In this paper, a design method for multiband bandpass filters with compact configuration in substrate integrated waveguide is proposed by combining the single-band/dual-band synthesis method and the multimode resonator theory. The designed filters could generate multiple filtering passbands without expanding their entire physical size. In addition, all the passbands could be efficiently synthesized and designed with any prescribed order in theory, which has been rarely reported in multiband filters, especially in the design of quad-band filters. As examples, one third-order quad-band filter and one third-order tri-band filter are designed, fabricated, and measured. Good agreement is attained between their simulated and measured S-parameters, and both the two sets of results have verified the feasibility of the proposed design method and attractive performances of the designed multiband filters.