A Compact Broadband Self-Decoupled MIMO Array Based on Dual Transmission Path Cancellation

A compact broadband multiple-input–multiple-output (MIMO) array consisting of four identical self-decoupled antenna pairs (SDAPs) is proposed in this letter. The SDAP, which has two feeding ports and a shared radiator, is first introduced. A dual transmission path cancellation method is proposed to achieve the broadband self-decoupling capability. The most of the energy transferred on the two transmission paths from one port can be well cancelled in the other port. As a result, high isolation can be obtained between the two ports. In addition, the coplanar waveguide transmission line and a pair of H-shaped sheets widen the operating band of the SDAP. The size of the proposed SDAP is 0.25<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> × 0.08<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> is the free-space wavelength at 3.8 GHz). An 8 × 8 MIMO array is fabricated and measured to assess the performance. The measured overlapping impedance bandwidth under −6 dB is 3.2 GHz to 4.4 GHz (31.6%). The isolations of all ports are better than 12 dB with a peak value of 35 dB. The measured total efficiency varies from 46% to 77%, and the envelope correlation coefficient is less than 0.11.