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A novel phase shifter is proposed based on a substrate-integrated-waveguide (SIW) technology. It consists of several phase channels made by SIW resonators loaded with extra metallic posts. These metallic posts act as inductive posts controlling the resonant frequency of the SIW resonators. Circular slots on the upper plate of the SIW structure are used to selectively disconnect these inductive posts from the upper plate of the structure to tune the resonant frequency. It is shown that by properly controlling the resonant frequency in each channel, the phase gradient between adjacent channels exhibits a linear phase progression at the operating frequency. As a result, a novel phase shifter is obtained accordingly. Based on this approach, a phase shifter prototype made by five channels is proposed to validate the concept. Each channel consists of three SIW resonators which form a third-order bandpass filter for impedance matching. Experimental results demonstrate that the resulting phase shifter has more than 10% fractional bandwidth for a 15° phase gradient across adjacent channels with a phase error of ±5°. The insertion loss is less than 1.5 dB in the considered band. The experimental results agree well with full-wave simulations. The proposed phase shifter is expected to be easily implemented with active components.