A compact slot antenna for high-gain ultra wideband applications is presented. The slot is asymmetrically cut in the ground plane and is a combination of two rectangles. A hexagonal patch with two stepped coplanar waveguide-feed is used to excite the slot. The capacitive reactance of the hexagonal patch is neutralized by the inductive reactance created by the asymmetric slot and results into wider impedance matching. The measured impedance bandwidth of the proposed antenna is 11.85 GHz (2.9–14.75 GHz). The radiation patterns of the proposed antenna are found to be omni-directional in the H-plane and bi-directional in the E-plane. To enhance the gain of the antenna, a compact three-layer frequency selective surface (FSS) is used as a reflector. The overall thickness of the FSS is 3.5 mm. There is 4–5 dBi improvement in antenna gain after application of the FSS. The measured and simulated results are in good agreement.