Scanning antenna for automobile radar

Abstract

A planar scanning antenna for an automobile radar of 76-77 Hz frequency range has been developed. Antenna operation is based on the transformation of slow surface-mode waves into space ones by periodic scatterers. An electromagnetic method of scanning is used with a fixed antenna aperture. Antenna consists of a planar dielectric waveguide with an excitation unit and diffraction grating. The planar dielectric waveguide of the 120 mm width is excited by the horn-parabolic transition from a hollow metallic waveguide. The waveguide is made of teflon and provides the phase velocity moderation ratio U = 1.17 at the working frequency. A metal disk of 120 mm diameter having a surface covered by the diffraction grating is placed near the surface of the dielectric waveguide. The correct choice of the grating period provides single-beam operating conditions. The disk with the grating is fixed on the axis of an electric drive. The rotation of the disk to an angle a relative to its initial position leads to the deflection of the beam in the horizontal plane to the angle ν = 1.5α. Scanning is realized by continuous rotation of the disk with the grating; thus the frequency of scanning is twice the one of disk rotation. The width of antenna radiation pattern is to 2.2 in the horizontal plane and 2.0 in vertical one with the level of side lobes to be -23 dB and -18 dB, respectively. The working sector of scanning in the horizontal plane ν = -60. While scanning, the width of the radiation pattern in the horizontal plane increased proportionally to 1/cosν. The scanning frequency is equal to 50 Hz at the disk frequency rotation 25 Hz. Total losses do not exceed 1.5 dB. The antenna thickness without motor is equal to 18 mm. It is proposed to use the antenna together with a radar having linear frequency modulation to observe the space before a car in the conditions of poor visibility.