In this paper, a high-gain band-notch crown-shaped ultra-wideband (UWB) monopole antenna is proposed and investigated. A modified U-shaped slot is etched from the radiator to eliminate the WLAN band (4.7–5.9 GHz). Further, frequency-selective surface (FSS) of 5 × 5 array is designed and placed below the antenna to increase its gain. The novelty of the proposed FSS is, it enhanced the antenna gain throughout the operating frequency range except the rejection band (5.15–5.85 GHz). The measurement results show that after embedding FSS array, the antenna gain is increased from 3.5 to 9 dBi at 8.5 GHz, without affecting the rejection band. In addition, front-to-back ratio (FBR) is also improved from 5 to 23 dB at 9 GHz. Further, the proposed antenna offers an impedance bandwidth of 93.3% from 3.5 to 11.2 GHz. An electrical equivalent circuit of a unit FSS cell and antenna is also realized to verify the simulation results. Mode analysis is also performed, and it is observed that the antenna is configured to utilize the TM22 mode at 4 GHz and TM11 mode at 8 GHz.