A 4×4 slot MIMO antenna for WLAN application

The correct application of total active reflection coefficient to evaluate MIMO antenna systems and its generalization to N ports

“…It is remarkable that and TARC for multiport antennas and MIMO arrays, respectively, are mainly differentiated by the consideration of the input feeding phases; Equation permits to calculate a family of curves by substituting random values of θ in the range between 0 and 2 π . However, the assumption of lossless antennas is valid for both definitions .…”

“…To satisfy this equation, θ = | φ 11 − φ 12 | = | φ 21 − φ 22 |, a condition that can be accomplished a reduced number of times throughout frequencies, and if and only if the scattering matrix is perfectly symmetrical. In this case, if the “coupling coefficients” values, namely S 12 and S 21 magnitudes, are lowered by one or more isolation techniques, and S 12 = S 21 , TARC reflects the behavior of the reflection coefficient of a single antenna . Indeed: …”

“…Works demonstrate the case when the TARC equation is used correctly for N antennas. In Reference , S 31 and S 41 magnitudes are noticeably lesser than S 21 , S 32 , and S 11 , as reported on their figure number 3.…”

“…Although the dispersion of curves can be seen in magnitude and frequency, their general trend is dictated by the S 11 parameter. The magnitudes of all S ‐parameters in Reference are comparable and their reported TARC family shows similar behavior.…”

“…However, several authors have issued on leading journals on Antennas and Microwave Techniques imprecise equations to compute TARC on MIMO antennas, which disregard the information of random phases, and its impact on the performance of the antenna system vs frequency. After an examination of the state‐of‐the‐art on MIMO arrays performed by the authors of this work, it was found that many papers reported a correct evaluation of TARC expression by displaying a family of curves, given by the variations on the random phases θ i , along with the computation of other adequate antenna metrics. Whereas in several other papers a wrong version of the equation was used; or only one curve was displayed without a mathematical explanation of how it was derived; only one value at the resonance frequencies was reported in a table; and, finally, one curve obtained by averaging an unknown number of TARC curves was given .…”