Triband Circularly Polarized Unidirectional Stacked Patch Array Antenna Enabled by Broadband Feed Network

In this work, the design of a triband circularly polarized antenna which consists of a stacked patch antenna array and a wideband quadrature four-port feed network is reported. Using a grounded shunt λ
g
/4 stub in the main line of a conventional phase shifter, four signals with equal amplitude and orthogonal phase of 0°, 90°, 180°, and 270° can be achieved in a frequency bandwidth greater than 67% from 5 to 10 GHz. Benefiting from stacked microstrip patches and the sequentially rotated feed layout, the proposed antenna exhibits a low profile and symmetrical unidirectional radiation beam. The overall electrical size of the antenna is $1.6 \times 1.4 \times 0.06\;{\lambda _0}^3$ (λ
0
is the free space wavelength at 6.0 GHz). In addition, the antenna features the same circular polarization status at three bands, the 3 dB axial ratio bandwidths are 15.2% (5.4-6.2 GHz), 11.4% (6.7-7.4 GHz), 15.3% (7.7-9.0 GHz), and the forward peak gains are 8.3, 9.8, 6.3 dBic at 6, 7, and 8.5 GHz, respectively.