Abstract
This paper describes the method of decreasing the inherent error, the so-called step error, in a conventional FM-CW radar. In this method the microwave antenna is driven to the amount of nλ/4. in order to modulate the phase of microwave, where λ is the wavelength of the carrier wave and n is an integer. During the modulation, the step error is averaged and then decreased.
The maximum phase deviation in this method is always equal to nπ, independent of the distance to be measured, which is the condition that minimizes the step error. First, the properties of the residual error is analized for the case when a stroke of the antenna deviates from nλ/4.
Next, a distance is experimentally measured with the radar in order to confirm the decrease in the step error. As a result of these experiments, it is found that when the maximum frequency deviation is 100MHz, the standard deviation of residual error is less than 30mm, though the step error in a conventional FM radar would be 37.5cm.
Moreover it is found that this radar can be used to measure from such a short distance as 0.5m.
Taking advantage of these merits, this method can be adapted to the level meter of coke or ore in the blast furnace, to the level meter of molten steel in the converter and to some other cases of industrial use.
