A Wideband 4×4 Patch Array Antenna With Low Sidelobes for Radar-Based Obstacle Detection in Railway Transportation

This paper presents the design, fabrication, and measurement of a $4\times 4$ patch array antenna for radar-based obstacle detection systems in railway transportation. Sidelobe suppression is achieved through amplitude tapering of sub-array elements in the E-plane and asymmetric power dividers in the feed network for the H-plane. The array antenna is framed by a coplanar ground conductor to further reduce sidelobes and fed by a coplanar waveguide port for enhanced impedance bandwidth. The proposed antenna offers an impedance bandwidth from 9.13 GHz to 9.76 GHz (6.3%) and a broadside gain of 18.15 dBi at the center frequency of 9.55 GHz. Sidelobe suppression exceeds 12.22 dB and 19.06 dB in the E- and H-plane, respectively. The 3-dB beamwidth is 17° in the E-plane and 16° in the H-plane with simulated radiation efficiency of 85%. A prototype was fabricated and measured, with sensitivity analysis conducted to assess performance variations due to fabrication tolerances and measurement fixture effects. To validate system performance, antenna prototypes were integrated into a frequency-modulated continuous wave radar system and tested in a realistic railway environment. The system successfully detected a truck crossing a railway track at approximately 1,260 meters, confirming the antenna’s suitability for radar-based obstacle detection in railway transportation.