Compact Circularly Polarized Dualband Zonal-Slot/DRA Hybrid Antenna Without External Ground Plane

A zonal slot antenna cut onto a conducting cavity is combined with a dielectric resonator antenna (DRA) to form a circularly polarized (CP) dualband hybrid antenna. The zonal slot antenna and DRA are located on the side wall and top face of the cavity, which are responsible for the lower and upper bands, respectively. No external ground planes are used for the hybrid antenna and, thus, the structure is very compact. An L-probe is placed inside the cavity to feed the zonal slot directly and to excite the DRA indirectly through a cross coupling slot beneath the DRA. In this paper, two symmetrical cuts are cut onto the zonal slot for exciting CP fields, and a third cut is introduced to the zonal slot to fine-tune the axial ratio (AR). The DRA is excited by its underlaid cross slot with unequal lengths, giving two orthogonal degenerate modes that generate CP fields. The frequencies and field polarizations of the zonal slot and DRA can be designed independently, which greatly facilitates designs of the dualband CP antenna. The reflection coefficient, AR, radiation pattern, and radiation efficiency of dualband antennas were measured, and the measured results agree reasonably well with our simulated results obtained using Ansoft HFSS.