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This paper presents a millimeter-wave (mm-wave) 2-element MIMO antenna with characteristics such as gain, bandwidth, cross-polarization, and mutual coupling controlled by pixelated parasitic patches and a defected ground structure (DGS). Using optometric analysis, the separation between the radiating patch and the initial pixels is fixed, with additional parasitic patches placed at the same distance. The antenna operates over 25.7 to 42 GHz, achieving a 49.39% fractional bandwidth. It has a gain range of 3.2 to 6.35 dBi, peaking at 10.2 dBi. The isolation between elements exceeds 17.2 dB, and cross-polarization improves by 7 dB in both E-plane and H-plane radiations. Measured results closely match simulated results. [ABSTRACT FROM AUTHOR]

Objective: Comparatively assess the fluorescence and color adjustment potentials of paste-type and flowable resin composites performed in cervical restorations. Materials and methods: Five paste-type resin composites and 5 highly-filled flowable composites were investigated (n=5 for each). Class V cavities on 50 extracted A2 shade human central incisors were restored. Cross-polarization (CP) and fluorescence illumination (FI) images were recorded for each restoration. L*a*b* values were analyzed using the Photoshop software and color adjustment (ΔECP) and fluorescence adjustment (ΔEFI) levels were quantitatively assessed. Kruskal Wallis Test, Independent Samples t Test, One Way Anova-Welch test, and Pearson Correlation were used for the statistical analyses. The deemed significance was set at p<.050. Results: Paste-type composites presented significantly lower ΔEFI and ΔECP values than the flowable composites (p=.006 and p<.001 respectively). ΔEFI and ΔECP values were positively correlated (r=0.584; p<.001). Paste-type Gaenial A’chord presented the lowest ΔEFI value [7.67 (5.35 - 10.99)b], while Estelite Asteria presented significantly the highest [19.94 (17.08 - 22.17)c]. Charisma Diamond One Flow presented the highest ΔECP value [3.25 (3.13 - 3.39)a] and Gaenial A’chord presented the lowest [0.79 (0.48 - 0.87)e] which was the only imperceptible score (<0.8). The only clinically acceptable color adjustment was found for Geanial Universal Injectable [1.06 (0.73 - 1.62)e] among the flowable composites. ΔEFI and b* values were positively correlated (r=0.493; p<.001). Conclusions: Color adjustment level and fluorescence adjustment level were considered coherent for particular composite brands. At the same time, both were better for the paste-type composites than the flowable composites on A2 base shade class V restorations. Fluorescence adjustment potential as well as the color adjustment potential varied among different composite brands regarding paste-type and flowable composites. Clinical significance: Understanding both the color and fluorescence adjustment potentials of paste-type and flowable resin-based composite materials is clinically vital to achieve the high-end esthetics. [ABSTRACT FROM AUTHOR]

With the continuous advancement of electromagnetic countermeasures, new types of interference signals (e.g., multi-polarization suppression interference) pose a significant threat to conventional Global Navigation Satellite System (GNSS) services, even when the receiver employs a right-handed circularly polarized (RHCP) anti-jamming array. This paper proposes a receiving signal model for orthogonal circularly polarized (OCP) interference signals based on conventional arrays, following an analysis of the non-ideal characteristics of actual arrays. Furthermore, the mechanism by which OCP interference signals affect anti-jamming performance is examined. Power inversion (PI) and linear constrained minimum variance (LCMV) techniques, applied to both uniform linear arrays and central circular arrays, are utilized to verify the impact of these interference signals. Simulation and physical testing demonstrate that OCP interference significantly affects the interference subspace of the conventional RHCP array, potentially leading to a reduction in the anti-jamming performance of the receiver. To effectively suppress multi-polarization interference, anti-jamming GNSS receivers must either ensure the consistency of cross-polarization among the elements of the array or adopt polarization-sensitive arrays. [ABSTRACT FROM AUTHOR]

Background. Antenna arrays based on dual-polarization elements are used as radiating devices for modern and perspective radio communication systems. The main factor reducing the effectiveness of this approach is the presence of spatial correlation and cross-polarization between elements in the array. These effects can lead to a significant reduction in communication system capacity. Aim. Derive relationships based on the Kronecker model that allow to take into account the polarization properties of antenna elements when calculating the ergodic capacity of a multi-channel communication system. Investigate the influence of the cross-polarization parameter of the antenna element on the capacity. Assess the polarization characteristics of synthesized real antenna elements of various types and their impact on the capacity value. Methods. When deriving the basic relationships, methods of statistical radiophysics and electromagnetic analysis of the propagation channel were used. When synthesizing dual-polarization antenna elements, electrodynamic analysis methods based on Maxwell’s equations were used. Results. Based on the analysis using the derived relationships, it was established that the influence of the cross-polarization properties of the array antenna elements on the capacity of a multi-channel communication system becomes significant when the value of the cross-polarization parameters decreases below 10 dB. It is shown that synthesized real antenna elements of various types have high polarization isolation, which will lead to a slight decrease in the system capacity. Conclusion. The derived relationships and the developed methodology make it possible to estimate the change in the capacity of the communication system when taking into account the cross-polarization properties of the dual-polarization elements of the antenna array. This will allow to optimally select radiating elements for a given system. At the same time, the developed antenna elements of various types satisfy the imposed cross-polarization restrictions.

