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International Journal of Antennas and Propagation
Volume 2012 (2012), Article ID 492326, 9 pages
Research Article

Antenna Beamwidths of Above-The-Road Radar for Traffic Speed Enforcement in China

Division of Mechanics and Acoustics, National Institute of Metrology, Beijing 100013, China

Received 26 March 2012; Revised 2 June 2012; Accepted 12 June 2012

Academic Editor: Charles Bunting

Copyright © 2012 Lei Du et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Above-The-Road (AbTR) radar is a new type of speed measurement device used in China for traffic speed enforcement. The antenna beamwidths in vertical and horizontal directions are critical parameters for AbTR radar because speed measurement accuracy partly depends on vertical beamwidth and speed measurement interference from adjacent lanes can be effectively minimized by appropriate choice of horizontal beamwidth. In this paper, the speed measurement principle of AbTR radar is introduced and the reason for field speed measurement error is presented. The speed measurement error is theoretically calculated in various combinations of different vertical beamwidths and possible installation angles. The requirement for horizontal beamwidth to operate with less interference from adjacent lanes is also theoretically laid down with different installation heights and angles. Field tests with three equal-distanced piezosensors each lane as triggering references have been performed on an AbTR radar sample with vertical beamwidth 5.1° and horizontal beamwidth 5.2°. The results of theoretical analysis and field tests validate that the requirement of less than 6° for AbTR radar antenna beamwidths in vertical and horizontal directions is a precondition for accurate and reliable field measurements, which has been added to the China’s pattern approval regulation for AbTR radar devices newly published.