A dipole sub-array with reduced mutual coupling for large antenna array applications

The use of large array antennas in multiple-input multiple-output (MIMO) exploits diversity and reduces the overall transmission power making it a key enabling technology for 5G. Despite all the benefits, mutual coupling (MC) between elements in these array antennas is a concerning issue as it affects the antenna terminal impedance, reflection coefficients, etc. In this paper, a four-element printed dipole sub-array with reduced MC for S-band has been proposed. A balanced transmission line structure has been designed with two dipole arms on the opposite side of the substrate. Simulated and measured results are in good agreement making the design suitable for large array applications such as phased array radars. The proposed array exhibits good impedance matching with a reflection coefficient of -45 dB and resonating at the center frequency of 2.8 GHz. Moreover, isolation of -20 dB has been achieved for each element in a 2×2 planar array structure using out of band, parasitic elements, and planar shift by distributing the separation between the elements

Effects of mutual coupling on lattice reduction-aided millimeter wave hybrid beamforming

Millimeter wave (mmWave) communications has gained considerable attention due to the availability of large bandwidths, which can be harnessed to meet the ever-increasing data rate demands. Directional beamforming combined with baseband precoding should be used owing to the high propagation losses encountered at mmWave frequencies. This is typically referred to as hybrid beamforming. In hybrid beamforming arrangements, the adjacent antenna elements are closely spaced, typically at half-wavelength spacing in order to compensate for the propagation losses. In this antenna array configuration, the mutual coupling between the adjacent antenna elements becomes significant and may limit the performance of the system. Therefore, in this paper, we propose a reduced-complexity near-optimal detection scheme, namely the so-called Element-based Lattice Reduction algorithm, for hybrid beamforming in mmWave communications and we investigate its performance in the presence of mutual coupling. We demonstrate that the mutual coupling affects the spatial correlation of the channels between the different antennas depending on the distance between the antenna elements, which has a direct effect on the achievable rate as well as bit error ratio (BER) performance of the system