DEVICE FOR MEASURING CAR SPEED BY DOPPLER RADAR

摘要

PURPOSE:To reduce radio interference of a Doppler radar for measuring an absolute speed of a car with a simple configuration by setting up a radio shielding plate on a position where a vertical surface including the main beam of a horn antenna is intersected with the under surface of a floor. CONSTITUTION:A radio shielding plate 6 is set up on a position where the plate 6 is intersected with the vertical surface including the main beam under the floor of a car on the side that an angle formed by the main beam 2 of the horn antenna 1' and the horizontal direction is <=90 deg. and a horizotal beam 3 out of the subbeam which is a side loop from the horn antenna 1' is prevented from being irradiated to the external. Beam penetration from the external to the horn antenna 1' is prevented and the main beam 2 is reflected by the ground 5 and the lower surface of the floor and leaked to the outside of the car by repeating direct reflection, but is attenuated because of the repeated reflection, so that no trouble is generated. When the shielding plate is formed by a radio reflecting material, the horizontal beam 3 is reflected and a part of it is returned to the shielding plate, but the detection of Doppler frequency is not influenced because the relative speed of the horn antenna 1' and the shielding plate is ''0''.