This article describes multiresonance behaviour to achieve ultra-wideband (UWB) characteristics of a co-planar waveguide (CPW) fed circular patch antenna with a ground plane reflector by using fractal elements and rectangular defective ground structure (RDGS) technique. The patch consists of a circular disc with six ring type fractal elements on the periphery of the disc and slotted defective ground surface (DGS) at the bottom of an FR4 epoxy dielectric substrate to increase the antenna bandwidth. The antenna resonates at frequencies of 5.4 GHz, 9 GHz, & 10.8 GHz with return loss better than −20 dB. The proposed antenna also exhibits UWB characteristics with (≤ −10 dB) impedance bandwidth of 170.4% in the frequency range from 1.8 GHz to 11 GHz. This covers the whole UWB range from 3.1 GHz to 10.6 GHz as defined by FCC. The antenna exhibits nearly omnidirectional radiation pattern and a gain ranging from 1 dBi to 6.8 dBi within the operating frequency range (1.8 GHz-11 GHz). An equivalent circuit model of the proposed antenna is developed, and the circuit response is obtained. All the measured results are found in good agreements with the simulated ones. The proposed antenna is suitable for applications in Wi-Fi, IEEE 802.11a Wireless LAN, WiMAX, ISM bands, wireless communications, etc.