This study introduces a new approach to achieve flexible impedance matching in a self‐diplexing conventional patch antenna by using paired vias for impedance bandwidth tunability. The antenna design incorporates a rectangular radiating patch, an orthogonal arrangement of a couple of paired vias, and a bottom ground plane. The patch is excited with the help of two orthogonal microstrip feeds aligned along the centerline of the broadside and narrow sides of the patch. The orthogonal vias set enables dynamic impedance matching in two frequency bands, lower and upper ranging from 2 to 3 GHz. Optimized via placement achieves high decoupling between input ports, facilitating the self‐diplexing phenomenon. To validate the proposed concept, a prototype with patch dimensions of 49×40×1.57mm3 $49\times 40\times 1.57\,{\text{mm}}^{3}$ has been analyzed, fabricated, and subjected to comprehensive experimental study. The experimental results demonstrate the successful realization of two distinct operating frequency bands, centered around 2.47 and 2.66 GHz, each exhibiting peak gain values of 5.75 and 6.31 dBi, respectively. The input port isolation values are noteworthy, measuring at −34B and −29.5 dB for lower and upper operating frequency bands, respectively. The design offers a low‐profile, minimally coupled structure with independent band control and the unique ability to simultaneously transmit and receive signals. [ABSTRACT FROM AUTHOR]

Microparticle-assisted nanoscopy (MAN) is a novel emerging technique of direct far-field deeply subwavelength imaging, which has been developed since 2011 as a set of experimental techniques. For a decade, the capability of a simple glass microsphere without fluorescent labels or plasmonic elements to grant a direct, broadband, deeply subwavelength image of a nanostructured object was unexplained. Four years ago, the explanation of MAN via the suppression of diffraction was suggested by the author of the present overview. This explanation was confirmed by extensive full-wave simulations, which agreed with available experimental data and revealed new opportunities for MAN. Although the main goal of the present paper is to review recent works, state-of-the-art concepts in MAN are also reviewed. Moreover, so that the peculiarities of MAN are better outlined, its uniqueness compared to other practically important methods of far-field subwavelength imaging is also discussed. [ABSTRACT FROM AUTHOR]

A choke ring horn antenna has been designed for use as an RF applicator in a compact range in vitro 28 GHz bioelectromagnetic exposure system. The 30 mm × 50 mm horn antenna was fabricated and measured to operate from 27.75 GHz to 34.5 GHz with a −20 dB measured S11 and a measured antenna gain of more than 10 dBi. A wide sectoral (flat top) and symmetric E- and H-plane pattern with a half-power beamwidth of more than 60 degrees was achieved with a cross-polarization discrimination of better than 28 dB. Electromagnetic slots were introduced in the antenna to suppress excess cavity mode radiation which inherently impacts the cross-polarization levels of choke ring antennas. The proposed antenna was successfully integrated into the compact measurement chamber in partnership with the Korea Telecommunication Research Institute (ETRI) and is currently in use for real-time 5G millimeter-wave dosimetry studies. [ABSTRACT FROM AUTHOR]

Copyright of Turkiye Klinikleri Journal of Dental Sciences is the property of Turkiye Klinikleri and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the design of a dual-band terahertz absorber, previously published by Lu et al. (Symmetry 2018, 10, 293), was re-simulated. Our findings showed significantly different absorption results from those published in the article. A detailed analysis was conducted to explain this discrepancy, which was attributed to the reflection of an unaccounted orthogonal component of the waves from the design, rather than absorption. The metasurface design has two resonances at 4.48 THz and 4.76 THz, respectively. It was reported that at these frequencies, the structure achieved absorption of 98.6% and 98.5%, respectively. However, in our results, it was found that at the second resonance (4.76 THz), the structure acted as a strong cross-polarization converter, reflecting a significant amount of incident energy in the cross-polarization component of the reflected wave. When this component is considered in the reflection coefficient calculations, the absorption reduces to 41% (from 98.5%), which is not an acceptable level for an absorber. In addition, the structure was simulated for both lossy and lossless (FR4) substrate cases to understand the effect of substrate losses. The results showed that the absorption response significantly deteriorates at the first resonance (4.48 THz) in the case of a lossy FR4 substrate. [ABSTRACT FROM AUTHOR]

The mutual coupling between the elements of an aperture-fed, dual-polarized, low cross-polarization, scanning phased array microstrip antenna is investigated and a simple rectangular planar resonator between the elements is proposed to reduce the mutual coupling. The mutual coupling effect on antenna performance is studied based on active reflection coefficient. The rectangular resonating structure is positioned on the antenna top layer between patch elements, with dimensions optimized for resonance within the desired frequency range without significantly compromising cross-polarization performance. The antenna is a $2\times 8$ planar-phased array operating in the frequency range of 2.77 - 3.10 GHz using the aperture-coupled dual-polarization elements. Based on simulations and measurements, it is observed that the resonator effectively suppresses mutual coupling between antenna elements by 6 and 7 dB for V- and H-polarizations, respectively while maintaining cross-polarization levels below −35 dB for both polarizations within the required scan angle range. The reduced mutual coupling allows for elements to be placed at a distance of $0.45\lambda $ which in turn supports a scan angle range of −60° to 60° as verified by measurements and simulations. The design is simple enough such that the array size can be increased to achieve very fine beamwidth and high gain needed for polarimetric weather radar applications.

