A cross-slot-coupled dual-band circularly polarized rectangular dielectric resonator antenna (RDRA) with a small frequency ratio (1.23) based on compass navigation satellite system (CNSS) applications is designed, fabricated, and measured. The RDRA is excited to resonate at two pairs of near-degenerate orthogonal modes of TE111 and TE113, and a cross slot is introduced to simultaneously achieve dual-band right-hand circular polarization. The measured -10 dB impedance bandwidths of 11.4% and 8.4%, 3-dB axial ratio (AR) bandwidths of 2.1% and 2.2%, and antenna gains of over 5.4 and 4.3 dBic are obtained for CNSS B3 and B1 bands, respectively. Reasonable consistency is achieved between measured and simulated results of reflection coefficients, ARs, and radiation patterns.

A flat Luneburg lens antenna for Ku-band (12—18 GHz) applications is proposed and designed using ceramic 3-D printing. Metamaterial structures and transformation optics technology are used to realize the gradient dielectric constant, compress the height, and reduce the weight of the Luneburg lens. The proposed 3-D printed Luneburg lens, combined with a 10-dB standard gain horn antenna, obtained an antenna gain up to 19.1 dBi over the operating frequency and the thickness reduction of 78%. In addition, the ability of the flat Luneburg lens to perform passive beam scanning with limited power loss is achieved. This exploration of ceramic 3-D printing can serve as reference for the development of ceramic components with complex structures.