Collimating Cylindrical Surface Leaky Waves For Highly Improved Radiation Characteristics Of Holograms

High-resolution microwave leaky-wave holograms excited by a center-fed cylindrical-surface-wave launcher show a null in the object-wave direction, which is an undesired effect for electromagnetic beamforming. Also, planar leaky-wave metasurfaces generating a tilted beam suffer greatly from the destructive effect of nonforward surface leaky waves at frequencies other than the design frequency and they are operable at almost only a single frequency. Here we propose a two-dimensional modified-hologram configuration using a parabolic surface reflector to collimate the nonforward leaky modes into forward leaky modes. The modified hologram exhibits a null-free radiation pattern and greatly increased operating-frequency bandwidth. The consequent frequency bandwidth provides the scannability property by frequency variation. The forward-mode-dominant surface-wave excitation of the hologram allows the metasurface to generate the object beam more precisely; therefore, high directivity over the operating bandwidth is obtained. The concept is verified by fabrication and experimentally tested, confirming beam maintenance over a reasonable frequency range and scannability property. The measurement results are in excellent agreement with full-wave simulation, prove applicable wideband leaky-wave holograms.