Substrate Integrated Waveguide (SIW) has been widely used in the design of microwave circuits and systems due to its low insertion loss and high-quality factor. However, compared to traditional microstrip lines, SIW has larger transverse dimensions, which limits its application in miniaturized and compact microwave circuits and systems. This paper proposes a SIW-SSPP hybrid circuit by integrating a three-dimensional SSPP structure composed of metallized blind vias and metal patches. Theoretical analysis of dispersion characteristics and full-wave electromagnetic simulations demonstrate that this SIW-SSPP integrated hybrid circuit can achieve a 30% reduction in transverse length and a 50% reduction in longitudinal length of the transmission line. Furthermore, by etching an orthogonal radiation structure on top of the SIW-SSPP hybrid circuit, a compact ultra-wideband circularly polarized leaky-wave antenna was designed. The results indicate that the antenna exhibits a return loss below -10 dB and an S₂₁ below -6 dB within the operating frequency band of 11.2 to 17 GHz. It achieves an axial ratio of less than 3 dB between 11.2 and 16.2 GHz. The antenna's gain ranges from 10 to 15 dBic. It also features continuous scanning performance from backward space (-27°) to forward space (+30°). This design method provides a new approach for the development and design of high-performance, compact microwave, millimeter-wave, and terahertz systems.