Jun Hu

Orbital angular momentum (OAM) waves exhibit orthogonal phase characteristics and have attracted considerable interest in wireless communications, radar imaging, and electromagnetic sensing applications. This paper presents a compact planar OAM filtenna that integrates an incomplete uniform circular array (UCA), a spiral spoof surface plasmon polaritons (SSPPs) waveguide, and a half-mode substrate integrated plasmonic waveguide (HMSIPW) filter. The SSPPs feed excites sequentially rotated circularly polarized elements to generate vortex waves, while the HMSIPW introduces bandpass filtering without increasing the size. Theoretical analysis establishes the mode relation, revealing the OAM generation mechanism. Simulated and measured results confirm frequency-selective radiation from 4.12 to 5.82 GHz, with six modes and mode purities up to 0.96. The proposed filtenna achieves compact, high-purity, and frequency-reconfigurable OAM radiation, showing great potential for wireless communication and radar imaging systems.

This paper presents a hybrid-controlled multifunctional metamaterial (HCMM) that integrates electromagnetic switching and frequency tuning through combined active and microfluidic modulation. The HCMM achieves rapid switching between shielding and transmission states via active control of PIN diodes, while wideband frequency tuning is accomplished by manipulating liquid metals (LMs) in embedded microfluidic channels. Wideband frequency adjustment is demonstrated through discrete coarse-tuning (LM injection/discharge) and continuous fine-tuning (precise LM segments repositioning). The underlying operational mechanisms are analyzed by establishing an equivalent circuit model (ECM). Finally, experimental measurements of a fabricated prototype validate the design, confirming its dual-function reconfigurability in both state switching and frequency adaptation.

In this paper, a multifunctional reconfigurable metamaterial (MRMM), featuring three operating states is introduced based on the multi-scale integration of hierarchical microchannel configuration and liquid metal (LM) regulation strategy. The MRMM can flexibly switch among full-band transmission from 8 to 15 GHz with an insertion loss (IL) of 1 dB, second-order bandpass from 11.64 to 13.72 GHz (also featuring an IL of 1 dB), and full-band shielding from 8 to 15 GHz with a reflection loss (RL) of -15 dB, while exhibiting reliable polarization and angular stability. Subsequently, the physical mechanisms of the MRMM at different states are analyzed using the equivalent circuit method (ECM). Finally, a physical sample of the proposed design is manufactured and tested to validate the effectiveness of simulation results. Both numerical simulations and experimental verifications confirm the wide switchable bandwidth and multistate characteristics of the MRMM.

The EM wave carrying orbital angular momentum (OAM) has a helical phase front and hence called vortex EM wave. This letter presents a theory on the manipulation of vortex waves using metalens with hyperbolic phase compensations. The influence of aperture size on gain and sidelobe levels is studied, and a spectral leakage arising from the truncated Bessel transform is elucidated. Guided by this theory, a cost-effective planar metalens using substrate-integrated waveguides is designed. This metalens consists of two stacked substrates, incorporating 13 by 13 meta-atoms arranged in concentric circular rings. Each meta-atom consists of four layers of double-open square slot patches with varying angles, two substrate-integrated waveguides, and an air gap. The measurement validates the proposed theories. Specifically, the divergence angle of mode -1 is reduced from 43.7° to 9.0° and the gain is increased from 7.55 dBic to 16 dBic. The lens has a bandwidth of 16%.

In this paper, a microwave absorption/transmission switchable frequency selective surface (A/T-SFSS) with enhanced multispectral functionality in the visible and infrared spectra is developed. By simply controlling the flowing liquid medium (pure water in this work), efficient manipulation of two opposite states, absorption and transmission, can be achieved in the microwave frequency band with a wide switchable bandwidth. When functioning as a wideband absorber, the proposed A/T-SFSS exhibits an absorption rate over 90% from 6.50 GHz to 10.48 GHz. Conversely, it can be employed as a transmitter with high selectivity, featuring a second-order passband with two transmission zeros at both sides and an impressive −1 dB transmission bandwidth ranging from 7.04 GHz to 8.47 GHz. The design also demonstrates stable responses under different polarizations and incident angles. Additionally, the proposed A/T-SFSS offers flexibility in tailoring the visible and infrared spectra by actively changing the color and temperature of aqueous solutions. The influences of electromagnetic (EM) parameters and liquid temperature variations on the microwave performance are also thoroughly investigated. Finally, experimental verification through free-space tests of scattering parameters, image analyses of grayscale histogram, and infrared radiation detected by thermal imager provides compelling evidence for the potential of the developed A/T-SFSS. The results demonstrate its remarkable capability to achieve switchable microwave functionality as well as active control of visible light and infrared spectra, which significantly contributes to the field by advancing the development of multifunctional and multispectral structures.

Despite the significant interest in pattern synthesis over the decades, the beam synthesis of orbital angular momentum (OAM) has received relatively little attention. In this paper, we present a time-efficient method for OAM beam synthesis based on multipole moment expansion. The approach introduces the multipole moment term as a transforming level, which separates the excitation coefficients and radiation pattern. We evaluate the performance of our proposed method through several examples and demonstrate its high capability to synthesize multiplex OAM beams with arbitrary-shaped arrays, ensuring reasonable accuracy. The theoretical analysis shows a significant improvement in computational efficiency and a great reduction in computational complexity compared to conventional synthesis methods. Finally, we design, fabricate, and measure a double-ring concentric circular patch antenna array using our proposed method, and the measured results confirm the validity of our approach. The work provides a valuable contribution to the field of OAM beam synthesis and offers a promising avenue for future research.

With characteristics of particular wavefronts and orthogonal modes, the sparse imaging method based on vortex waves could obtain high-resolution reconstruction. However, building a large-scale observation matrix is time-consuming and heavily burdens the whole imaging procedure. Inspired by the spherical harmonic expansion of plane waves, this paper provides a fast super-resolution imaging method based on vortex waves. Featuring spherical harmonic functions and a transformation, an orthogonal matching pursuit algorithm for high-resolution imaging exploits a low-rank matrix decomposition of the observation matrix. Simulation results show that the proposed method exhibits significant efficiency advantages while retaining high resolution, achieving an efficiency of up to 51.4% when applied to a large-scale observation matrix.

This paper presents a compact broadband antenna array with two circular loops featuring different circular-polarized elements rotated sequentially. The inner loop employs truncated square patches, while the outer utilizes truncated pentagon patches. The sequential rotation eliminates the need for phase shifters in the feeding network. The design using truncated square and pentagon elements results in a 12-element demonstration with a radius of only 0.76λ ₀ . X-band simulation and measurement results show simultaneous emission of circularly polarized vortex waves of modes -1 and +2, with an impedance bandwidth of 17% and axial ratio bandwidth of 4.7%.