In this paper, we report an interferometric method to extract the phase information available in a desired band of spatial frequencies. The phase sample is placed in the path of a converging beam of light entering a Mach Zehnder interferometer so that the two Fourier Transform (FT) planes are located in the two interferometer arms. One of the FT planes is filtered by suitable masks so that only the frequencies that are blocked appears in the final interferogram. An imaging lens images the phase object on a CCD. Polarization Phase Shifting is incorporated so that the final frequency filtered image is reconstructed from the four phase shifted interferograms. The interferometer is made to operate in null fringe condition so that residual phase is eliminated. Simulated and experimental results are presented.