A pattern reconfigurable antenna for object detection and speed measurement

This paper presents a novel pattern reconfigurable patch antenna designed for object detection and speed sensing in the mmWave band. The antenna features dual-resonance operation, with a primary band dedicated to sensing and a secondary band reserved for auxiliary communication. At the sensing frequency, beam steering in the H-plane is enabled through a reconfigurable structure that integrates an inverted U-shaped copper strip (“cap”) with side cuts, whose state is electronically controlled via a PIN diode. The prototype operates in two distinct bands: 26.9–28.4 GHz for sensing, and 30.6–31.8 GHz for a secondary communication function. At the sensing frequency, the antenna beam can be steered to three distinct directions (−33°, 0°, and 33°), enabling spatial coverage for object tracking and speed estimation. The antenna characterization results show a peak gain of 5 dBi, maximum efficiency of 66%, and impedance bandwidth of 4%–5.4%, depending on the bias state. The antenna's sensing performance is validated through two experimental scenarios: (1) the detection and localization of a metallic object placed in front of the antenna, and (2) speed estimation of a moving waveguide antenna. The antenna was able to detect the speed of the antenna moving with velocities ranging from 2 to 25 mm/s with a measurement uncertainty of less than 1.2%. These results demonstrate the antenna's capability as a compact and effective mmWave sensor for integrated object detection and velocity estimation in advanced sensing applications.