Sidelobes degrade radar performance by placing energy up and down range from its source. Range sidelobes associated with a large radar cross section (RCS) target may mask the presence of a smaller target located within a pulse width of the larger target; thus, “low" sidelobes are a desirable property. All the synthetic aperture radar (SAR) Sidelobe reduction algorithms which using matched filtering (windowing) like hamming window reduce the sidelobes on the expense of degrading the resolution. Our proposed algorithm using an optimum filter is reduced the sidelobes in range direction while
keeping range resolution. In this paper, drive the formula for filter that reduce the sidelobe after linear frequency modulation matched filter then check the ambiguity function for proposed filter. Finally applied simulated and real raw data of SAR to proposal algorithm for SAR image formation and range Doppler algorithm and measure the quality of focused image.