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.

A wideband high-gain circularly polarized (CP) substrate integrated cavity (SIC) antenna array is presented for millimeter-wave applications. The proposed antenna element is simply composed of a slot-coupled high-order-mode resonant square SIC and a pair of obliquely placed strip-shaped parasitic patches on the top surface of the SIC. The parasitic patches are used to adjust the aperture electromagnetic field distribution and phase of the two orthogonal resonant modes of TM211 and TM121 in the SIC to achieve a high-gain CP radiation, and meanwhile introduce an additional cavity-backed slot-dipole CP radiation to extend axial ratio (AR) bandwidth of the proposed antenna element. By combining the above two high-gain CP radiation mechanisms, a wideband high-gain CP SIC antenna element is achieved. The simulated results of the proposed antenna element show an overlaid bandwidth of 20.36% from 26.20 GHz to 32.14 GHz, while considering the -10-dB reflection coefficient, 3-dB AR, and 3-dB gain bandwidths properties, and a maximum right-hand CP gain of 10.53 dBi at 29.40 GHz. On this basis, a wideband high-gain 8 × 8 CP array fed by a full-corporate substrate integrated waveguide network is designed and fabricated. The measured results show that the proposed array has an overlaid bandwidth of 21.72% from 25.85 GHz to 32.15 GHz and a measured gain of up to 26.10 dBic at 29.00 GHz.

A dual-polarized cross-slot antenna array based on the parallel plate waveguide (PPW) is presented in this paper. A new compact 2×2-element subarray consisting of 4 radiating cross-slots, 4 out cavities, 1 coupling cross-slot, and 1 metallic-block-loaded resonant cavity is firstly proposed to achieve dual-polarization and high efficiency. Two orthogonally arranged H-plane waveguide feed networks combined with the low loss PPW is used to generate a pair of orthogonal plane waves to feed the subarray. To demonstrate the merits of the antenna, an 8×8 array prototype is designed and fabricated. The measured result shows that the aperture efficiency exceeding 60% is obtained throughout the band of 12-12.6 GHz. The isolation between two polarizations is higher than 25 dB over the bandwidth. Therefore, this antenna array can be a good alternative for satellite communications systems in airborne applications.

A 4 × 4 high-gain substrate integrated cavity (SIC) antenna array using multilayered low-temperature co-fired ceramic technology is proposed and designed for W-band applications. The TM211 mode of the SIC is utilized. Two parasitic patches are introduced on the top surface of the SIC to adjust the aperture electromagnetic field distribution of the TM211 mode in the cavity for obtaining a high-gain broadside radiation pattern. A bow tie shape is adopted for the parasitic patches to improve the matching characteristic of the SIC. The SIC is modified to a stepped flared shape to improve the gain characteristic of the antenna element. Subsequently, a two-layer low-loss substrate integrated waveguide feeding network is designed for the 4 × 4 antenna array on the basis of the proposed high-gain SIC radiating element. The proposed antenna array shows a wide measured bandwidth of 17.48% from 81.45 GHz to 97.05 GHz at |S11| < -10 dB and a measured gain of up to 20.3 dBi.

Multispectral stealth technology including terahertz (THz) band will play an increasingly important role in modern military and civil applications. Here, based on the concept of modularization design, two kinds of flexible and transparent metadevices were fabricated for multispectral stealth, covering the visible, infrared (IR), THz, and microwave bands. First, three basic functional blocks for IR, THz, and microwave stealth are designed and fabricated by using flexible and transparent films. And then, via modular assembling, that is, by adding or removing some stealth functional blocks or constituent layers, two multispectral stealth metadevices are readily achieved. Metadevice 1 exhibits THz-microwave dual-band broadband absorption, with average measured absorptivity of 85% in 0.3-1.2 THz and higher than 90% in 9.1-25.1 GHz, suitable for THz-microwave bi-stealth. Metadevice 2 is for IR and microwave bi-stealth, with measured absorptivity higher than 90% in 9.7-27.3 GHz and low emissivity around 0.31 in 8-14 µm. Both metadevices are optically transparent and able to maintain good stealth ability under curved and conformal conditions. Our work offers an alternative approach for designing and fabricating flexible transparent metadevices for multispectral stealth, especially for applications in nonplanar surfaces.