Abstract: Based on analyzing the dispersion characteristics and the global band gaps for general two-dimensional photonic band gap structures formed by triangular arrays of metal posts, we select TE04 at 140 GHz as the operational mode and present the modes distribution diagram in different band gaps. By optimizing the operational point, the number of modes competing with TE04 reduces from 5 to 2. On the other hand, the lattice constant and the radius of metal columns are expanded, thus it can bear more thermal loading. Finally, comparisons are made between electric field distributions of TE04 in different band gaps.