Abstract
This letter presents a dual-polarization inverted quad-ridged flared horn antenna with an extremely wideband of more than one decade in the range of 2–20 GHz. The modes of the inverted quad-ridged waveguide are analyzed first. A cross-shaped inverted ridge, with low TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode cutoff frequency and a tip significantly higher than the horn aperture, is proposed. The inner surface of the horn wall is based on a composite curve flare rate. It is optimized to cooperate with the inverted ridge. Furthermore, the polytetrafluoroethylene back cavity replaces metal back cavity to suppress the high- order mode in the back cavity. The measured isolation between the two orthogonal linearly-polarized ports is nearly 45 dB and the reflection coefficient is less than –15 dB over the entire working frequency band.
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