In this paper, we first propose a metamaterial structure by etching the same two interdigital fingers on the upper ground of quarter mode substrate integrated waveguide(QMSIW). The simulated results show that the proposed QMSIWbased metamaterial has a continuous phase constant changing from negative to positive values within its passband. A periodic leaky-wave antenna(LWA), which consists of 11 QMSIW-based metamaterial unit cells, is designed, fabricated,and measured. The measured results show that the fabricated antenna achieves a continuous beam scanning property from backward-43° to forward +32° over an operating frequencyrange of 8.9 GHz–11.8 GHz with return loss better than 10 d B.The measured antenna gain keeps consistent with the variation of less than 2 d B over the operating frequency range with a maximum gain of 12 d B. Besides, the measured and simulated results are in good agreement with each other, indicating the significance and effectiveness of this method. In this paper, we first propose a metamaterial structure by etching the same two interdigital fingers on the upper ground of quarter mode substrate integrated waveguide (QMSIW). The simulated results show that the proposed QMSIWbased metamaterial has a continuous phase constant changing from negative to positive A periodic leaky-wave antenna (LWA), which consists of 11 QMSIW-based metamaterial unit cells, is designed, fabricated, and measured. The measured results show that the fabricated antenna achieves a continuous beam scanning property from backward -43 ° to forward + 32 ° over an operating frequency range of 8.9 GHz-11.8 GHz with return loss better than 10 d B. The measured antenna gain keeps consistent with the variation of less than 2 d B over the operating frequency range with a maximum gain of 12 d B. Besides, the measured and simulated results are in good agreement with each other, indicating the significance and effectiveness of this method.