This document describes a band notched microstrip-fed monopole antenna designed for ultra-wideband applications. The antenna consists of a square radiating patch with two L-shaped slits and an inverted T-shaped notch in the ground plane. Simulation results show that the antenna provides a wide fractional bandwidth of over 140% between 1.4-12.4 GHz, with a single notched band between 3-5 GHz. The antenna has a compact size of 16x10mm and omnidirectional radiation patterns in the E-plane. The L-shaped slits in the patch and inverted T-shaped notch in the ground plane help generate the band-notch characteristics while maintaining a wide impedance bandwidth.