Dual-band circular polarised square-ring patch antenna loaded lumped capacitors

Herein, a dual-band circularly polarised (CP) antenna for adjustable frequency ratio is proposed. The proposed antenna consists of two square-ring patches with a gap on the stacked substrates. A capacitor is inserted within the gap of each square-ring patch. The two square-ring patches have two resonant frequencies, because the additional resonant frequency is generated by the gap. The two first resonant frequencies of each square-ring patch combine to form the low band and two second resonant frequencies combine to make the high band. In the low band, as the gaps of the two square-ring patches are located on different diagonals, the two first resonant frequencies are orthogonal to each other. In the high band, as the second resonant frequency is perpendicular to the first resonant frequency, the two second resonant frequencies are also orthogonal to each other. In the measurement results, the low and high bands achieve −10 dB bandwidths (BWs) of 3.75 and 2.49%, 3 dB axial ratio BWs of 0.99 and 0.53%, and gains of 1.89 dBi and 0.64 dBi, respectively. By appropriately changing the values of two capacitors, frequency ratio has an available range from 1.065 to 1.336.