An antenna system for a global navigation satellite system reference base station is disclosed. The antenna system includes an antenna positioned above a high capacitive impedance surface (HCIS) ground plane. Over a specific range of the lateral dimension of the HCIS ground plane and the height of the antenna above the HCIS ground plane, a high level of multipath suppression and high sensitivity for low-elevated satellites can be simultaneously maintained. The HCIS ground plane can be fabricated as a flat conducting plate with an array of conducting elements such as pins, pins with expanded tips, or mushroom structures. Alternatively, the HCIS can be fabricated as a flat conducting plate with a concentric series of choke rings. The antenna system can provide a positioning accuracy of +/-1 mm, an order of magnitude improvement over previous designs.