Wideband Decoupling for Tightly Placed Stacked Patch Antenna Based on Lumped and Distributed Elements

In this letter, an effective decoupling strategy with multiple lumped and distributed hybrid elements is proposed to enhance isolation between tightly placed stacked patch antennas. To start with, a novel capacitor-loaded defect ground structure and a lumped inductor are combined to adjust antenna system's differential mode (DM) impedance. Then, a metal strip grounded with two lumped capacitors, is employed to tune common mode (CM) impedance to coincide with that of DM, thus implementing excellent reduction of mutual coupling. Here, more importantly, through equivalent magnetic-current analysis, it is found that the CM and DM impedance of mirrored and translated stacked patch antennas alternatingly correspond to each other. Thereby, the proposed method demonstrates effectiveness for stacked patch antenna pairs with mirrored and translated arrangements. To validate the concept, a prototype is fabricated and measured. The experimental results manifest that original poor isolation of −5 dB is significantly enhanced to better than −20 dB over −10-dB impedance bandwidth of 3.30 GHz to 3.80 GHz (14.1%), with a close center-to-center spacing of 0.24<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>.