Electromagnetic theory of wire-grid lens HF antennas

The Wire-Grid Lens Antenna is a unique realization of the Luneburg lens technique for frequencies in and near the HF frequency band. An effective refractive index which varies from the
\sqrt{2}
at the lens center to a value near unity at the lens edge, is attained by two layers of square-mesh wire grid positioned one above the other. [1],[2] At the center of the lens, the two grids are spaced close together; and at lens edge, the grids are spaced far apart compared to the mesh size of the grid. This paper presents the electromagnetic analysis of the wave propagation within the lens and of the radiation from the lens leading to the calculation of the radiation pattern of the lens. A typical Wire-Grid Lens Antenna is shown in Fig. 1. The inner circle is the lens proper; a flared horn is attached to the lens to provide an impedance match between the lens and free space.