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Composite right/left-handed (CRLH) transmission line structures based on the folded substrate integrated waveguide (FSIW) are presented and discussed in this paper. This FSIW-based CRLH (FSIW-CRLH) transmission line exhibits much lower cut-off frequencies as compared to the ordinary FSIW of the same footprint, and furthermore, it requires only one-half width of the conventional substrate integrated waveguide (SIW) based CRLH (SIW-CRLH) transmission lines while possessing the same dispersion characteristics. In addition, the proposed structure offers the advantage of a high quality factor for preventing the guided-wave circuits from radiation as suffered in the previous open CRLH transmission line structures when operated in the fast-wave region. All of the aforementioned properties lend the proposed FSIW-based CRLH transmission lines best suited to miniaturized and guided-wave microwave applications. In this paper, a comprehensive study on the FSIW-CRLH transmission structures is conducted by means of its dispersion relation and Bloch impedance. In addition, two partial H-plane filters are implemented here to demonstrate the capabilities of miniaturization and high quality factor based on the proposed FSIW-CRLH structures. The resultant filters are shown to have about 80% size reduction as compared to the conventional FSIW filters, and 59% size reduction as compared to the SIW-CRLH filters. To the best of our knowledge, it is the first time that the partial H-plane filters are implemented utilizing both the dispersion behavior of the CRLH transmission structures and the structural benefits of the FSIW configuration.