A dual and triple band bandpass filter is designed operating at X and Ku-band. Based on pure geometric analysis of width to length ratio's relationship with modes generated in substrate integrated waveguide cavity, a square substrate integrated waveguide cavity is designed to operate at TE101, TE201, TE102 modes. Coupling matrix for passband is derived based on coupling topology from the resonating nodes, with the center frequency of 10.5GHz, 15.5GHz, 17.5GHz for the first, second and third passband. The modes excited in a cavity with variation of different feeding positions is analyzed. Two identical square cavities are magnetically coupled together to get triple passband response and it was found that theoretical and simulated results are in good agreement with each other. © 2017 IEEE.