximately λ &ogr;/8 from the aperture, potentially can overcome the limitations cited above