Mutual Coupling Reduction in MIMO Microstrip Patch Array Using TM₁₀ and TM₀₂ Modes

Abstract

A novel decoupling method is investigated for the multi-input multi-output (MIMO) microstrip patch antenna (MPA) array. This method makes use of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> modes, which are simultaneously excited in the rectangular MPA. It is found that by adjusting the frequencies of the two modes, their <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -fields coupled to the adjacent passive MPA can counteract each other to generate a specific null-field region. When the feeding position of the passive MPA is located in the null-field region, the MPA cannot be excited effectively, and hence an extremely low mutual coupling is obtained without requiring any extra decoupling structure. To validate the feasibility of this decoupling method, an E- and an H-plane-coupled <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> MIMO MPA arrays are respectively simulated, fabricated, and measured. The isolation of the E-plane-coupled array is enhanced from ~11 to 57 dB, while that of the H-plane-coupled array is improved from ~18 to 51 dB.