Classical corrugated waveguide (WG) LP filters with wide rejection bandwidths rely on designing a band stop block with reduced height waveguides augmented by impedance matching blocks at terminations. In this paper direct synthesis approach is used to synthesize the whole filter as a single unit. The initial filter is designed as a TEM mode commensurate length LPF with very high quarter wavelength frequency for size reduction. Filter is made up of series SC stubs interlaced by contributing Unit Elements (UE). Then the filter is converted into its WG equivalent. The finite transmission zeros formed by the SC stubs are spread into the stopband properly to get both steep skirt and high rejection level. Return loss and rejection level is then adjusted by manual tuning of stub lengths and heights of UE's. The resulting filter is then optimized on electromagnetic simulators. A Ku-band filter is designed and implemented as example.