Caral stands as the Americas' oldest city, boasting a heritage spanning 5,000 years. Over time, various natural forces have woven a complex geological stratum. To gain a deeper understanding of the Caral civilization, nonintrusive exploration methodologies like ground penetrating radar (GPR) are beginning to be used. This method safeguards the integrity of ancient subterranean remains. A GPR system is in development, tailored to the [200-500] MHz range, employing a 2×2 antenna array with dual polarization. These features enhance resolution without compromising penetration depth. However, using multiple antennas within complex, multilayered environments introduce impedance band constraints and exacerbates antenna coupling issues. This study assesses the coupling of two antenna candidates: the Vivaldi with defected ground structures (DGS) and the log periodic dipole array (LPDA). The scattering parameters show that the LPDA antenna performed better considering measured and simulated data. Cross-polarization exhibited a broader bandwidth in the LPDA antenna, evident in both simulated and measured data. Additionally, a comprehensive comparison of GPR simulations for each antenna type within an 11-level multilayer medium, with different electromagnetic properties, further highlights LPDA. This antenna boasts a 209 MHz bandwidth and a coupling better than -23 dB for the cross-polarization configuration, firmly showing its best performance. [ABSTRACT FROM AUTHOR]

Summary: This article investigates a compact π‐shaped circularly polarized Minkowski fractal antenna (MFA). The proposed radiator is taking a π‐shape with semicircular cuts along the opposite side of the patch with a V‐cut at the bottom. A second‐order Minkowski fractal curve is implemented on the bottom ground plane. The antenna element is powered by a coaxial probe. The asymmetric structure generates two orthogonal modes, which results in circular polarization. A maximum gain response of 7.1 dBic is observed in the impedance band width (IBW) covering 9.7 to 11.2 GHz. The patch is fabricated on substrate RT/Duroid 5880™ (휀푟=2.2). The antenna has a compact dimension of 0.90λ0 × 0.90λ0 × 0.05λ0 (fr = 10.45 GHz). A good match in the results validates the simulated and measured data in comparison with the existing models from literature with respect to diversity performance, thus making it suitable for radar applications. [ABSTRACT FROM AUTHOR]

In this work, several exact and approximate analytical solutions to the quantum master equation are derived using both classical and non-classical coupling models to describe the kinetics of Hartmann-Hahn cross-polarization (HHCP) and multiple-contact CP (MCCP). Moreover, the analytical solution originally obtained by Naito and McDowell [J. Chem. Phys. 84 (1986) 4181.] is shown to be incorrect and the different regimes of spin diffusion and T1ρ relaxation are characterized by the amplitude of the second stage of the HHCP dynamics and the HHCP/MCCP crossing time. The analysis of the 1H–13C HHCP and MCCP dynamics together with (Lee-Goldburg) 1H T1ρ relaxation experimental data provides a consistent picture of spin dynamics in solid alanine and explains the apparent discrepancies previously observed between T1ρ and T1 relaxation measurements. The CH and CH3 protons relax as expected via spin diffusion towards the NH3 protons but the assumption of common proton spin temperature, in which the bottleneck of relaxation is at the NH3 sites, generally valid for T1 relaxation breaks down for T1ρ relaxation. A diffusion-limited situation in which nuclear Zeeman energy is transferred to the lattice faster than can be supplied by spin diffusion is observed instead.

In this work, a comb‐line leaky‐wave antenna with a pair of wide stubs is proposed with enhanced gain and reduced cross‐polarization. To ensure broadside scanning, three sections of transmission lines are used in the stub with the longitudinal offset. The stubs are placed half‐wavelength apart on both sides of the delay line to achieve high gain and a low‐cross polarization level. The antenna provides 46.8% impedance bandwidth with |S11| below −10 dB. The maximum measured gain and total efficiency are 18.5 dBi and 85%, respectively. The optimized broadside frequency of the leaky‐wave antenna is 10.2 GHz. [ABSTRACT FROM AUTHOR]

Gaofen-3-02 (GF3-02) is the first C-band synthetic aperture radar (SAR) satellite with terrain observation with progressive scans of SAR (TOPSAR) imaging mode in China, which plays an essential role in marine environment monitoring. Given the weak scattering characteristics of the ocean, the system thermal noise superimposed on SAR images has significant interference, especially in cross-polarization channels. Noise-Equivalent Sigma-Zero (NESZ) is a measure of the sensitivity of the radar to areas of low backscatter. The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level. For TOPSAR, NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range. Therefore, the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data. This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm. A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths. According to assessment with wide-swath TOPSAR cross-polarization data, the GF3-02 TOPSAR mode has a very low thermal noise level, which is better than −33 dB at the edge of each beam, and controlled below −38 dB at the center of the beam. The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users. After discussing the relationship between normalized radar cross section (NRCS) and wind speed, we provide a formula for NRCS related to wind speed and radar incidence angle. Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images, the bias is −0.004 8 dB, the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939. [ABSTRACT FROM AUTHOR]

