An antenna array formed by four PIFA elements located very close to each other, with low inter-element matching for MIMO applications is proposed. The antenna array consists of four F-inverted wideband radiators, with a fractional bandwidth around 56%, spaced one to each other by a very short distance (< 0.065 λ0) at a centre frequency of 2.55 GHz. The operational bandwidth goes from 1.88 to 3.15 GHz considering the Sii < -10 dB at each port. Moreover, the coupling among ports reaches values below Sij < -10 dB and getting values less than -30 dB at 1.8 GHz, just by employing an uncomplicated technique implemented by a neutralization line between elements. The antenna array gain goes from 2 dB to 6 dB over the operating bandwidth. Concerning MIMO figures of merit, the radiation pattern of each element is orthogonal to each other. The Envelope Correlation Coefficient is below 0.04 at the designed frequency, reaching a peak around 0.082 at 1.8 GHz, but still achieving the requirement for MIMO operation (less than 0.5). The Total Active Reflection Coefficient (TARC) is almost convergent at the design frequency, showing low dependence on random signals at different elements, and finally, the diversity gain reaches values close to 20 dB, making the array suitable for MIMO access point applications.
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