Hourglass Slot Antenna with Exponential Flare for Wideband and Direct Coaxial Cable Feed

This paper presents a compact Ku-band slot antenna featuring an hourglass-shaped aperture enhanced by an exponential flare, designed for wideband millimeter-wave radar applications. The proposed antenna achieves an impedance bandwidth from 12 GHz to 18 GHz, enabled by the gradual flare profile inspired by Vivaldi antennas. A key advantage of the design is its compatibility with direct feeding using a $\mathbf{5 0 - o h m}$ semi-rigid coaxial cable, which simplifies fabrication and integration without requiring a matching network. Simulation results demonstrate a directional gain of approximately 6.7 dBi with a broad beamwidth and minimal sidelobe levels. The proposed antenna is well-suited for compact radar systems that require wideband performance and simplified feed architecture.