Ultrabroadband compact lens antenna with high performance based on a transmission gradient index medium

A gradient refractive index design strategy is proposed for a flat lens, which can transform a wavefront by rectifying the local transmission phase. The designed lens is composed of two types of low-loss dielectrics with subwavelength gradient periodic structure and manufactured by 3D printing and computer controlled machining. The measured results of the near and far field agree well with those of theoretical predictions and numerical simulations. It is demonstrated that this light-weight, low cost, compact lens antenna is highly directive (side lobes below -10 dB) and the incident plane waves are focused well with high focusing efficiency (above 80%) over an ultrabroadband frequency range with a bandwidth ratio of 138% (4-22 GHz). The demonstrated flat lens provides an alternative strategy for microwave communication, detection, and imaging applications.