Commercial micro wave Doppler radar is installed on agricultural tractor ground speed sensor, because the slippage of the tractor wheels does not affect the speed measured by the sensor. The travel distance is calculated from the ground speed, and the farm work monitoring system has been developed for the agricultural tractor. To improve the performance of the Doppler radar ground speed sensor at low speed, it is very effective to shorten the wave length of the radar. The lowest speed that is able to measured by the micro wave Doppler radar ground speed sensor may be 1m/s, because the wave length of the micro wave is larger than or equal to 10mm. The length of millimeter wave is between 10mm and 1mm, so it will be able to measure lower ground speed than by the micro wave Doppler radar ground speed sensor. The millimeter wave Doppler radar ground speed sensor will be performed better than the micro wave Doppler radar ground speed sensor because of shorter wave length, and it may be good for the lower speed vehicles. The millimeter wave Doppler radar ground speed sensor was evaluated in this work to evaluate it as the low speed off-road vehicle. Measured frequency of the millimeter wave Doppler radar sensor was about 47Hz at 0.1 m/s. The relation between the travel speed measured by the wave Doppler radar ground speed sensor and the vehicle speed showed good accuracy in the belt speed test and the indoor soil bin test at lower speed than 1 m/s. Results of the work showed that the millimeter wave Doppler radar is suitable for the low speed off-road vehicle such as agricultural tractors.
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