All-dielectric, true-time-delay, planar microwave lenses

We present a new technique for designing planar microwave lenses with broadband, true-time-delay response types. The lenses examined in this work are planar structures with circular apertures populated with numerous spatial time-delay units (TDUs). Each TDU is the unit cell of an appropriately designed lowpass frequency selective surface (FSS) that provides a desired time delay over a wide frequency range. The lowpass FSSs used in this paper are all-dielectric type multi-layer structures that are composed of high-ε_r and low-ε_r dielectric substrates cascaded sequentially. An all-dielectric lens prototype with focal length to aperture diameter ratios (f=D) of 1.3 is designed, fabricated, and experimentally characterized. It is experimentally demonstrated that the fabricated lens can operate over a bandwidth of 40% without any chromatic aberrations. Moreover, the proposed lens demonstrates an excellent scanning performance with fields of views of ±60°.