Spatial Fourier transform method of measuring reflection coefficients at oblique incidence. I: Theory and numerical examples

A new method using spatial Fourier transform has been developed to measure reflection coefficients at oblique incidence. The method involves the measurement of complex pressure distributions on two parallel planes lying close to the surface of a test material and decomposing each of the complex pressure distributions into plane-wave components by using two-dimensional spatial Fourier transform. The incident and reflected plane-wave components on the surface of the test material can be mathematically separated by the use of plane-wave propagation theory. This separation leads to the determination of reflection coefficients at arbitrary angles of incidence. Investigation has been made into the error due to the finite size of the measurement area to show that the magnitude of the error can be reduced by using a dipole source instead of a monopole source. Numerical examples are given to illustrate the validity of the method.