A new planar multiple-input–multiple-output (MIMO) antenna for ultra wideband (UWB) applications is presented. The proposed antenna operates over the frequency band from 3.1 to 10.6 GHz and it consists of two identical circular monopoles on an FR4 substrate. The wide isolation is achieved through a novel planar decoupling structure that is being inserted between the dual antennas. Moreover, a center slot is etched on the common ground to further increase isolation. The effectiveness of the decoupling structure is analyzed, and performance study has been performed to investigate the mutual coupling reduction. A good isolation of more than 31 dB has been achieved through the entire UWB band (more than 12 dB improvement over the reference antenna). The proposed UWB antenna with and without the wideband decoupling structure has been investigated and verified both numerically and experimentally. The measurement results of the proposed UWB–MIMO antenna are in good agreement with the simulation results. The proposed UWB antenna has been compared with previous works regarding antenna size, geometric complexity, bandwidth, and isolation level. The proposed antenna has some outstanding characteristics such as a geometric simplicity, compact size, broad bandwidth, and low correlation which give the antenna an excellent diversity performance and a good candidate for UWB applications.

This work shows the effect of a novel Fractal based Electromagnetic Band Gap (FEBG) structure between dual PIFAs antenna elements. The FEBG structure without any shorting pins builds on a well-known fractal structure called Sierpinski carpet, where two iterations have been applied as a uniplanar EBG between dual PIFAs elements to increase the isolation. The proposed antenna can operate at approximately 2.65 GHz for wireless Long Term Evolution (LTE) application with compact design dimensions. The simulations are carried out with Ansoft HFSS ver 17.0. The second iterative order FEBG band-gap characteristic is verified using more computationally efficient analysis. An investigation on coupling reduction showed more than 27 dB, and 40 dB in E-plane and H-plane; respectively between the dual antenna elements is achieved for an antenna spacing less than half wavelength. The proposed antennas with and without second iterative order FEBG are fabricated and measured. The measurement results are in good agreement with the simulated results. Moreover, the envelope correlation of antenna elements with the proposed FEBG is quite smaller than that of antenna elements without FEBG, which gives the proposed system an excellent diverse performance and suitable for the use in low-frequency narrow-band MIMO applications.

GHz are obtained, respectively, in the simulation and measured responses. | C ONCL US I ONSThe third and fifth order microstrip LPFs are designed with folded line in place of high-impedance line. In addition to the reduction in overall size of filter by near about 10%, our simulated results have shown no effect on the cutoff frequency of filters with folded high-impedance line in comparison to the conventional LPF. Among the salient features, the lower insertion loss in pass band, higher sharp cutoff rate and higher attenuation in the stop band are obtained with the proposed LPF design. Results of fifth order simulated and measured LPF are found in good agreement. In future, these features can be further improved by utilizing 'C', 'X', or 'S' shaped folded line in addition to size reduction. ACKNOWLEDGMENTSThe authors thank the Research and Development Scheme 2015-2016 of the University of Delhi for the financial support and carrying out the present work. ORCID Kamlesh PatelAbstract An all-resonator based triplexer is presented using a double-stub-loaded resonator (DSLR) that acts as a F IGUR E 6 Comparison of simulated and measured responses: A, S 11 (dB), B, S 21 (dB) [Color figure can be viewed at wileyonlinelibrary. com] EL-TOKHY ET AL. | 1815 F IGUR E 6 Triplexer measurement versus simulation. (A) Transmission, (B) reflection, and (C) isolation between the three output ports [Color figure can be viewed at wileyonlinelibrary.com]

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