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In order to improve the sensitivity of liquid dielectric constant measurements, a liquid dielectric constant sensor based on a cubic container structure is proposed for the first time. The cubic container, which consists of a dielectric substrate with a split resonant ring (SRR) and microstrip lines, can enhance the electric field intensity in the measuring area. High sensitivity can be obtained from measuring the dielectric constant with the characteristics of the structure resonate. The research results show that the resonant frequency of the sensor is shifted from 7.69 GHz to 5.70 GHz, with about a 2 GHz frequency offset, when the dielectric constant of the sample varied from 1 to 10. A resonance frequency offset of 200 MHz for the per unit dielectric constant is achieved, which is excellent regarding performance. The permittivity of oil with a different metal content is measured by using the relation between the fitted permittivity and the resonant frequency. The relative error is less than 1.5% and the sensitivity of measuring is up to 3.45%.

In order to solve the low-sensitivity problem of the dielectric constant with the resonant cavity method, a sensor based on a substrate-integrated waveguide structure loaded with a multi-complementary open resonant ring is proposed. With the enhanced resonance characteristics of the sensor, this design realized the measurement of complex dielectric constants in a wide range. The frequency selectivity of the sensor is improved by the high-quality factor of the substrate-integrated waveguide. By loading three complementary resonant rings with different opening directions in the ground plane, a deeper notch and better out-of-band suppression are achieved. The effect of the complex dielectric constant on both resonant frequency and quality factor is discussed by calculating the material under test with a known dielectric constant. Simulation and experimental results show that a resonance frequency offset of 102 MHz for the per unit dielectric constant is achieved. A wide frequency offset is the prerequisite for accurate measurement. The measurement results of four plates match well with the standard values, with a relative error of the real part of the dielectric constant of less than 2% and an error of less than 0.0099 for the imaginary part.

In this paper, a spatial-multiplexing-based transmission-reflection-integrated full-space metasurface (FS-MS) is proposed, which is applied to the generation of orbital angular momentum (OAM) beam. Using the principles of anisotropy and spatial multiplexing, the metasurface element is designed. The element consists of three dielectric substrates and four metal layers, which are of conventional cross-shaped and slotted cross-shaped construction. The designed element has the ability to independently modulate transmitted and reflected electromagnetic (EM) waves at 15 GHz. When EM waves with different polarizations are incident, the metasurface is capable of transmission at the incident x-polarized waves and reflection at the incident y-polarized waves. Using the designed element, the FSMS was designed by combining the theories of OAM beam generation and phase superposition. The results show that the metasurface can generate the OAM beam with the topological charge of +2 in the transmission mode and +3 in the reflection mode at 15 GHz. The purity of the generated OAM beam is 78.88% in transmission mode and 72.87% in reflection mode. The metasurface proposed in this paper is characterized by the integration of transmission and reflection, which is valuable for applications in wireless communications, sensing, and imaging. [ABSTRACT FROM AUTHOR]

In this paper, a transmissive linear-to-circular polarization conversion (LCPC) multibeam metasurface is presented which shows promise for point-to-multipoint transmission in satellite communications under interference conditions. The unit cell consists of four identical metal layers and three dielectric substrates, where each metal layer includes a square ring and a cross-shaped structure. By altering the arm length of the cross-shaped structure, independent control of the phase of x- and y-polarized waves can be achieved. Thus, by keeping the amplitude of the x- and y-polarized waves equal and the phase difference at 90◦ , LCPC is realized. Based on the multibeam superposition theorem, the metasurface array is arranged using four discrete elements with a phase gradient of 90◦ . It can convert linearly polarized (LP) waves into right-handed circularly polarized (RHCP) waves and generate transmitted multibeam at predetermined angles and gain ratios. Three-beam LCPC metasurfaces with equal and unequal gain in the Ka-band (26 to 40 GHz) were demonstrated to validate the proposed unit cell and methods. The equal gain metasurface has an approximate 6% bandwidth for the 3 dB axial ratio (AR) and a 6% bandwidth for the 1 dB realized gain. Furthermore, at the center frequency of 30 GHz, the unequal gain metasurface achieves gains of 22.9 dBi, 19.7 dBi, and 17.3 dBi, respectively, with an AR of less than 2 dB for all three beams. [ABSTRACT FROM AUTHOR]

