The invention discloses a feeding network layer and an antenna system. The feeding network layer comprises two feeding networks in mutual mirror symmetry, and each feeding network comprises a feeding input port, a Wilkinson power divider, a slow-wave line structure, aSchiffman phase shifter, and a branch-line directional coupler. The antenna system comprises the feeding network layer, a second dielectric substrate layer, a metal ground layer, a first dielectric substrate layer, and a radiation layer laminated in sequence from bottom to top. The invention also discloses a method for generating four polarization modes of the antenna system, wherein the four polarization modes comprise left-hand circular polarization, right-hand circular polarization, +45-degree linear polarization, and -45-degree linear polarization. According to the feeding network layer, the antenna system, and the method, the design is ingenious, the structure is simple, the defects of unstable structure and high cost caused by realization of the quadri-polarization antenna through change of the physical direction of an antenna oscillator and loading of a radio frequency switch are overcome, and requirements of simple machining of the antenna and easy integration are guaranteed.