Bandwidth and Isolation Improvement of Highly Coupled Printed Array Antenna Using Multiple Shorting Posts
Reza Zaker, Ali Kheirdoost
Abstract
A novel broadband matching and decoupling network (MDN) for symmetric two-element array of microstrip patch antennas is proposed. As a distributed multiple inductive-capacitive loading, this MDN employs two groups of parallel shorting posts (vias) on the nonradiating edges of the high-coupled patches with a very-low edge-to-edge distance. This MDN excites two controllable new modified resonant half-modes, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,1</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3/2,0</sub> , whose aggregation provides a well-matched broad bandwidth with broadside pattern. Furthermore, a reasonable offset between these two groups of vias helps obtaining a balance between the mutual capacitive and inductive couplings, and then a broadband high isolation across the overlapped bandwidth without using the conventional large isolating structures. A resonator-based equivalent-circuit model including different mutual and cross couplings is proposed and discussed to study the coupling mechanism between the modes and the antennas. Finally, the measurement proves a bandwidth of 9.8% (3.38–3.73 GHz) with an enhanced isolation of over 27 dB. A fair comparison with the state-of-the-art approaches is drawn, and greatly reduced spatial correlation (with envelop correlation coefficient (ECC) of less than 0.06) and over 72% total efficiency (with 25% increase) make the proposed design appropriate for fifth-generation (5G) multi-input–multi-output (MIMO), and the other sensitive bi-element systems.