Abstract: In this paper, traditional ultra-wideband stub filters are modified to have more transmission zeros with optimized distribution to achieve sharp rejection slope at the high edge of passband. Firstly, the short-circuited stubs are set to have different lengths and the corresponding transmission zeros are no longer fixed at 2f₀, but distributed optimally. Secondly, every 1/4λ connecting line is loaded with an open-circuited stub of certain length to introduce one transmission zero. The design of a three-order filter is conducted by optimization. The measured responses have well validated the feasibility of the methods.