A compact planar self-affine sierpinski carpet fractal monopole antenna with band notch characteristics for ultra wideband communications

Abstract

This paper presents a novel compact planar self-affine sierpinski carpet fractal monopole coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with improved gain, radiation efficiency and a sharp band-notched characteristics for the rejection of interfering WLAN (5.15---5.825 GHz) assigned for IEEE 802.11a narrow band communication system. The significant improvements in gain and radiation efficiency are achieved by the introduction of carpet fractals in the radiating circular patch. The antenna covers the entire UWB frequency band (3.1---10.6 GHz) with voltage standing wave ratio (VSWR) ≤ 2 which depicts optimum impedance matching of the proposed antenna structure. The antenna occupies a compact size of 36 × 41 mm2 and band rejection is achieved by embedding compact C--shaped slots with folded arms on the ground planes of the CPW feed lines which yield a very sharp notch for WLAN band. The band rejection is demonstrated by a high value of VSWR around notch frequency. Compact self-affine sierpinski carpet fractals are introduced in the radiating circular patch to improve performance of the UWB antenna. The proposed fractal antenna exhibits improved gain that varies from 2 to 6 dBi and optimum radiation efficiency which varies from 85 to 99.9 % over the UWB frequency range. The gain and radiation efficiency are suppressed with strong dips at the desired rejection WLAN band. Omnidirectional radiation characteristic is achieved over UWB frequency range which supports the uniform transmission of signal irrespective of the orientation of the antenna direction.