In this article, a low cross‐polarized patch antenna is proposed with simple loading techniques. A metal block is set next to the patch and a coupling fringing field generated by the block compensates for the fringing field distribution asymmetry of the patch, resulting in a lower cross‐polarization. In addition, a shorting pin is loaded to further improve polarization purity. To demonstrate the effectiveness of the proposed scheme, prototypes of the proposed antenna with specific parameters were fabricated and tested. The measured cross‐polarized level can be reduced to below −30 dB, which is greatly lower than that of the traditional patch. [ABSTRACT FROM AUTHOR]

The paper considers the solution of the problem of diffraction of the fundamental wave of a rectangular waveguide H10 on a planar transverse insert based on a chiral metamaterial created on the thin-wire conducting helices. To describe the chiral layer, a particular mathematical model is constructed that takes into account the properties of heterogeneity and dispersion of the permittivity and the chirality parameter of the artificial media. The well-known in physics model of Maxwell Garnett was used to take into account the heterogeneity property. To take into account the permittivity dispersion the Drude–Lorentz formula was applied and for the chirality parameter was used the Condon formula. The problem of diffraction of the rectangular waveguide main wave on a planar layer of a chiral metamaterial was solved by the partial regions method and was reduced to a system of linear algebraic equations for unknown reflection and transmission coefficients. It is shown that in the presence of a transverse chiral layer in the waveguide structure, a wave of the H01 type cross-polarized with respect to the main one arises. An analysis of the frequency dependences of the moduli of the reflection and transmission coefficients of the fundamental H10 and cross-polarized H01 showed that in some narrow frequency intervals in the single-mode gap, situations arise when the fundamental wave type is replaced from H10 to H01 near resonant frequencies. The transmission line under consideration can find application in the creation of frequency selective filters and polarization converters in the microwave range.

This paper proposes a novel method for designing a dual-polarized reconfigurable reflectarray antenna (RRA) based on a symmetrically rotated sub-array operating in a single-band. To improve aperture efficiency and prevent grating lobes, a miniaturized unit cell of a rectangular ring patch with a size of $0.3\lambda _{0}$ is adopted, where the $\lambda _{0}$ is a wavelength in free-space for a center frequency of 10 GHz. By employing the RRA with a symmetrically rotated sub-array, a significant suppression of the cross-polarization level (CPL) and a slight enhancement in peak gain are both achieved. The dual-polarized metasurface with 164 elements is assembled using a feeding structure optimized with F/D = 0.52. The beam steerable RRA is electronically controlled by a control board and has a wide beam steering range of up to ± 60°. The high aperture efficiencies of 26.2% and 27.0%, and relatively low CPLs of −22.6 and −22.8 dB for the $x$ - and $y$ -polarized beams were measured, respectively. Furthermore, the extended functions of the presented RRA, such as dual-polarized dual-beam steering and circular polarized beam steering, are confirmed in full-wave simulation.

In protein nuclear magnetic resonance (NMR), chemical shift assignment provides a wealth of information. However, acquisition of high-quality solid-state NMR spectra depends on protein-specific dynamics. For membrane proteins, bilayer heterogeneity further complicates this observation. Since the efficiency of cross-polarization transfer is strongly entwined with protein dynamics, optimal temperatures for spectral sensitivity and resolution will depend not only on inherent protein dynamics, but temperature-dependent phase properties of the bilayer environment. We acquired 1-, 2-, and 3D homo- and heteronuclear experiments of the chemokine receptor CCR3 in a 7:3 phosphatidylcholine:cholesterol lipid environment. 1D direct polarization, cross polarization (CP), and T2' experiments indicate sample temperatures below − 25 °C facilitate higher CP enhancement and longer-lived transverse relaxation times. T1rho experiments indicate intermediate timescales are minimized below a sample temperature of − 20 °C. 2D DCP NCA experiments indicated optimal CP efficiency and resolution at a sample temperature of − 30 °C, corroborated by linewidth analysis in 3D NCACX at − 30 °C compared to − 5 °C. This optimal temperature is concluded to be directly related the lipid phase transition, measured to be between − 20 and 15 °C based on rINEPT signal of all-trans and trans-gauche lipid acyl conformations. Our results have critical implications in acquisition of SSNMR membrane protein assignment spectra, as we hypothesize that different lipid compositions with different phase transition properties influence protein dynamics and therefore the optimal acquisition temperature. [ABSTRACT FROM AUTHOR]

