Lightweight diamond-lattice Luneburg lens supports full polarization for X-band multibeam systems

Researchers from Southeast University, City University of Hong Kong and Purple Mountain Laboratories have detailed a new three-dimensional printed Luneburg lens (LL) antenna built around diamond crystal lattice architecture, published in Engineering. The work presents the first full-polarized spherical LL constructed with diamond lattice unit cells, addressing persistent drawbacks of conventional cubic lattice LL designs while retaining core beamforming performance of traditional full-scale gradient-index (GRIN) Luneburg lenses.

Multibeam antennas relying on lens-based passive beamforming are widely deployed in satellite communications, radar sensing and microwave imaging, yet existing 3D-printed LL unit cell structures such as dielectric posts, slabs and simple cubic lattices carry notable limitations. Many asymmetric unit cells deliver inconsistent effective permittivity under varying incident angles and polarization states, failing to simultaneously stabilize linear and circular polarization radiation across wide bandwidths. Simple cubic lattice LLs also feature a 52% spatial occupancy rate that creates excess mass, while asymmetric cell geometries restrict uniform wide-angle scanning across both elevation and azimuth planes. Diamond crystal lattices, by contrast, adopt tetrahedral covalent bonding between unit elements with only 34% spatial packing density, paired with strong structural isotropy that minimizes permittivity fluctuation under varied wave incidence.

The research team adopted photopolymer VeroClear as the base printing material with a fixed permittivity of 2.9 and loss tangent of 0.01, extracting unit cell effective permittivity via S-parameter retrieval methods to match the radial refractive index distribution defined for ideal spherical Luneburg lenses. The full spherical lens was discretized by mirroring an eighth-sphere segment divided into ten graded layers, where each layer tunes the polymer cube dimension inside diamond lattice unit cells to produce a continuous gradient permittivity profile ranging from 2.0 at the lens core down to 1.1 at the outer surface. Comparative characterization across four common lattice topologies confirmed diamond lattice cells hold the lowest effective permittivity variance across 0° to 90° incident angles relative to post, simple cubic and body-centered cubic lattice alternatives.

To enable full polarization operation, the team engineered a broadband sextuple-polarized feeding system combining a quadruple-ridged dual-polarized horn antenna and a multi-section Wilkinson power divider feeding network integrated with loaded-stub 90° and 180° wideband phase shifters. This feed architecture generates six distinct polarization modes: horizontal linear polarization, vertical linear polarization, ±45° linear polarization, left-hand circular polarization and right-hand circular polarization, with measured amplitude imbalance below 1 dB and phase ripple within ±6° across the full X-band frequency range of 8–12 GHz.

Fabricated via polymer 3D-printing with a revised physical diameter to accommodate manufacturing constraints, the assembled lens antenna maintains consistent gain values under all polarization configurations, with impedance bandwidth covering 7.8–13.8 GHz and port isolation exceeding 29 dB. Radiation testing in an anechoic far-field chamber verified 360° azimuth beam scanning and ±90° elevation coverage. Relative to equal-size cubic lattice LL counterparts, the diamond lattice prototype achieves reduced sidelobe levels and cuts total mass to 55.8% of conventional designs. The study also establishes a crystallography-driven electromagnetic component optimization workflow that unifies structural, material and wave propagation design parameters, offering a reference framework for lightweight, multi-polarized GRIN lens antennas targeting integrated sensing and communication, satellite payloads and microwave imaging hardware.

The paper “A Diamond-Lattice-Structure-Inspired Full-Polarized Lightweight Steady Isotropic Luneburg Lens,” is authored by Yuechao Wang, Kai Chen, Jun Xu, Ka Fai Chan, Xiaoyue Xia, Sai Ma, Yiqiu Liang, Chi-Hou Chan, Wei Hong. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.12.027. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.