Isolation enhancement of compact co-polarized circular patch antennas using embedded series resonator

An embedded series resonator for compact co-polarized circular patch antenna pairs is presented in this paper. With a compact center spacing (CS) of 0.32 lambda 0 and edge spacing (ES) of 0.03 lambda 0 (lambda 0 is the free-space wavelength at the center frequency), strong mutual coupling inevitably arises. However, by introducing a cross-shaped fence and two quarter-wavelength open-ended slots onto a circular patch, port isolation of the first proposed antenna pair is significantly enhanced by 25.2 dB within a bandwidth of 6.2%. Moreover, the effectiveness of the embedded series resonator is demonstrated by achieving a wider 20-dB decoupling bandwidth of 10.4% for the second proposed compact bandwidth-enhanced antenna pair. For validation, both proposed prototypes are fabricated and measured, showing good agreement between measurements and simulations. To demonstrate the universality, a 1 x 8 patch array with an embedded series resonator can achieve a beam scanning angle of +/- 70 degrees with a gain attenuation of 2.6 dB. Benefiting from compact size, high isolation, and enhanced decoupling bandwidth, the proposed designs hold promising potential for application in multiple-input multiple-output system and antenna array.