Interactions between the hierarchical structure of Japanese cypress and small hydroxylic solvents with high polarity were studied using variable-temperature 13C cross-polarization and magic-angle spinning nuclear magnetic resonance (CP/MAS) NMR spectroscopy, including low-temperature measurements. 13C CP/MAS NMR spectra were enhanced by dipolar interactions closely related to 1H–13C magnetization transfer, providing information about the interaction between woody materials and small hydroxyl molecules. The change in interaction was particularly near the melting point of the hydroxylic solvent, where a decrease in the intensity of the cypress carbohydrate signal and the appearance of the signal of solvent molecules were observed. The trend of signal intensity in the variable-temperature 13C CP/MAS NMR spectra of cypress and cellulose fibers in the presence of hydroxylic solvents indicated that the decrease in the carbohydrate signal intensity due to the transfer of magnetization near the melting point of the hydroxyl molecule is greater when the size of the hydroxyl molecule is smaller. Furthermore, molecular association in the nanopores of the hierarchical structure allowed the hydroxyl molecular signals of the impregnated cypress to appear above the melting point. [ABSTRACT FROM AUTHOR]

For 5G sub-6 GHz outdoor applications, a highly isolated two-port rectangular dielectric resonator antenna (RDRA) with UWB MIMO is presented in this research. For isolation enhancement purposes at the lower frequency band (2.27 GHz-2.62 GHz), a longitudinal slot is inserted at the ground plane. For isolation enhancement at the higher frequency band (3.9 GHz-5.73 GHz), an edged hole is inserted in the RDRA. Investigations are conducted on the impacts of slotted ground as well as edged hole radius on isolation. The orthogonal feeding scheme of UWBMIMO RDRA considering both edged hole and slotted ground plane effects are investigated. For the edged hole MIMO RDRA with a slotted ground plane, isolation is better than -24.7 dB at a higher frequency band and is better than -15.5 dB at a lower frequency band. This isolation improvement is explained by the surface current density distribution. The use of an edged hole RDRA and an aperture-coupled orthogonal feeding allows UWB bandwidth and good efficiency performances on the 5G operating bands. To justify the MIMO performance, the envelope correlation coefficient (ECC) and diversity gain (DG) are applied. [ABSTRACT FROM AUTHOR]

When acquiring series of spectra (T1,T2, CP buildup curves, etc.) on samples with poor SNR, we are usually faced with choosing between taking a few points with a large number of scans to maximize the SNR or more points with a smaller number of scans to maximize the information content. In this Letter, we show how low‐rank decomposition can be used to denoise a series of spectra, reducing the trade‐off between the number of scans and the number of experiments. [ABSTRACT FROM AUTHOR]

Dust particles and sand storms can cause attenuation and cross-polarization of electromagnetic wave propagation, especially at high frequencies above 10 GHz. Dust attenuation has been the focus of many research works, mainly with the deployment of a 5G wireless network in the FR-2 band (mmWave band, 23–53 GHz with TDD). This has led to the development of novel models to accurately predict and estimate attenuation. However, the existing review works have not adequately provided extensive taxonomies for these models to show the state-of-art and future research directions. This paper aims to bridge this gap by providing a comprehensive review of all electromagnetic scattering models in terms of their strengths, weaknesses, and applications. Lessons learned from the detailed survey have been stated and discussed extensively. Key findings from this review indicate that all the models developed were limited to the region where they were developed, with frequency and visibility levels as the two main parameters. The survey across regions showed no model was developed for Region 2, including the Americas, Greenland, and some of the eastern Pacific Islands. Among the dry regions of the globe, where dust and sand storms can occur either occasionally or frequently, it can be seen that only a few parts of these desert regions of Africa (Region 1) and Asia (Region 3) have been considered by authors for the development of prediction models for attenuation due to dust storms. Thus, this also shows the limitations of the overall deterministic models and presents the crucial need to develop new models or modify existing models to accurately predict dust attenuation in other regions, particularly in Africa.

Introduction. Due to the increasing number of users, growing rates of data transmission, and rapid advancement of the Internet of Things, the parameter of channel capacity is acquiring greater importance in modern communication systems. In wireless communication systems, capacity limitation occurs due to a low signal-to-noise ratio, one reason for which consists in high losses associated with the propagation of electromagnetic waves. These losses can be compensated using high-gain antenna systems, such as metasurfaces, transmitarrays, or reflectarrays.Aim. Development and research of a one-bit transmit phased antenna array with spatial excitation for use in wireless communication networks across sub-6 GHz frequencies. The issues of reducing the insertion losses associated with the cell geometry and control components are discussed. Account is taken of the parasitic parameters of p–i–ndiodes used as control elements for phase adjustment in a unit cell. Methods for suppressing cross-polarization in a unit cell with the purpose of reducing insertion losses are studied.Materials and methods. The characteristics of unit cells in a transmit antenna array were studied by numerical electrodynamic modeling in the CST Microwave Studio computer-aided design system. The obtained results were confirmed by an experimental study of samples.Results. A unique design of a unit cell comprising the main element of a transmitarray was proposed. On its basis, a transmitarray was designed and manufactured, whose measurements proved the level of insertion losses to be lower than 1.5 dB in the operating frequency band of 210 MHz (3.6 %). The level of cross-polarization was found to be lower than 24 dB, and the gain attenuation did not exceed 2.5 dB in the range of beam deflection from 45° to -45°.Conclusion. The design simplicity, low losses, and acceptable cross-polarization levels of the developed one-bit transmit phased antenna array with spatial excitation confirm its feasibility for modern communication systems.

