We present a wideband circularly polarized (CP) multiple-input multiple-output (MIMO) dielectric resonator antenna (DRA) with enhanced diversity. In the DRA element, two diagonal edges of the DR were truncated at 45 • to obtain a wider axial ratio larger than 0.65 GHz. The DRA element was excited by a cross-ring slot with specific slot-arm ratio through microstrip-line (MSTL) implemented at the backside of the FR4 substrate to generate CP fields. Small triangular stands at the edge of the DR were employed to hold it in place to avoid any degradation from the uncontrollable bonding agent used for attaching DR onto the FR4 substrate. The DRA achieved an impedance bandwidth better than 0.8 GHz with an antenna gain of 4.83 dBi. Using the DRA with the MSTL feed, two-element CP-DRA array was implemented with electromagnetic band-gap (EBG) structure etched onto the ground plane of the MSTL. The proposed architecture achieves isolation better than 26 dB over the desired frequency band without any performance degradation while maintaining its compact size in the array. Various diversity analysis was carried out on the implemented circularly polarized MIMO DRA. The measured results demonstrated that the proposed singly fed DRA with EBG on the ground plate is suitable for implementing wideband circular polarized MIMO antennas in a compact size.INDEX TERMS Dielectric resonator antennas, electromagnetic band-gap, MIMO, mutual coupling.
In this paper, we propose the use of resistor-loaded paired parallel-coupled resonators (PCRs) for mutual coupling reduction and isolation enhancement in wideband MIMO array antennas. It was shown that the isolation enhancement using a conventional PCR structure was drastically degraded in the middle of the frequency band. By placing an optimally designed resistor between the PCRs, we can improve the isolation considerably, compared with the simple PCR structure. Moreover, it could also improve the diversity parameters, such as envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CCL). The validity of the proposed resistor-loaded PCR technique was verified with ultrawideband array antennas with 1 × 2 and 1 × 4 patch array configurations, achieving a 0.125λ 0 center-tocenter spacing between narrowly spaced patches and isolation better than 25 dB within the range 3-9-GHz without any degradation in its frequency response, radiation patterns, or diversity parameters. The presented results confirm that the proposed technique is suitable in various MIMO systems applicable for wireless local area networks (WLANs), long-term evolution (LTE), and possibly fifth-generation (5G) communication due to the compact size and improved isolation performance. INDEX TERMS Antenna arrays, multiple-input multiple-output (MIMO), mutual coupling.
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