Reflection-less Lens Based on Miniaturized-Element Frequency Selective Surfaces at Millimeter-Wave Frequency Range

A reflection-less lens antenna based on miniaturized element frequency selective surfaces (MEFSS) arranged in a quasi-periodic structure is investigated to provide not only a collimated beam but also a very low reflection towards its feed. This antenna is a key component in a sensitive, high resolution instrumentation polarimetric radar designed for phenomenological radar studies of traffic scenes in the 77 GHz band. The incident wave phase correction is accomplished locally on the surface of the lens through a spatial filter that makes use of only shunt elements. To achieve 0-360⁰ phase shift, the lens includes three MEFSS layers using gold deposited on top, bottom, and in the middle of two glass wafers. As an air-gap between the glass wafers can affect the performance significantly, very smooth glass wafers are fused in a high temperature furnace after patterning the MEFSS layers with careful alignment. The lens has F/D~2 and is fed by a dual-polarized horn antenna with 7 dB field drop at the edges.