High-Isolation Millimeter-Wave Dual-Polarized Patch Antenna Array Utilizing Hybrid Microstrip Line and Substrate-Integrated-Waveguide Series Feeding for Vehicle Radar Systems

This letter presents a millimeter-wave (mmWave) dual-polarized patch antenna array, employing a hybrid series feeding mechanism that combines microstrip line and substrate-integrated-waveguide (SIW) technologies. The array is composed of a microstrip line series-fed patch array, which is stacked atop an SIW series-fed colinear slot array, realized on two substrates. The patch array on the upper substrate is responsible for horizontal polarization (HP) radiation, while the SIW colinear slot array on the lower substrate couples electromagnetic energy to the patch array, producing vertical polarization (VP). Thanks to the feeding scheme, the magnetic symmetry plane of HP is overlapped with the electric symmetry plane of VP, ensuring high isolation between the two polarization ports. Additionally, since both polarizations are radiated from the same patch, their radiation patterns are similar. A 1×6-element array was designed, fabricated, and measured, demonstrating an overlapped -10-dB impedance bandwidth for both polarizations from 23.2 to 24.6 GHz (5.9%). Within this bandwidth, the average gains for both polarizations are approximately 12.5 dBi, with polarization port isolation exceeding 46 dB. The proposed array offers high polarization isolation, low cost, low profile, low cross-polarization, and a simple structure, making it a suitable candidate for implementing dual-polarized 1-D phased arrays in mmWave vehicle radar applications.