MILLIMETER-WAVE PLANAR ANTENNA

PROBLEM TO BE SOLVED: To solve the problems that it is necessary for a redome to be provided for preventing an antenna from collisions with obstacles such as wind, rain and small stones accompanied with running of a vehicle, wherein the thickness of the redome for low frequencies is smaller in comparison with the wavelength, but the thickness seriously affects and becomes approximately the same size as the wavelength for EHFs, when the redome is placed in front of the antenna, the electric waves radiated from the antenna are attenuated by the redome, multiplexed reflection is occurred due to reflection of multiplexed reflection, and radiative efficiency is reduced and disturbance of excitation distributions are occurred, so that influences such as rise of side lobes and cross polarization being exerted, as a result, misdeterminations about spacing between cars occur and correct measurements about the spacing become impossible. SOLUTION: A millimeter-wave planar antenna comprises a function for adjusting intervals between the antenna and the redome and determines a thickness of the redome as an integral multiple of approximately half the wavelength. COPYRIGHT: (C)2003,JPO