Wen-Zhong Lu’s research while affiliated with Huazhong University of Science and Technology and other places

A wideband high-gain metasurface (MTS) antenna array loaded with substrate integrated cavity (SIC) is proposed. Benefiting from the wideband property of MTS-based structures and the high gain property of the SIC structure, a novel wideband high-gain MTS antenna element is designed. By utilizing the slot mode, the TM ₁₀ mode of the MTS, and the TM ₁₂₁ mode of the SIC, the cavity-backed slot-coupled MTS and the high-order mode SIC radiation mechanisms are combined to realize wideband and high-gain radiation. A parametric study is conducted to investigate the design process. The simulated results of the proposed antenna element present an overlaid bandwidth of 40.3% from 7.43 GHz to 11.18 GHz and a maximum gain of 10.40 dBi at 11.00 GHz. On this basis, a planar 4 × 4 array fed by a two-layer feeding network based on substrate integrated waveguide power divider is designed and fabricated. The measured results indicate that the proposed array has an overlaid bandwidth of 34.8% from 7.95 GHz to 11.30 GHz, a measured gain of up to 19.90 dBi, and a maximum aperture efficiency of 80.0%.

A wideband function reconfigurable metamaterial (FRM) with a miniaturized periodic unit and that is capable of switching between cancellation and absorption responses is proposed for radar cross-section (RCS) reduction. The proposed FRM unit is a three-dimensional structure comprising metal ground and two pairwise orthogonally arranged circuit substrates. By regulating the PIN diodes (ON and OFF states), the responses of the proposed FRM unit can switch between two modes. In one mode, wideband absorption is realized for the TE and TM polarized waves. In the other mode, the TE and TM waves are completely reflected with a nearly 180° reflection phase difference. Equivalent circuit models are constructed to provide physical insight into the working mechanism of the switchable structure. Furthermore, a chessboard-like FRM is designed based on the proposed FRM unit to satisfy the phase cancellation principle. The measured results indicate that the proposed FRM can achieve a 10 dB RCS reduction from 2.84 to 7.30 GHz in absorption function and a 10 dB RCS reduction in the range of 2.50-7.44 GHz in cancellation function. The operating frequency bands of these two functions almost overlap. Good agreements between the measured and simulated results are obtained.

A mixed perovskite titanate-aluminate [(1-x)(Sr0.6La0.2Ce0.2Ti0.8Mg0.2O3)-xNdAlO3 for x = 0.1 to 0.4] solid solution was successfully synthesized. X-ray diffraction patterns (XRD) and Rietveld refinement results indicated a stable perovskite phase with a cubic structure, in which Nd³⁺ occupies the A-site randomly while Al³⁺ occupies the B-site. No additional reflection spots (superlattice reflections) were detected in the HRTEM pattern (see SAED), confirming the cubic symmetry. All samples showed small Urbach tails, mainly due to compositional disorder. Microstructural analysis based on atomic force microscopy (AFM) showed no traces of impurity phases. For x = 0.4, excellent microwave dielectric properties (MWD) are obtained with a quality factor (Q × f) of 37,131 GHz at f = 5.2801 GHz, relative permittivity (εr) of 43, and temperature coefficient of resonant frequency (τf) of +1.3 ppm/°C. Variations in εr, Q × f values, and τf may be related to changes in relative density (ρrel), ion polarizability, optical band gap, and tolerance factor, respectively.

1 − x)CaTiO3–xLa(Mg2/3Nb1/3)O3 (CT–LMN; x = 0–1.0) solid solutions were prepared by a solid‐state reaction method. A phase transition from a disordered orthorhombic (Pbnm) structure to a 1:1 ordered monoclinic (P21/n) structure was observed when x increased from 0.5 to 0.6. Some new parameters, such as ionic polarizability in a polyhedron and ionic packing fraction in a polyhedron, were defined to explain the structure–property relationships of CT–LMN ceramics based on the Rietveld refinement results. The measured dielectric constant (εr‐mea) decreased monotonically with B‐site ionic polarizability in the [BO6] octahedron (αDT(B)/V[B]$\alpha _{\rm{D}}^{\rm{T}}( {\rm{B}} )/{V_{[ {\rm{B}} ]}}$) when the x value increased from 0 to 1.0. The quality factor (Qf) was dominated by the packing fraction of B‐site cations in the [BO6] octahedron (PF[B]), and both presented an increasing trend. The temperature coefficient of resonant frequency (τf) decreased from +588.5 to −79.7 ppm/°C, and it was highly correlated to the tolerance factor (t), αDT(B)/αDT(B)V[B]V[B]{{\alpha _D^T( {\rm{B}} )} \mathord{/ {\vphantom {{\alpha _D^T( {\rm{B}} )} {{V_{[ {\rm{B}} ]}}}}} \kern-\nulldelimiterspace} {{V_{[ {\rm{B}} ]}}}} and PF[B]. The highest Qf value is obtained at x = 1.0 when sintered at 1600°C for 10 h with εr = 23.65 ± 0.2, Qf = 33517 ± 2000 GHz (@7.8 GHz), and τf = −79.7 ± 2.0 ppm/°C. Moreover, a near‐zero τf value was achieved at x = 0.4 with εr = 43.52 ± 0.2, Qf = 17239 ± 2000 GHz (@5.2 GHz), and τf = −10.2 ± 2.0 ppm/°C.

Microwave dielectric ceramics with a high-quality factor are vital materials for substrates, dielectric resonators, and filters in millimeter-wave communication systems. Here, a novel microwave dielectric ceramic based on a garnet-type Ca2YZr2Al3O12 compound for bandpass filter was prepared using the solid-state reaction method. Sintering the Ca2YZr2Al3O12 ceramics at 1600 ℃ for 5 h resulted in excellent microwave dielectric properties of εr = 10.81 ± 0.16, Qf = 87628 ± 4000 GHz and τf = -34.3 ± 0.5 ppm/℃. Increasing the Ti⁴⁺ content of the Ca2YZr2-xTixAl3O12 ceramics significantly improved the sintering process. Superior microwave dielectric properties (εr = 11.93 ± 0.15, Qf = 121930 ± 2600 GHz and τf = -30.8 ± 0.4 ppm/℃) were obtained for Ca2YZr2-xTixAl3O12 (x = 0.3) because of its dense microstructure, large grain size and high lattice energy. The Ca2YZr2-xTixAl3O12 (x = 0.3) ceramics were used to fabricate a dual-band bandpass filter with a hairpin structure that exhibited a large return loss (|S11| > 12 dB) and a small insertion loss (|S21| < 0.73 dB). The high performance of the Ca2YZr2-xTixAl3O12 ceramics and the corresponding bandpass filter makes this material a potential candidate for millimeter-wave devices.