In this letter, a compact octagonal shaped fractal ultrawideband multiple-input-multiple-output (MIMO) antenna is presented and its characteristics are investigated. In order to achieve the desired miniaturization and wideband phenomena, self-similar and space filling properties of Koch fractal geometry are used in the antenna design. These fractal monopoles are placed orthogonal to each other for good isolation. Moreover, grounded stubs are used in the geometry to provide further improvement in the isolation. The band rejection phenomenon in wireless local area network (WLAN) band is achieved by etching a C-shaped slot from the monopole of the antenna. The proposed antenna has compact dimensions of 45 mm × 45 mm and exhibits quasi-omnidirectional radiation pattern. In addition, it shows an impedance bandwidth (S 11 <-10dB) from 2-10.6 GHz with isolation better than 17dB over the entire UWB range. Diversity performance is also evaluated in terms of ECC and capacity loss. The measured results show good agreement with the simulated ones.

In this study, a design approach to achieve multiresonance phenomena in ultra‐wideband (UWB) bandwidth using fractal geometry is investigated. The introduction of Koch fractal geometry in monopole as well as in the ground plane of the antenna generates additional resonances, which helps to achieve entire UWB operational bandwidth. Therefore the bandwidth is increased up to 122%. Moreover, the fractal nature of the antenna also facilitates to obtain the stable radiation pattern. The compact dimension 31 mm × 28 mm of the antenna exhibits nearly omnidirectional radiation pattern, with good reflection coefficient over the entire UWB frequency range. The proposed prototype is fabricated and its measured results are in good agreement with the simulated one. The time‐domain analysis of the antenna is performed and it is found that fidelity factor is better than 0.81, which shows good pulse preserving capability of the antenna.

In this letter, a Minkowski‐like fractal geometry‐based ultra‐wideband (UWB) monopole antenna is proposed and investigated. The radiator of the antenna is designed using similar segments of the Minkowski‐like structure. The multiple resonance phenomena of fractal geometry are utilized in the proposed structure to obtain the wideband operability by repetition of similar segments in the radiator structure of the antenna. The self‐similar nature of this geometry provides higher effective antenna length and wide operating bandwidth. The multiple slots are introduced in the ground plane to improve the reflection coefficient over the entire UWB frequency range. The proposed antenna has an optimized dimension of 23.5 × 26.5 mm2 and shows the operating bandwidth from 1.4 to 10.4 GHz. The proposed design is fabricated, and its measured result shows good agreement with the simulated one. The proposed antenna exhibits nearly omnidirectional radiation pattern, proper impedance matching over the entire UWB frequency range. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2273–2279, 2014

Abstract-In this paper, a compact multiple-input-multiple-output (MIMO)/diversity antenna with WLAN band notch characteristics, high isolation, and good ECC suitable for portable ultra-wideband (UWB) applications is presented. The proposed antenna has optimized dimensions of 29 mm × 38 mm. The antenna consists of two orthogonal circular monopoles with a 50 Ω microstrip feed line. In addition, to enhance the impedance bandwidth, a fractal slot, created using Minkowski fractal geometry, is introduced into the ground plane, which is located on the other side of the substrate, just below the feed line. Good isolation (≥ 21.5 dB) with a fractional bandwidth up to 220% is achieved between antenna elements by introducing two ground stubs and a rectangular slot in the ground plane. A band-notch characteristic in the WLAN band is obtained by etching an elliptical split-ring resonator (ESRR) in the radiator. Moreover, a diversity performance of the antenna in terms of ECC (< 0.01) and capacity loss (< 0.3 b/s/Hz) is performed. This paper offers, for the first time, a combined effect of fractal geometry and ESRR geometry in an antenna design. Finally, a comparison of the proposed antenna is performed with the UWB MIMO/diversity antennas existing in the literature. These results show the suitability of the presented antenna for portable UWB systems.

In this letter, a compact ultrawideband (UWB) multi‐input‐multi‐output (MIMO) antenna with cross‐shaped unconnected Ground stub using characteristic mode analysis (CMA) is presented. The proposed work consists of two elliptical shape monopole UWB antenna with a cross‐shaped stub in the ground plane. The compact MIMO antenna has the dimension of 25 × 25 × 1.6 mm3. These monopoles are able to excite several characteristic modes (CMs), which support to wideband resonance, and cross‐shaped stub support CM at lower frequency band in the ground plane and reduces mutual coupling between monopoles. The UWB MIMO antenna is resonating in frequency bands from 2.97 to 13.8 GHz bandwidth with a good mutual coupling (<−15 dB). The diversity performance envelop correlation coefficient (ECC) and diversity gain (DG) of the antenna are less than 0.05 and more than 9.97, respectively. The experimental result confirming a good treaty with the simulated ones, so that the proposed antenna is suitable for compact UWB MIMO applications.