Surface Plasmon Polaritons (SPPs) have been attracting the interest of microwave technology researchers recently because of the the property of near-field enhancement. In this paper, firstly, we discuss the existence of SPPs in the surface of metal in microwave regime. We also analysis the motivation of SPPs. Secondly, we introduce a high gain slot antenna with single-layer director briefly. Thirdly, a four-layered slot antenna with compact size and high gain is proposed. This antenna is based on the previous antenna. The difference between them is that a dielectric grid structure is added to the last one. The dielectric grid structure makes the incident electromagnetic wave scattered, which makes the wave vector of the incident electromagnetic matched with the surface plasmon polaritons in horizontal direction, so that the incident electromagnetic wave can couple with SPPs. The simulated gain of the previous antenna is 12.0 dBi at 5.6 GHz and measured gain is 10.4 dBi at 5.57 GHz. The simulated gain of the last antenna is 13.5 dBi at 5.6 GHz and measured gain is 11.4 dBi at 5.57 GHz. The 2 dBi dropped for the measured and simulated gain can be caused by the loss of dielectric. By motivating SPPs, the simulated and measured gain of the antenna enhances nearly 1.5 dBi and 1 dBi separately. The overall size of both the antenna is 100 × 100 × 19 mm3 .