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A uniform ferrite-loaded open waveguide structure with composite right/left-handed (CRLH) response and its application to a novel backfire-to-endfire leaky-wave antenna are presented. The structure consists of a ferrite-filled rectangular waveguide open to free space at one of its small sides and biased perpendicularly to its large sides. Based on the fact that the leakage from the open side represents only a small perturbation in terms of guidance, an analytical dispersion relation for the approximately equivalent perfect magnetic conductor closed waveguide structure is derived. The unique dispersive properties of this structure, including its inherent CRLH balanced response (gapless nonzero group velocity transition between the left- and right-handed bands) and low-loss characteristics due to off-resonance operation, are extensively described, parametrically studied, and concretized by design guidelines. This theory is validated by both finite-element method and finite integration technique full-wave results and demonstrated experimentally. The leakage of the structure is exploited to build a full-space backfire-to-endfire scanning leaky-wave antenna, which is capable of both fixed-bias frequency scanning and fixed-frequency bias scanning, while being a perfectly uniform structure not requiring any chip tuning components. This feature, and its subsequent design simplicity, represents a fundamental advantage over previous CRLH metmaterial implementations. To the best of our knowledge, the proposed ferrite waveguide is the first and unique uniform structure exhibiting a CRLH response.