Dual-feed hybrid antenna with low isolation and cross polarization

Abstract

The experimental return loss results for the proposed antenna is depicted in Fig. 2, showing both feeding mechanisms are resonated at around 2.4 GHz with an operating bandwidth of 350 MHz. As for the aperture coupled feed at port 1, the circumference of the annular ring slot is designated to excite a full-wavelength resonant mode centered at 2.415 GHz, and its broad impedance bandwidth (14.5 %) is due to a combination of the resonant modes of the coupling slot and the radiating patch. The isolation between the two feeding ports for the proposed antenna is also presented in Fig. 2. In this figure, an isolation of less than-40 dB over the entire operating bandwidth is measured. Note that such isolation value is not commonly reported in the open literature especially for a dualfeed dual-polarized antenna design. The achievement in this case is most probably due to the two very different feeding mechanisms that aids in achieving good decoupling between the two feeding probes. Fig. 2 also presented the variation of the XPL measured at the z-axis (on-axis XPL, E(θ = 0°) crosspol / E(θ = 0°) copol ) against frequency. From the experiment, it is noteworthy to learn that by fine tuning the protruded length l s at both open end of the T-shaped coupling strip, a peak XPL (sharp notch) that possesses good polarization purity can be achieved within the 350 MHz impedance bandwidth. In this study, a peak XPL of around-40 dB is measured at 2.4 GHz, which is slightly different from the center frequency of the proposed antenna measured at both feeding ports. By measuring the off-axis XPL at this frequency, port 1 demonstrated a XPL between−26 to−30 dB at both principal planes (E- and H-plane), while port 2 shows a level between−21 to−26 dB.