Abstract
In this paper, a method to reduce the inevitable mutual coupling between antennas in an extremely closely spaced two-element MIMO antenna array is proposed. A suspended meta-surface composed periodic square split ring resonators (SRRs) is placed above the antenna array for decoupling. The meta-surface is equivalent to a negative permeability medium, along which wave propagation is rejected. By properly designing the rejection frequency band of the SRR unit, the mutual coupling between the antenna elements in the MIMO antenna system can be significantly reduced. Two prototypes of microstrip antenna arrays at 5.8 GHz band with and without the metasurface have been fabricated and measured. The matching bandwidths of antennas with reflection coefficient smaller than −15 dB for the arrays without and with the metasurface are 360 MHz and 900 MHz respectively. Using the meta-surface, the isolation between elements is increased from around 8 dB to more than 27 dB within the band of interest. Meanwhile, the total efficiency and peak gain of each element, the envelope correlation coefficient (ECC) between the two elements are also improved by considerable amounts. All the results demonstrate that the proposed method is very efficient for enhancing the performance of MIMO antenna arrays.
Highlights
(1) Side-lobes might occur and it will affect the beam-scanning capability of the array3,4. (2) The SNR of the array will be deteriorated as unwanted coupling between elements will cause data streams received by other antenna elements rather than radiating into free space2. (3) The envelop correlations between elements become high data throughput is significantly reduced5,6. (4) Gain and total efficiency of the array will drop since effective radiated power are coupled elsewhere and dissipated on the loads of the antenna elements[2]
Only a few of them can be readily extended to Massive MIMO antenna arrays with dozens of elements
If we look at the band from 5.6 GHz to 6 GHz, the isolation performance of the array with 7 × 5 split ring resonators (SRRs) units is better than the array with 8 × 6 SRR units
Summary
(1) Side-lobes might occur and it will affect the beam-scanning capability of the array3,4. (2) The SNR of the array will be deteriorated as unwanted coupling between elements will cause data streams received by other antenna elements rather than radiating into free space2. (3) The envelop correlations between elements become high data throughput is significantly reduced5,6. (4) Gain and total efficiency of the array will drop since effective radiated power are coupled elsewhere and dissipated on the loads of the antenna elements[2]. (2) The SNR of the array will be deteriorated as unwanted coupling between elements will cause data streams received by other antenna elements rather than radiating into free space. (4) Gain and total efficiency of the array will drop since effective radiated power are coupled elsewhere and dissipated on the loads of the antenna elements[2]. Metamaterial based or inspired solutions[20,21,22,23,24,25] are becoming popular, but most of them are very effective for arrays with limited number of antennas where inter-element spacing is moderate (no less than 0.1 λ0). The idea of covering a metasurface over an antenna for performance enhancement is not new, but most of them are not used for array antenna decoupling, they are used
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