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The development of innovative terahertz (THz) imaging systems has recently moved in the focus of scientific efforts due to the ability to screen substances through textiles or plastics. The invention of THz imaging systems with high spatial resolution is of increasing interest for applications in the realms of quality control, spectroscopy in dusty environment and security inspections. To realize compact THz imaging systems with high spatial resolution it is necessary to develop lenses of minimized thickness that still allow one to focus THz radiation to small spot diameters with low optical aberrations. In addition, it would be desirable if the lenses offered adaptive control of their optical properties to optimize the performance of the imaging systems in the context of different applications. Here we present the design, fabrication and the measurement of the optical properties of spectrally broadband metamaterial-based gradient …