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

An ultrawideband H-plane horn antenna excited by a modified double-sleeve monopole is proposed in this letter. Two sets of circularly arranged metallic posts around the feeding probe are employed to form a double-sleeve structure for bandwidth enhancement purposes. 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, a corrugated surface is designed at the horn aperture to improve the E-field distribution at high frequencies and achieve a better front-to-back ratio. The proposed antenna demonstrates nearly endfire radiation within the entire frequency band from 2.08 GHz to 9.3 GHz with |
S
11| < −10 dB, indicating that an ultrawideband of 126.8% is obtained. The proposed structure features a compact size of 0.52 × 0.83 × 0.17
λ_L
³
, corresponding to the lowest operating frequency, which is promising for platform-mounted applications.