Increased Bandwidth Evanescent Open-Ended Waveguide Antenna Design Using the Imaginary Smith Chart

We present a novel antenna matching technique that uses the Imaginary Smith Chart to permit wideband matching of an evanescent open-ended waveguide antenna using a dielectric sheet air-spaced from the aperture. The fabricated antenna design is demonstrated to have a measured bandwidth of 24%, from 2.13–2.7 GHz, for reflection coefficient
$\qquad{<} -\!\!10~{\rm dB}$
, with 2.725 GHz waveguide cutoff. The antenna's maximum aperture dimension is
${< 0.5}\lambda_{0}$
at the upper frequency in the bandwidth and so it is suitable for use in a wide angle scanning phased array.