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A compact circular fractal antenna element loaded with a central pentagonal slot is presented in this paper. This structure consists of a fourth iterative radiator fed by a partially tapered feed line and CPW defected ground plane. A superwide impedance bandwidth of 3.45-52.17 GHz ($175% fractional bandwidth) is achieved. Two multiple input multiple output (MIMO) configurations are also designed and analyzed by using this antenna element. For spatial and pattern diversity configurations, the impedance bandwidth of 3.45-52.2 and 3.1-52.2 GHz are achieved, respectively. The optimized footprints of antenna element, spatial diversity configuration, and pattern diversity configurations are 28 Â 24, 28 Â 53, and 45 Â 48 mm 2 , respectively. The isolation for both MIMO configurations is more than 20 dB in maximum portion of the operating bandwidth. Desirable radiation and diversity performance characteristics are achieved for antenna element and MIMO configurations. The wide bandwidth, compact dimensions along with good radiation, and diversity performance characteristics make the proposed antenna configurations suitable for integration in superwideband wireless communication systems. A good agreement between the experimental and simulation results is observed.coplanar waveguide feeding, defective ground structure, fractal antenna, MIMO applications, superwideband applications, tapered feed line | INTRODUCTIONAfter the allocation of unlicensed frequency spectrum 3.1-10.6 GHz for ultrawideband (UWB) applications by Federal Communication Commission (FCC) in 2002, both academic and industry researchers started making efforts for the integration of UWB technology in wireless communication systems. This integration resulted in secure wireless communication services at high data rates over a wide range of frequencies. With the advancement in technology, the demands for security, data rate and wide bandwidth increased exponentially. These demands required antenna structures which can provide service for both short-range and long-range communication (already covered by UWB spectrum). To fulfill these demands, a new technology, that is, superwideband (SWB) technology, having ratio bandwidth of 10:1 or more is defined. To integrate SWB technology in wireless communication systems, several antenna structures were explored to operate over a wide range of frequencies and can be integrated with compact communication devices. Among the various explored antenna structures, monopole antennas are found be good candidates who can provide

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