Frequency-dependent dielectric properties of 3-D-printed structured dielectrics (dielectric crystals) with engineered effective permittivity for micro-and mmWave applications are studied. Different modeling and measurement techniques for broadband dielectric properties of such 3-D-printed crystals are reviewed, their tradeoffs discussed, and individual results compared. Numerically obtained results from the plane wave expansion method (PWEM) and Floquet port scattering are compared with traveling-wave measurements in both guided and free-space setups. Furthermore, the shortcomings of effective media theories (EMTs) and resonance measurement methods are addressed and contrasted against broadband methods. Individual simulation and measurement setups are reviewed with respect to dielectric crystals with simple cubic (SC) and face-centered cubic (FCC) symmetry, with different unit cell sizes and volumetric infill fractions. Extracted effective permittivity values from PWEM and Floquet port simulations show excellent agreement with traveling-wave measurements in both guided and free-space scenarios. Furthermore, the discussed broadband methods predict and measure frequency-dependent effects that are not covered by EMTs and resonance measurement setups, highlighting the necessity to adopt more sophisticated simulation tools for the design of graded-index devices. It is shown that the effective media bandwidth of dielectric crystals depends on the respective unit cell symmetry and that FCC symmetry obtains a significantly increased bandwidth compared with SC symmetry.

In state-of-the-art frequency-modulated continuous-wave (FMCW) multiple-input multiple-output (MIMO) radar systems, antennas are usually designed based on microstrip technology. They are arranged in uniform arrays such that the synthesized virtual array maximizes the angular resolution. This paper presents the design of a 77-GHz FMCW MIMO radar frontend with antennas and feed structures based on substrate integrated waveguides (SIW) and non-uniform planar arrays optimized for sidelobe suppression. A design procedure for MIMO arrays with particular emphasis on sidelobe level suppression based on convex optimization is presented, and a novel transition from differential microstrip line to SIW is utilized to feed the transmit antennas. Measurements show the successful SIW and antenna design, as well as a sidelobe level of 40 dB within the field of view (FOV) of the radar system.