Gradient metasurface (GM) can have a pre-defined large wave vector along its sur- face. It has shining attributes as field enhancement and sub-wavelength transmission. In former works, GMs were excited mostly by plane waves illuminated from high above, and experts con- centrated on waveform converting or anomalous reflection. This letter analyses electromagnetic field distribution above GM with some plane waves vertically illuminating. Then it provides a new way to excite GM on one of its edges using parallel plate waveguide, from which we can get an escaping plane wave towards above, and this is the inverse process of plane wave vertical incidence. After a delicate parameter sweep, the simulation shows our design has comparatively high directivity and efficiency within a bandwidth of 0.6 GHz (7.7 GHz to 8.3 GHz). The impact of some important size parameters to the antenna performance is discussed in the letter. On account of the fact that GMs are usually constructed by a mass of unit cells, their shapes are variable and they can cover many facilities, which have great potential in both civil and military use. With the development of metasurfaces, the unit cells will become smaller, and the adjusta- bility of the antennae shapes will rise. To excite GMs with the same unit cells but different shapes, it is possible that we only need to tune their matching structure but not the unit cells. Then a new way to design reconfigurable antennae presents. And with the help of metasurfaces, reconfigurable antennae will be more various and flexible and will have better performance.