Noise and Transmitter Modulation Curve Non-Linearity in the Precision Industrial Short-Range FM Radar

Noise and Transmitter Modulation Curve Non-Linearity in the Precision Industrial Short-Range FM Radar. B.A. Atayants, V.V. Ezerskii, S.M. Smolskiy and B.I. Shakhtarin

Operation peculiarities of the precision FM range-finders on noise background at transmitter non-linear modulation curve (MC) are considered. The evaluation of noise component of the measurement error is fulfilled for small and ultra-small range in devices intended for industrial systems of automatic technological control. The analysis has been carried out for radar devices of small, medium and high measurement accuracy with various complexity extent.

Analytical equations for distance measurement error are given for devices of second and third group with presence of the white normal noise at receiver input. These equations take into consideration in the general case the noise correlation at output of pre-processing device assuming that frequency response is closed to Gaussian form. Effects typical for each above-mentioned group of devices are discussed and some practical recommendations are offered. The detailed quantity estimations of the errors occurred are fulfilled. The possibility of error minimization at noise presence is given allowing the essential increasing of measurement accuracy.

The analysis of measurement accuracy degradation at non-linear MC is performed for simple devices of small accuracy. MC mathematical model is suggested and the method for this model parameter estimation on the basis of measured static characteristic is discussed. Formulas for quantitative evaluation of the error occurred at known MC non-linearity parameters are described, which allow the receiving of these parameters legitimate values for given error level of range measuring.

Methods of error decreasing caused by MC non-linearity are considered. The non-linearity compensation by means of adaptive pre-distortion introduction in modulating voltage is the promising solution together with non-linearity consideration at distance calculation for medium accuracy devices and full elimination of non-linearity influence in high accuracy devices.

For non-linearity compensation two methods are recommended. The first one is based on static MC measurement in the calibration mode and compensating voltage formation on this basis. The second one, which is more promising, is based on the continuous dynamic evaluation of irregularity degree of difference frequency signal in the modulation period and the formation of compensating voltage ensuring the admissible irregularity.

The practical possibilities of formation the signal with linear frequency modulation with the help of digital frequency synthesis.