Analysis and Design of Filtering Series-Feed Omni-Directional Antenna for V2X Application

In general, the vehicle-to-everything (V2X) series-feed antenna excites the spurious mode radiation in the adjacent bands and thus causes the strong mutual coupling between the vehicle antennas. To solve this problem, this article proposes a method to realize a filtering series-feed V2X antenna. This antenna consists of two radiators connected to a double-sided parallel strip line (DSPSL). The DSPSL operates as the series-feed structure and the first resonator. The radiators function as the second resonator. An equivalent filtering network is analyzed and derived. Then, based on the filter synthesis, the initial design parameters are obtained to realize a second-order bandpass response. However, the synthesis method only involves $S_{11}$ and efficiency ( $S_{21}$ ). The radiation performances are not concerned and satisfied. To solve this problem, the antenna currents are manipulated to generate the taper exciting. Thus, the upper sidelobe and the gain are improved. Moreover, to further enhance the out-of-band suppression level, three radiation zeros are generated by manipulating the current distribution on the DSPSL. The fabrication prototype demonstrates that the out-of-band suppression of the proposed antenna is better than 8.8 dB, which significantly reduces the mutual coupling.