Decoupling of Tightly Placed Square Patch Antenna Pairs With Different Performances by a Simple and Compact Structure

In this letter, a simple and compact decoupling structure is presented, which is embedded at the center of the antenna pair without the demand of extra space. It is composed of only one small metal pad and one via hole, and its working mechanism is clearly explained with resorting to the equivalent circuit model. The metal pad works with the patches to function as the parallel plate capacitors, while the via hole can be modeled as an inductor. The circuit analysis reveals that the transmission zero can be produced with the proposed decoupling structure. On this basis, one square patch antenna pair with 0° polarization, as well as two 45° polarized antenna pairs operating with single and dual resonant modes, respectively, are constructed. These three design examples demonstrate that the proposed decoupling structure is equipped with its powerful ability in strong-coupling suppression and is available for antenna pairs with different polarizations and resonant performances. The measured results of the 45° polarized dual-mode antenna pair indicate that an impedance bandwidth of 6% is realized with the low profile of 0.0325 free-space wavelength (<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>), while the isolation is remarkably enhanced from 4.5 dB to 20.0 dB within the passband with the edge-to-edge spacing of 1.5 mm (0.015<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>) and center-to-center spacing of 32.5 mm (0.325<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>).