In this letter, a continuously tunable cutoff frequency filter is proposed, which is composed of tunable spoof surface plasmon polaritons (SSPPs) loaded with p-i-n diodes and varactor diodes. The dispersion behavior of the unit structure can be controlled by switching the SSPP unit with a p-i-n diode, accomplishing reconfigurability at two cutoff frequencies of 6.51 and 7.68 GHz. In order to realize more tunable cutoff frequencies, a new unit structure that can obtain a cascaded combination of varactor diodes and p-i-n diodes is presented. The simulated and measured results verify that the cutoff frequency of the filter can be tuned continuously from 5.34 to 7.23 GHz by controlling the magnitude of the biasing voltage, and the relative tunable bandwidth of the SSPP filter is up to 70.8%.

A wideband omnidirectional metasurface antenna has been proposed. The characteristic mode analysis (CMA) was applied to explore the modal behaviors of metasurface and guide the design. The proposed metasurface is designed based on a 5×5 square patched array, which is a hybrid metasurface incorporating square patches with 2×2 and 3×3 sub-arrays in a distributive arrangement, significantly improving the bandwidth and current distribution over a wide band. By properly adjusting the sizes of these elements, the bandwidth and gain are further improved. Based on the predicted excitation of metasurface, a probe center-fed circular patch is introduced on the bottom layer, which not only excites the metasurface but also generates an additional mode to compensate the metasurface for attaining stable omnidirectional radiation. An antenna prototype was simulated, fabricated, and tested. Results show that the proposed antenna achieves a wide bandwidth of 70.1%, a peak gain ranging from 2 to 6 dBi, and radiates a good omnidirectional pattern.

In this letter, a hexa-polarization reconfigurable fixed-frequency beam scanning leaky-wave antenna (LWA) operating in the millimeter-wave band is developed. Two parallel gap waveguides (GWs) are used as the basic transmission structure, and wide serrated ridges are adopted to produce quasi-TEM mode and slow-wave transmission in the GWs. A square patch array excited by the GWs is designed to generate radiation with desired polarization. A control structure loaded with PIN diode is applied to tune the working state of each patch unit. Then based on the holographic theory, the hologram on the antenna aperture can be manipulated by controlling the states of all the patch elements. In this way, six polarizations can be obtained (±45° linear polarizations, horizontal polarization, vertical polarization, left-hand circular polarization and right-hand circular polarization), and independent fixed-frequency beam scanning for each polarization can be achieved. In the measurement, a beam-scanning range of 100° is realized for each polarization state, and the property of two circular polarizations is also verified by the measured axial ratios. Therefore, this LWA shows potential in the millimeter-wave applications that demand polarization agility and fixed-frequency beam scanning.

This letter presents a compact wideband circularly polarized (CP) filtering antenna that integrates split ring resonators (SRRs) and slotted sector-shaped parasitic patches to achieve high-performance filtering, wide bandwidth, and miniaturization without external filtering circuits. The structure of the antenna incorporates two pairs of orthogonal dipoles, four sector parasitic patches with etched slots, two 90° phase delay lines, and four sector SRRs. The SRRs are symmetrically placed, which is able to provide two zeros of radiation out of band and introduce multiple current paths, achieving wide impedance matching and axial ratio bandwidth (ARBW). Two etch slots on the parasitic patch are used to adjust the radiation zeros and out of band suppression level. To ascertain the efficacy of the antenna design, a physical antenna was measured and processed. The measurement results indicate that the antenna has an impedance bandwidth (IBW) of 71.8% (1.32-2.80 GHz), an ARBW of 46.8% (1.67-2.69 GHz). Notably, the antenna attains a peak gain of 7.7 dBic with stable efficiency >90% across the operating band, while maintaining a compact footprint of 0.60λ₀2 (λ₀ at 1.8 GHz). Furthermore, the proposed antenna demonstrates steady gain within the operating frequency band and good sideband selection characteristics.

The propagation and scattering of vortex light beams in complex media have significant implications in the fields of laser imaging, optical manipulation, and communication. This paper investigates the scattering characteristics of vortex light beams from a random rough surface. Firstly, a two-dimensional Gaussian rough surface is generated using the Monte Carlo method combined with the linear filtering method. Subsequently, the vortex beams are decomposed into the superposition of infinite plane waves, and the scattering of each plane wave from the rough surface is calculated using the Kirchhoff Approximation method. Numerical results of the angle distribution and spatial distribution of OAM scattering Laser Radar Cross Section (LRCS) are presented, varying with different surface roughness parameters for a rough aluminum surface and the beam’s parameters. The results demonstrate that the scattering of vortex beams is influenced by the beam’s parameters, such as Orbital Angular Momentum (OAM) mode number and elevation angle, which may bring new insights into vortex wave-matter interactions and their applications in high resolution imaging.

In this letter, a novel double-sided composite spoof surface plasmon polaritons (CSSPPs) unit structure is proposed, which consists of a primary grating unit and an auxiliary grating unit. The CSSPPs structure not only realizes mode conversion without transition structure, but also effectively suppresses high-order mode and optimizes out-of-band suppression. The primary grating structure and auxiliary grating structure of the CSSPPs unit introduce an extra phase difference, which makes the spatial distributions of the electric and magnetic fields of the quasi-TEM waves separate from each other, and converted into TM waves, realizing the mode conversion without transition structure. Furthermore, regulating the phase difference between the auxiliary grating and the primary grating can gradually eliminate high-order mode and optimize out-of-band rejection. In order to better verify the scalability and excellence of the structure, a miniaturized bandpass filter by introducing short-circuited branches is designed. The measured results demonstrate that the filter has an insertion loss of less than 1.06 dB in the passband range of 4.38 - 7.33 GHz and a rejection level of more than 35 dB in the range of 8 - 18 GHz.