Decoupling for Closely-Spaced Co-Polarized Antennas Using Heterogeneous Elements

Heterogenous array is studied in this paper to obtain the low in-band mutual coupling between two closelyspaced co-polarized antennas. By the characteristic mode analysis of a slotted rectangular patch, the linearly polarized mode with bidirectional radiation is selected to form an array with a dipole. Feeding structure is proposed to purely excite the patch mode. Due to the orthogonality of the patch mode and dipole mode, the two-element heterogenous array achieves high isolation of 28.6 dB with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\lambda}/\boldsymbol{4}$</tex> array spacing, which is much higher than the array with two identical dipoles.