A Floquet Series-Based Framework to Evaluate the Impact of Antenna Efficiency on MIMO Systems

Antenna efficiency is a key parameter in the design of large-scale dense arrays, and influences the signal-to-noise ratio (SNR) of wireless communications. Low embedded element efficiency (EEE) has been verified to be the bottleneck of dense array MIMO systems. Using ideas from the Floquet series, we propose a new framework to evaluate the mutual coupling for infinite arrays with a regular grid, including two new methods to calculate the EEE. The proposed methods can incorporate the impedance of the source network, whereas the traditional geometry based method assumes perfect impedance matching at all scan angles. Starting from the surface current of array elements, the radiation field is decomposed into a set of current-weighted orthogonal electromagnetic waves. This decomposition can be utilized to compute the radiation characteristics of the antenna array, including the active impedance, the generalized scattering parameters, and the embedded element patterns. Theoretical analysis is provided to illustrate how the degradation of EEE reduces the SNR and sequentially channel capacity of MIMO systems. Numerical simulations show that the proposed methods give a more accurate efficiency than the geometry based method. Channel capacity based on the polarization holographic channel model is evaluated to validate the constraining effect of EEE on system throughput.