High Isolation Compact Four-Port MIMO Antenna Loaded with CSRR for Multiband Applications

In this paper, a compact 4 x 4 multiple-input-multiple-output (MIMO) patch antenna has been presented for triple band operation. Out of the 4 antennas, two are tuned to cover DCS (Digital Cellular System) downlink and two are tuned to cover DCS uplink frequency separately along with two common operating frequency centered around 2.45 GHz and 875 MHz. Four complementary split-ring resonators (CSRRs) have been etched in the ground plane exactly below the four patch antennas for attaining compactness from 0.36 lambda(2)(0) to 0.13 lambda(2)(0). In addition to this, by optimizing CSRRs outer radius, one lower common band operation of around 875 MHz (0.031 lambda(2)(0)) has been obtained. Two, square split-ring resonators (SRRs) are placed between patch antennas to increase isolation by almost 7 dB around DCS band. The proposed MIMO antenna has been fabricated on an FR4 substrate (60 x 60 x 0.8) mm(3) with dielectric constant, epsilon(r) = 4.3 having an antenna area of 0.13 lambda(2)(0). The Proposed MIMO antenna has two common operating bands, 850-900 MHz, 2410-2466 MHz and one individual band from 1725-1770 MHz for one group of two antennas of dimensions 17 x 22 mm(2) and another individual band from 1800-1845 MHz for another group of two antennas of dimensions 17 x 23 mm(2), where reflection coefficient is less than -10 dB with a minimum isolation of 17 dB. Diversity performance of the proposed MIMO antenna has been verified experimentally on all three bands. However, there is a slight deviation in the DCS operating band due to two different groups of antennas.