To enhance the reduction of radar cross section (RCS) and improve stealth performance, a phase cancellation and absorbing metasurface (PCAM) is designed in this paper. The PCAM is composed of a chessboard layout of circular units and square units, and it not only converts absorbed incident electromagnetic waves into heat to reduce the intensity of reflected electromagnetic waves but also simultaneously controls the phase of the reflected electromagnetic waves, achieving phase cancellation. This enables the metasurface to be exhibited with ultralow backscatter. After simulation verification, the metasurface can achieve RCS reduction of over 15 dB in the 4.3-11 GHz range for vertical incidence, with a fractional bandwidth of approximately 87.6% and over 15 dB in the 5.4-11.2 GHz range for a 30° oblique incidence, demonstrating good stability for oblique angles. The metasurface has increased the reduction level from over 10 dB to over 15 dB, significantly enhancing the RCS reduction. Additionally, in the co-planar state with a central curvature of 90°, it can also achieve RCS reduction of over 10 dB in the 3.2-9.9 GHz range, showing significant potential for practical applications. [ABSTRACT FROM AUTHOR]

The multifunctional metasurface offers a high degree of flexibility in manipulating electromagnetic waves. However, the majority of its functions are limited to the reflection or transmission space in a single band, restricting the utilization of electromagnetic information. This paper proposes a three-channel multifunctional frequency multiplexing coding metasurface based on the Fabry-Perot cavity principle. It consists of two layers of orthogonal metal gratings and a cross-shaped, oblique open loop structure in the intermediate layer. Simulation results reveal that at an incidence of 22 GHz, the polarization conversion and focusing functions of the transmitted wave are accomplished. Similarly, at an incidence of 31 GHz, the beam deflection function of the reflected wave is observed. Furthermore, at an incidence of 32 GHz, the radar scattering cross-section reduction function of the reflected wave is achieved. In addition to achieving high efficiency, miniaturization, and compactness, the proposed metasurface effectively enhances the spatial utilization of electromagnetic information. As a result, potential applications in multifunctional integrated systems, including wireless communication, sensing technologies, and radar systems, are vast. [ABSTRACT FROM AUTHOR]

Orbital angular moment modes (OAMs) have been proven to be promising resources for increasing communication capacity. To generate wideband and high purity OAM, we have proposed a transmitting metasurface with amplitude-phase dual control. The proposed unit cell is a novel split ring structure with upper and lower grating-like structures. By changing the direction angle and rotation angle of the split-ring unit, the cross-polarization phase response and amplitude response of the unit are controlled respectively. The amplitude distribution of the metasurface array is calculated using Chebyshev synthesis method (CSM). We designed metasurface arrays with mode numbers l = 1, 2, 3, and it generated high purity OAM beams in the frequency band of 22-32 GHz. Compared with traditional phase-control metasurface, amplitude-phase control surface can effectively improve the quality of OAM generation. The results have verified the accuracy of the proposed method, and the proposed method has potential applications in future communication system. [ABSTRACT FROM AUTHOR]

Aiming at the focusing of near-field electromagnetic (EM) energy, a design approach of multi-type focusing (MTF) based on 1-bit metasurface is proposed in this paper. The surface electric field required for multi-focus is actually obtained by the superposition of the surface electric field of each single focus. This method can flexibly design the number, position, and energy distribution ratio of the focus according to the phase arrangement of the metasurface. Dipole structure is used as “0” and “1” unit of 1-bit metasurface. The phase difference of reflection is 180◦, and the reflection coefficient is over 90% in 7.4–21.9 GHz. Using this 1-bit unit, the linear focus metasurface, multi-focus metasurface, and metasurface generating two foci with different energy distribution are realized respectively. The energy distribution metasurface was manufactured and measured, and the measured results are consistent with the simulations. The design method used in this paper is simple and effective to realize multifocus metasurface design and has potential application value in microwave imaging, radio frequency identification (RFID), and wireless power transmission. [ABSTRACT FROM AUTHOR]

