A low-profile aperture impedance matching technique for TEM planar Luneberg lens

A novel low-profile aperture impedance matching technique of TEM Luneberg lens is presented. The trapezoidal strips at the edge of the lens is the impedance matching transition from the lens to the free space. In order to verify this method, a TEM mode Luneberg lens antenna over the 60-61 GHz at V-band is manufactured by using metamaterial surfaces. The refractive index of the lens is extracted by the novel S-parameter retrieval method. An inverted L probe antenna is used as the feeding structure which can excitate the TEM mode electromagnitic wave between the metal plate and the metamaterial surface, and this architecture is easy to produce. The matching structure improved the SLL (sidelobe level) with a 2 dB drop, so the far-field radiation pattern operates a good performance around the desired frequency band, which verified the validity of the aperture impedance matching technique.