A Miniaturized Wideband Circularly Polarized Antenna Based on Tightly Coupled Monopole

This letter presents a miniaturized wideband circularly polarized (CP) antenna based on a tightly coupled monopole operating in the UHF band. Initially, a tightly coupled wideband monopole is employed as the radiation unit, showcasing its potential for broadband operation. A two-layer compact wideband sequential feed network (WSP) is then designed to connect these elements, featuring a higher efficiency compared to the one employing the low-temperature co-fired ceramic technology (LTCC) technology. As a result, the antenna was reduced to 0.08 λ0in height and 0.15 λ0in diameter, offering practical advantages in terms of installation and form factor. Finally, the rotation direction of radiation elements is analyzed to achieve a stable beam width. The proposed antenna is fabricated and tested. The results demonstrate that the antenna attains a wide impedance bandwidth and axial-ratio (AR) bandwidth of approximately 80% (VSWR < 2.0) and 67% (AR < 3 dB), respectively. Additionally, a stable radiation pattern is obtained throughout the entire operating band.