In general, a single beam reflection can be realized by 2-bit coding metasurfaces. In order to obtain multi-beam reflection, a design method for coding sequence based on 2-bit coding metasurfaces is proposed, which can manipulate the direction of reflected beams by 2-bit addition rule and control the number of reflected beams by addition theorem on complex codes. This method simplifies the design process of coding sequence, and the direction and number of multi-beams can be flexibly designed. In this paper, the design of dual-beam reflection is taken as an example to illustrate the design process of coding sequence. Both simulation and measurement results show that the designed metasurface realizes the dual-beam reflection, and the direction of reflected beams is consistent with expectations. The proposed method is of great significance for the design of multi-beam reflection based on coding metasurfaces. [ABSTRACT FROM AUTHOR]

Radar cross section (RCS) reduction technology has great significance in stealth and other fields. A PSO-FSP algorithm is proposed based on the particle swarm optimization algorithm and the far-field scattering characteristics of coding metasurface to obtain the optimized coding sequence for RCS reduction. According to the principle of coding metamaterial, a 1 bit cell structure is designed. Therefore, a coding metasurface is constructed by arranging the unit cells based on the optimized coding sequence. Simulation results show that, in the case of vertical incidence, compared with metal plates of the same size, the metasurface can achieve more than 10 dB of RCS reduction within the broadband range from 15GHz to 35GHz, and the maximum reduction can reach 36 dB. The proposed coding metasurface has been successfully fabricated and measured, and there is a good agreement between simulated and measured results. [ABSTRACT FROM AUTHOR]

A novel miniaturized bandpass half-mode substrate integrated waveguide (HMSIW) filter which uses dual-iris coupling method to load complementary split-ring resonators (CSRRs) into HMSIW is proposed in this paper. By modifying traditional CSRRs through nesting method combined with step impedance structure, a nested stepped-impedance complementary split-ring resonator (NSICSRR) structure with higher equivalent capacitance and inductance of CSRR is obtained. Based on the traditional single-iris coupling method, a dual-iris coupling method is developed. And NSICSRR is loaded into HMSIW by using the dual-iris coupling method, which can reduce the resonant frequency of the structure. In order to verify the effectiveness of the technology above in realizing the miniaturization of HMSIW filter, a second-order HMSIW filter is designed and measured. It can be found in the measured results that the filter has the center frequency of 6.35GHz, the 3 dB bandwidth of 690MHz, the return loss of better than 14 dB within the passband, and the size of 0.0396λg². The experimental results are basically consistent with the simulation ones. [ABSTRACT FROM AUTHOR]

A novel dual-wideband dual-polarised magnetoelectric (ME) dipole antenna for the fourth generation (4G)/fifth generation (5G) microcell base station is proposed. Using a pair of orthogonal ME dipoles and Γ-shaped tapered cross feeding lines, the initial antenna achieves dual-band and dual-polarised. Then, four U-shaped gaps, added in electric dipoles, effectively extend the lower impedance bandwidth. Finally, a circular parasitic patch with capacitive properties is innovatively loaded above the ME antenna, which obviously reduces the high-resonant frequency from 5.5 to 4.9 GHz. Meanwhile, a box-shaped reflector is employed to achieve stable gain and radiation patterns. As a result, the measured results show the good dual-wideband performance of 52.4% (2.14--3.66 GHz) and 7.4% (4.68--5.04 GHz) with voltage standing wave ratio (VSWR) < 2, high isolation (>25 dB) and high gain (9.5 and 5.5 dBi, respectively). In addition, a stable radiation pattern with a half-power beam width of 63.5°+6.8° and good cross-polarisation discrimination (>20 dB) on the E-plane is realised over these two bands. [ABSTRACT FROM AUTHOR]