Synthetic Aperture Radar (SAR) image processing involves a two dimensional (2-D) Fourier Transform (FT) and the spectrum shape introduces high intensity sidelobes. These sidelobes may severely distort the image. Apodization technique can decrease the sidelobes level while preserving the image resolution. However, in Ultra wideband (UWB) SAR imaging, we have to reduce both orthogonal and non-orthogonal sidelobes. In this paper, a new linear window function has been presented based on analysis of different linear and non-linear apodization techniques. This new linear method controls both orthogonal and non-orthogonal sidelobes better than other conventional window functions. This method has been applied and verified with a real SAR image.