| 摘要 |
A device for measuring vehicle speed by utilizing the Doppler effect includes a microwave oscillator element radiating microwaves to a wave guide, a mixer diode, and a strip line of approximately a Y-shape having two upper portions positioned within the wave guide for receiving the microwaves including both radiated and reflected waves. The two upper branch portions of the strip line are so arranged that both are spaced axially from each other by a distance of a quarter wave length of the microwave existing within the wave guide ( lambda /4), and induce electic power of equal level upon the receipt of the respective radiated and reflected waves. Futher, a first of the two upper branch portions of the strip line is shorter than the other by lambda /4. At a connecting branch portion of the upper branch portions of the strip line, the radiated microwaves, which are received by the two upper branch portions, negate each other to a considerable extent, whereas the reflected microwaves, which are received by the two upper branch portions, positively add to each other. The radiated microwave and the reflected microwave are mixed together at a nearly equal rate and rectified by the mixer diode which is connected to the connecting branch portion of the strip line.
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