24-GHz Focused Beam 2 × 2 Patch Array with Coupling Strip for In-vehicle Surveillance

A focused beam 2×2 patch array is proposed and demonstrated for in-vehicle vital sign signal surveillance systems at 24 GHz. The design goal is to overcome the undesired defocusing effects caused by radome due to diffraction. To tackle the problem, a parasitic coupling strip is inserted between the pair of series-fed patch arrays. By properly controlling the length of conducting strip, the radiation from open ends of patches and coupling strips are added in phase to boost the peak gain at the zenithal direction. It thereby re-focuses the beam and alleviates EM wave leakage through windows of a vehicle. The design concept is illustrated in terms of parametric study and explained by simulated current distribution. In addition to S-parameters, radiation patterns are measured in terms of the normalized EIRP patterns taken from a fully-integrated active module for better approximating the real scenario. The experimental results clearly support the design concept.