Compact Ultra-Wideband H-Plane Horn Antenna Inspired by Modified Double-Sleeve Monopole

An ultra-wideband H-plane horn antenna excited by modified double-sleeve monopole is proposed in this paper. Two sets of circularly arranged metallic posts around the feeding probe are employed to form a double-sleeve structure for the bandwidth enhancement purpose. Three pairs of posts are utilized in the waveguide to achieve the higher-order modes suppression and impedance matching improvement. A tapered horn aperture is mainly employed to smoothen the transition between the waveguide and free space for improving the impedance matching. Additionally, corrugated surface is designed at the horn aperture to improve the E-field distribution at high frequencies and achieve better front-to-back ratio. The proposed antenna demonstrates nearly end-fire radiation within the entire frequency band from 2.08 to 9.3 GHz with |S11| < -10 dB, indicating that an ultra-wideband of 126.8% is obtained. The proposed structure features a compact size of 0.52×0.83×0.17•L3 corresponding to the lowest operating frequency, which is promising for platform-mounted applications.