An antenna is provided for GNSS and other applications and includes an adjustable-height vertical support PCB mounted on a ground plane and mounting a crossed-dipole radiating arm element assembly. The gain pattern of the antenna can be varied by constructing the vertical support PCB with different heights or adjusting the height and gain pattern in the field. Vehicles with significant pitch and roll can be provided with low-horizon tracking capability by providing a high-profile antenna configuration. Alternatively, low-profile configurations provide steeper gain pattern rolloff at the horizon for maximal multipath rejection and high accuracy. The droop angles of the radiating arm elements are also adjustable for varying the gain pattern and beamwidth. A matching and phasing network is connected to the radiating arm elements and provides a relatively constant input impedance for the various antenna configurations. Alternative aspects of the invention have different configurations of the radiating arm elements and ground planes.