Wideband, High-Density Circularly Polarized Array with Reduced Mutual Coupling and Enhanced Realized Gain

A planar single-layer parasitic swastika-shaped structure, which serves as an effective isolator, is developed for mutual coupling reduction in wideband, high-density circularly polarized (CP) arrays. A closely spaced two-element CP antenna array demonstrates the efficacy of the approach. The currents induced by the CP coupling are effectively cancelled out when this isolator is integrated into it. The antenna elements are co-planar. They are arranged with a center-to-center distance of 0.4 λL (λL being the wavelength of the lower bound of the array’s operational bandwidth) and have an extremely small edge-to-edge distance of ~ 0.024 λL. The parasitic element yields an increase of the isolation level between the antenna elements of more than 9.4 dB over the entire operational band, with a maximum improvement of 20.4 dB. Moreover, the antenna elements realize a modest maximum gain improvement of ~ 1.2 dB in the boresight direction over the same band. The overlapped impedance matching and 3-dB axial ratio (AR) bandwidths cover the range 1.7-2.7 GHz, a ~ 45% fractional bandwidth. A prototype was fabricated and measured; the measured results are in good agreement with their simulated values.