This study presents an approach for friction velocity and aerodynamic drag coefficient retrieval utilizing C-band VH SAR observations from Sentinel-1. The dataset contained 14 SAR images collected under six hurricane scenes co-analyzed with stepped frequency microwave radiometer (SFMR) measurements. The basis for creating this approach utilizes the results proposed earlier linking the parameters of the atmospheric boundary layer from GPS-dropsondes data to the ocean surface emissivity from SFMR measurements. The obtained dependencies of the ocean surface emissivity on surface friction velocity, aerodynamic drag coefficient, and surface wind speed are analyzed together with the collocated SAR data leading to the new GMF valid for the retrieval of friction velocities ranging from 0.55–1.56 m/s and drag coefficient values ranging from 0.00076–0.00232 for all sub swaths. Within the framework of the proposed approach, dependences of the normalized radar cross-section on the surface wind speed were also obtained and used for comparison with existing GMFs to show that the proposed approach is valid. A good consistency was obtained when comparing our results with H14E and MS1A. As an example the distributions of friction velocity, drag coefficient, and surface wind speed retrieved from the Hurricane Maria SAR image (23 September 2017) were considered. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a two-layer microstrip matched feed for a compact offset reflector with projected diameter equal to 10λ, operating at 3.5 GHz (sub-6 GHz 5G band). The proposed feed consists of a rectangular patch operating in dominant mode at the top layer and a circular patch operating in TM 21 mode below it. Both the microstrip patches are excited using two different ports and the excitation ratio between the two ports is varied to obtain the conjugate field matching required for cross-polar suppression in the reflector pattern. The optimum excitation ratio between the two generated modes are obtained through a parametric study for three different F/D (focal length to diameter) values of 0.4, 0.6 and 0.8. The proposed matched feed is a low cost feed designed on FR4 substrate and its pattern is obtained using HFSS and CST. The reflector pattern of the offset reflector is calculated using geometrical optics technique and verified in HFSS-PO. The cross-polarization in the reflector pattern obtained using both the geometrical optics and HFSS-PO are better than − 40 dB for an offset reflector with F / D = 0.6. The characteristics of the proposed matched feed are verified by comparing the simulation and the measured results of a fabricated prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a simple microstrip patch antenna (MPA) that can reconfigure its polarization states from linear to circular polarization in real-time by means of a PIN diode. An antenna is fed by a 50 O coaxial cable through the substrate of Teflon with relative permittivity of 2.15. The proposed antenna possesses a simple patch with a one-sided corner truncated to achieve polarization reconfigurability. A PIN diode is loaded to connect the main patch with a truncated corner and further maintain dual polarization states such as linear polarization (LP) and circular polarization (CP). Advanced design system (ADS) was used as a simulator to simulate the antenna, and a good understanding was obtained between simulated and measured results. Measured results showed a good agreement with simulated results at all working frequencies of interest. It shows minimum reflection coefficient gain with -10 dB scattering bandwidth 100 MHz for LP states and 170 MHz for CP states. It also shows an axial ratio of 1.56 dB for CP, and the cross-polarization level is also in a satisfying range. [ABSTRACT FROM AUTHOR]

A wideband cross polarization converter with the pixelation approach for X, Ku, and K bands has been presented in this paper. The polarizer consists of copper FR4 combo patched pixels on an FR4 substrate backed by copper. The pixels arrangement on the meta-atom yielded polarization conversion ratio (PCR) >0.9 over a wide frequency range from 10.15 to 27.6 GHz. A broadband FWHM bandwidth of 19.87 GHz is observed for PCR which ranges from 9.26 to 29.13 GHz. The physical mechanism of the linear polarization conversion is analyzed by the spatial profile of the electric and magnetic fields. Further, to validate the simulation results a prototype of the metasurface constating of 17 × 17 meta-atom has been fabricated. A good agreement between the experimental and simulation results has been observed. The designed metasurface when integrated with antennas can be extensively applied for diverse microwave applications for polarization manipulation devices. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Metamaterial-based polarization converters, which have all kinds of polarizations realizable via adjusting metamaterial parameters, have been springing up at an increasing rate. However, the reported metamaterial-based polarization converters suffer from either limited bandwidth or low polarization conversion ratios. In this study, a metamaterial-based polarization converter consisting of multilayer copper split-ring resonators and a copper ground separated by dielectrics was demonstrated and was characterized by the cross-polarization with wideband and high-efficiency. For normal incidence, the simulated results illustrated that the expanded bandwidth benefited from the superposition of cross-polarization electromagnetic resonances around 2.78, 3.09, 3.68, and 4.54 GHz, and the polarization conversion ratio was higher than 99% in the frequency range of 2.73 and 4.63 GHz. For oblique incidence, the design can provide larger angle tolerance in the investigated band, except for a very narrow stopband. Moreover, the experimental results agreed well with the simulations, which verified the reliability of the performance. [ABSTRACT FROM AUTHOR]

