On the basis of the theory of electromagnetic test the paper researchs a new electromagnetic testing method which is not only fit for testing the distance of stretch out and draw back of the piston rod of hydraulic support working under the mining pit but also for the linear constants of the mechanical equipments working on the groun

For the fast-moving target,range dispersion will occur in the DFT range compression,deriving from the high-speed radial motion,distort the range profile and defocus the ISAR image.