Modeling Of Multipath Propagation And Elimination Of Angle Measurement Error Based On Monopulse Angle Measurement

Radar is affected by multipath propagation when detecting low elevation targets.The reflected signal and the direct signal enter the main antenna beam at the same time,which makes the radar angle measurement deviation and leads to the reducing of the detection precision of the target angle and which greatly affects the tracking and interception of the low altitude penetration target.When the multipath effect is serious,it will cause the loss of the target.How to eliminate the multipath effect or reduce the influence of multipath effect on angle measurement is one of the most important issues in radar field.This paper starts from the viewpoint of radio wave propagation.The mechanism of monopulse angle error caused by multipath propagation is discussed and the method of angle error elimination is explored.The skeleton of this paper as follows.Firstly,the electromagnetic characteristics of radio propagation environment and topography and geomorphology are introduced.The propagation mechanism of multipath and the propagation mode of multipath are studied.The multipath propagation modes include reflection propagation mode,diffraction propagation mode,transmission propagation mode and scattering propagation mode.According to the judgment standard of terrain irregularity,this paper mainly studied the reflection propagation mode.The calculation formulas of the reflection coefficients of different terrain are derived.The influence of different grazing angles on the reflection coefficient is simulated.Emphatically study on the effect of multipath reflection on the received signal.According to the superposition of multipath theory,deduce the calculation formula of receiving field.For example,the effect of plane reflection on receiving signals.Secondly,the basic principle of monopulse radar is summarized.Two basic angle measuring methods and four common angle measuring methods of monopulse radar are introduced.Based on the above research,the single pulse amplitude and differential angle measurement is mainly introduced,and the influence of multipath propagation on the amplitude and difference angle of monopulse is analyzed.Finally,based on the theory of radio propagation and the principle of monopulse amplitude difference method.The numerator and denominator in the formula of radar angle measurement error respectively for synthetic and differential voltage error function and differential voltage error function.Analysis of the effect of the radar carrier frequency,the form of the electromagnetic wave polarization,the dielectric constant,the grazing angle and the roughness of multipath and difference voltage error.From the above analysis,we can draw a conclusion that the electromagnetic wave polarization,dielectric constant and the effect of roughness on the influence and difference voltage error.With the analysis of the angle measurement error under the influence of the multipath,put forward the research idea of the influence factors analysis of the difference voltage error and the three level angle measurement error cancellation method is proposed.That is geometric elimination,phase cancellation and synthetic and differential voltage error cancellation.According to the number of known conditions,we choose different cancellation methods to eliminate the angle error under multipath effect.The method of geometry elimination is based on the relationship between the radar and the target to a rough estimate of measurement error.The method of phase elimination is based on the path difference caused by the phase difference to attain eliminate the error of the angle.However,to purpose of achieving elimination error based on the method of synthetic and differential voltage error cancellation,which makes the angle measurement error greatly reduced.For the three level cancellation method,which can be used independently,but also can complement each other.When using these three methods to the measurement error for the mean value at the same time.On the receiving device plus or minus the error angle to avoid the influence of multipath angle.