A compact, dual‐band metasurface‐based microstrip patch antenna with both linear and circular polarization (CP) for multiband communication is reported in this work. The ingredients in the antenna design consist of a combination of metasurface and metamaterial inspired structures that are demonstrated as an effective technique to correct the beam squint problem and reduce the cross‐polarized radiation, usually experienced by thick substrate‐based broadband CP antennas. A fractal boundary metasurface is introduced to achieve CP over a small frequency band. Eight Electric‐LC resonators are symmetrically placed in the same plane of the radiating patch to widen the CP bandwidth, correct the beam squint, reduce the cross‐polarized radiation, and realize a subwavelength resonance of λ0/5.15 order. The measured impedance bandwidths (|S11| < −10 dB) of the proposed antenna are 7.8% (3.7–4.0 GHz) and 27.58% (5.05–6.65 GHz) in the lower and upper‐frequency band, respectively. The measured 3‐dB axial ratio bandwidth (ARBW) is 24.8% (5070–6510 MHz) at 5.8 GHz. The fabricated prototype has an overall size of 55 × 55 × 4.08 mm (0.696λ0 × 0.696λ0 × 0.051λ0 at 3.8 GHz or 1.063λ0 × 1.063λ0 × 0.078λ0 at 5.8 GHz) with a realized peak gain of 4 dBi in the lower band and 7.1 dBic in the upper band. The measured results are consistent with the simulation results. [ABSTRACT FROM AUTHOR]

We present a 24–30-GHz 256-element dual-polarization transceiver (TRX) phased array based on a 16-element beamformer integrated circuit (BF-IC), 2-element frequency conversion integrated circuit (FC-IC), liquid crystal polymer (LCP)-based combiners and filters, and a tileable package with 64 embedded dual-polarized (dual-pol) antennas. The phased array presented in this work overcomes three key challenges in current 5G millimeter-wave (mmWave) antenna arrays: 1) it supports a dramatic increase in the number of supported fast-access beams; 2) it offers improved power efficiency; and 3) it provides a path to lower solution cost. 1) We enable fast switching among >30000 beams—orders of magnitude improvement over prior work—by employing an on-chip beam calculator in the BF-IC, achieving 200-ns beam setup and 8-ns over-the-air (OTA)-switching time. 2) We enable a module-level transmitter (TX) mode peak power added efficiency (PAE) of 20% using a modular architecture that preserves power amplifier (PA) linearity and efficiency as well as receiver (RX) mode low noise amplifier (LNA) noise figure (NF). The module achieves Psat effective isotropically radiated power (EIRP) of 68.5 dBm and BF-IC NF < 3.9 dB. 3) We lower the solution cost by enabling a wider steering range to reduce the number of phased arrays required in a sectorized coverage scheme, by reducing the IC and package area, and by avoiding calibration. The wider steering range is enabled by using an in-package magnetoelectric dipole antenna (for the first time in silicon-based phased arrays), resulting in steering over ±70° in H- and V-pol in both E- and H-planes without requiring any calibration. Moreover, the module achieves >20-dB cross-polarization isolation across the entire ±70° beam steering range. [ABSTRACT FROM AUTHOR]

An ultrathin and wideband reflective cross-polarization converter is presented in this paper. The design consists of a pair of modified dumbbell shaped resonators which are connected together with a conductive strip. The proposed single-layer THz metasurface achieved a high polarization conversion ratio (PCR) of $\ge$95% in the operating frequency ranging from 1.76–4.26 THz. This wide-bandwidth cross-polarization conversion is obtained by exciting multiple closely spaced resonant frequencies at 1.98 THz, 2.61 THz, 2.95 THz, and 3.93 THz. The working mechanism of the proposed structure is analyzed and the polarizer exhibits an excellent angular stability upto 40$^{0}$ of incidence. Further, the proposed cross-polarizer exhibits continuous tunability of PCR over the operating frequencies when photoconductive silicon (Si) is filled in the gap between pair of dumbbell-resonators. The wideband characteristics and the switchable property show that the proposed reflective cross polarizer is an excellent candidate for manipulation and control of polarization in THz communication systems.

This article presents a novel dual‐polarized tightly coupled tapered slot antenna (TC‐TLA) array. With increased capacitive coupling effects of U‐shaped metallic channels of adjacent flare‐arms of TLA elements, the operational bandwidth for broadside scan increases from 4.4:1 to 5.7:1, and the bandwidth at a 50° scan increases from 3.1:1 to 5.7:1, compared with the conventional TLA array. The proposed TC‐TLA array delivers over 0.35–2 GHz bandwidth, ±50° scanning coverage in the horizontal plane with an active VSWR < 3.5, and <−20 dB cross‐polarization. Prototype for a 4 × 22 dual‐polarized TC‐TLA array fed by 1 to 4 wide‐band power dividers is fabricated and measured. Good agreement is achieved between numerical and measured results. [ABSTRACT FROM AUTHOR]

