A Conical Cavity-Backed Antenna With Embedded Multiple Quarter-Wave Resonators

A conical cavity-backed antenna with embedded multiple quarter-wave resonators (multiple QWRs) is proposed. The 3-dB axial ratio bandwidth (ARBW) of a cavity-backed antenna is limited by cavity resonance, undesired cavity current, and circular polarization (CP) behavior of the radiator. As a result, the cavity-backed antenna exhibits a high AR level and narrows the 3-dB ARBW, even though a high antenna gain and front-to-back ratio remain. In this study, a simple crossed-dipole was used to excite a conical cavity with four embedded multiple QWRs. The multiple QWR consists of two metallic plates and a cavity rim wall, which generate an additional current to support CP radiation. A conical cavity with embedded multiple QWRs can reduce the AR level and enlarge the 3-dB ARBW by preventing cavity resonance which creates a strong electric field inside the cavity, minimizing the effect of the undesired cavity current that radiates the cross-polarized wave, and further adding the CP mode to the antenna. The prototype realized a wide impedance bandwidth of 93.83% (1.72-4.76 GHz) and wide axial ratio bandwidth of 83.75% (1.86-4.54 GHz). The maximum gain was 9.9 dBic at 4.18 GHz. For the case where the radiator cannot be changed, this study demonstrates a cavity approach utilizing a microwave structure (multiple QWR) to reduce the AR level and maximize the 3-dB ARBW of a cavity-backed antenna without radiator modification.