In this paper, a novel configuration of circular ultra-wideband (UWB) antenna with band rejection characteristic is presented. In order to obtain this characteristic, the spiral loop resonators resonating at the rejection frequency are located in both sides of the circular radiating patch. This novel structure provides the band-notched characteristic without the degradation of the UWB antenna performance itself. Furthermore, the notched band can be easily tuned by adjustment of resonator dimension because the size of the spiral loop resonators controls the corresponding resonance frequency. This prototype antenna has been fabricated on a substrate, Rogers 4003, with the thickness of 0.8 mm and relative permittivity of 3.38. The fabricated UWB antenna covers the frequency band from 3.1 to 11.23 GHz (S_11 <-10 dB), and the band rejection characteristic appears near at 5.8 GHz band to which the wireless LAN service is assigned. And the far-field radiation patterns of the proposed antenna show omnidirectional and stable over the whole frequency band, which prospects the deployment in the UWB system. The measured results agree well with the simulation by the Microwave Studio of CST. This novel technique utilizing the spiral loop resonators might be useful to the planar antennas requiring the band rejection characteristics.
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