The solid-state 1H and 13C NMR spectra as well as the 1H-13C cross-polarization upon magic angle spinning (CP MAS) kinetics were studied for poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), i.e. a smart pH- and thermo-responsive polymer. The stereochemical content of PDMAEMA was determined from the complex shaped 13C MAS signal of CH3 group. The kinetic data were processed using the Hirschinger and Raya spin dynamics model that includes the complete scheme of rotating frame spinlattice relaxation pathways. The general solution was adapted for the spin cluster treatment. The earlier studied experimental CP MAS kinetics data of poly [2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), i.e. one of its quaternized form, were revisited and newly processed applying this model. The spin-lattice relaxation of protons in the rotating frame in PDMAEMA and PMETAC occurs in the same scale from one to tens of milliseconds. Very high anisotropy of spin-diffusion was found for both polymers. However, the local disorder of various spin sites in PDMAEMA is significantly higher than in PMETAC. It is characterized by the order parameters 0.71-0.77 and 0.87-0.91, respectively. The main chain in PDMAEMA is also more disordered and more flexible than in PMETAC. [ABSTRACT FROM AUTHOR]

An ultrathin and wideband reflective cross-polarization converter is presented in this paper. The design consists of a pair of modified dumbbell shaped resonators which are connected together with a conductive strip. The proposed single-layer THz metasurface achieved a high polarization conversion ratio (PCR) of $\ge$ 95% in the operating frequency ranging from 1.76–4.26 THz. This wide-bandwidth cross-polarization conversion is obtained by exciting multiple closely spaced resonant frequencies at 1.98 THz, 2.61 THz, 2.95 THz, and 3.93 THz. The working mechanism of the proposed structure is analyzed and the polarizer exhibits an excellent angular stability upto 40 $^{0}$ of incidence. Further, the proposed cross-polarizer exhibits continuous tunability of PCR over the operating frequencies when photoconductive silicon (Si) is filled in the gap between pair of dumbbell-resonators. The wideband characteristics and the switchable property show that the proposed reflective cross polarizer is an excellent candidate for manipulation and control of polarization in THz communication systems. [ABSTRACT FROM AUTHOR]

The paper addresses the design of microstrip fed slot antenna with bandwidth enhancement and minimization of cross-polarization in planar printed configuration. The reference radiating slot antenna resonates at 2.86 GHz having 5.95% – 10 dB bandwidth. Next, the reference slot antenna is loaded with two rectangular loops and four rectangular loops resulting 13.22% and 33.03% −10 dB bandwidth respectively but with poor cross-polarization. To overcome the problem of poor cross-polarization, we have introduced the split ring in one of our antenna design and metallic rings on the bottom of the substrate in another antenna design. These two designs introduce the oppositely directed phi-component of electric field along the radiating slot which cancels out phi-component of electric field, the root cause of increased cross-polarization. [ABSTRACT FROM AUTHOR]

This article represented a heart shape reconfigurable monopole antenna with polarization diversity. The proposed antenna is fed by a 50 O microstrip feed line that is printed on a flexible FR-4 (er=4.4) substrate. The antenna comprises a ring-slot, a cross slot and four positive-intrinsic-negative (PIN) diodes that are soldered on ring slot. Four PIN diodes act as a switch and by controlling these PIN diodes effective current direction is changed hence four various states of polarization are achieved. Four states of polarization such as horizontal linear polarization (H-LP), vertical linear polarization (V-LP), right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) can be switched easily with the help of these PIN diodes and achieved an efficiency of more than 90%. Proposed antenna shows voltage standing wave ratio (VSWR)<2 at all working frequency and -10 dB reflection coefficients (RC) bandwidths (BW) (i.e., S11=-10 dB) about 32.86% for linear polarization (LP) states while RHCP and LHCP states possess BW of about 31.61% and 31.67% respectively. It also shows axial ratio (AR) BW of 3.41% and 2.44% for RHCP and LHCP, respectively. Besides, the antenna has a well-suited omnidirectional pattern with a positive gain of all working frequency of interest where crosspolarization level is much lower than that of antenna gain. [ABSTRACT FROM AUTHOR]

In this paper, a two-port Ultra-Wideband Multiple Inputs Multiple Outputs (UWB MIMO) rectangular Dielectric Resonator Antenna (rDRA) is proposed for 5G sub-6 GHz outdoor applications. An edged hole is inserted at the rDRA edge for isolation enhancement purposes. The effect of edged hole radius on isolation is investigated. Both UWB MIMO rDRA with and without edged holes are investigated for both parallel and orthogonal feed schemes (four scenarios). Isolation better than -22 dB is obtained for orthogonal orientation and edged hole rDRA. Surface current density distribution is used to explain that isolation enhancement. UWB bandwidth and high efficiency are obtained on the operating bands due to the usage of an aperture-coupled feed system and edged hole rDRA. The proposed antenna has two -6 dB operating frequency bands, the lower band (2.25 GHz - 2.52 GHz) and the higher band (3.6 GHz - 5.7 GHz). The Envelope Correlation Coefficient (ECC) and diversity gain DG are used to justify the MIMO antenna performance. Good agreement is obtained between measured and simulated results. [ABSTRACT FROM AUTHOR]