A Miniaturized Planar Multibeam Antenna for Millimeter-Wave Vehicular Communication

Existing millimeter-wave beamforming network-based multibeam antennas usually suffer from complex configuration and bulky size, which limit their applications on a vehicle. To address these issues, in this paper, a symmetrical series-fed array topology is proposed for eliminating the conventional beamforming network. The topology is constructed by applying two unequal main transmission lines (TLs) to symmetrically feed a linear antenna array in series. To effectively suppress the mutual coupling between two TLs, an antenna element exhibiting co-polarized in-band full-duplex performance is implemented. When the four terminals are excited, respectively, four groups of excitation signals with different phase differences will be delivered to antennas to implement the desired beam steering characteristics. For validation, an antenna array operating at 28 GHz is designed, fabricated, and measured. Thanks to the simplicity of topology, the overall size of the proposed multibeam antenna is only 5.57λ² with a radiation efficiency of 85.6%. Meanwhile, a comparable performance is obtained when compared to a conventional beamforming network-based multibeam antenna. All of these results demonstrate the potential of the proposed topology in miniaturized millimeter-wave vehicular communication.