Microwave Frequency Band Research Articles

Integrated Physical Optics for Calculating Electric-Large Metallic Sphere Scattering Irradiated by Vortex Wave in Microwave Frequency Band

In this letter, a novel integrated physical optics (PO) method for calculating high-frequency scattering of nonplane wave is proposed, and the orbital angular momentum (OAM) wave scattering upon an electric-large metallic sphere is illustrated. A high-order Bessel wave expanded by a series of plane wave angular spectra is selected to irradiate a perfect electric conductor sphere. Combining the PO approximation, the scattered field from the facet element is calculated, and the total scattered effect is obtained by vector superposition of the scattering from all facets. The calculated results are verified by the EM simulated software FEKO and scattering measurement experiment. Numerical results show that the scattered field of the vortex wave passing through the standard target still has the OAM characteristics, retaining the same topological charge. It can be seen that the proposed combined PO method is feasible at high frequency and can be extended to solve the scattering of other beams and objects, which has a broad range of applications.

Partition Layout Loading of Frequency Selective Surface Absorbers on the Curved Surfaces for the Significant RCS Reduction

In this article, the significant radar cross section (RCS) reduction of curved surfaces in the low microwave frequency band is reported. The design method of partition layout loading of frequency selective surface (FSS) absorbers to control the surface current is put forward. Comparison of the scattering field intensities of different zones on the curved surface clearly shows that surface current should be suppressed in a large zone to effectively reduce the RCS of the curved surface at these frequencies. FSS absorbers under normal and 45° angle of incidence are designed and placed on the different zones of the curved surface to realize the partition layout loading, and remarkable RCS reduction has been obtained. Specifically, more than 15-dB RCS reduction is achieved in 1.05–1.45 GHz, and absorption above 90% is obtained from 0.95 to 1.5 GHz for TE polarization. The great agreement between the simulated and measured results validates the proposed design method.

Design of novel hexagonal s-band patches antenna array for RFID applications

The design and study of the behavior of antennas adapted to radio-frequency identification RFID tags take on all their importance because they must respond to integration problems and therefore the need to design a structure with minimal dimensions, without however deteriorating their performance. The rise in frequency makes it possible to have short wavelengths so that it becomes possible to have a great integrationas as well as very fast bit rate. But, this induces a smaller range due to the propagation losses according to the model of Friis. In this article, a new patch antenna array for microwave frequency band in radio-frequency identification RFID applications will be presented. The antenna covers the band for the central frequency of 2.45 GHz with better loss characteristics. In addition, the antenna offers a high gain at this frequency. After the digital design of the antenna element, which was carried out using the commercial software CST MWS®, the antenna is printed on an FR4 substrate with a dielectric constant of 4.3 and a thickness of 1.6 mm. The comparison between the simulation results and the measurement results proves that the antenna achieves satisfactory impedance matching and radiation efficiency.

Complementary Multi-Band Dual Polarization Conversion Metasurface and Its RCS Reduction Application

In this paper, we present a metasurface composed of complementary units that can realize orthogonal linear and linear-to-circular polarization conversion in multi-band. Linear polarization conversion has seven high-conversion frequency bands: 9.1–9.7 GHz, 15.6–17.6 GHz, 19.4–19.7 GHz, 21.2–23.1 GHz, 23.5–23.8 GHz, 26.2 GHz, and 27.9 GHz. Linear-to-circular polarization conversion also has seven frequency bands with axial ratios (ARs) less than 3 dB: 8.9–9.0 GHz, 9.9–14.7 GHz, 19.1–19.3 GHz, 23.2–23.35 GHz, 23.4 GHz, 24.1–25.4 GHz, and 27.2–27.8 GHz, with the generation of multiple bands extended by the combination of complementary units. Then, we utilize the combined polarization conversion unit’s mirror placement to form a 4 × 4 array to realize the phase difference cancellation of the reflective field, giving the metasurface the radar cross section (RCS) reduction function and the dual-band 10-dB monostatic RCS reduction bandwidth: 8.9–9.7 GHz and 15.5–26.1 GHz. The measured and simulated results were essentially identical. Because the design uses the complementary units to form an array to expand the polarization conversion frequency bands, it provides a novel idea for future designs and can be applied to multiple microwave frequency bands.

The inhibition of glucose uptake to erythrocytes: microwave dielectric response.

Dielectric spectroscopy has been used in the study and development of non-invasive glucose monitoring (NIGM) sensors, including the range of microwave frequencies. Dielectric relaxation of red blood cell (RBC) cytosolic water in the microwave frequency band has been shown to be sensitive to variations in the glucose concentration of RBC suspensions. It has been hypothesized that this sensitivity stems from the utilization of D-glucose by RBCs. To verify this proposition, RBCs were pretreated with inhibitors of D-glucose uptake (cytochalasin B and forskolin). Then their suspensions were exposed to different D-glucose concentrations as measured by microwave dielectric spectroscopy (MDS) in the 500MHz-40GHz frequency band. After incubation of RBCs with either inhibitor, the dielectric response of water in the cytoplasm, and specifically its relaxation time, demonstrated minimal sensitivity to the change of D-glucose concentration in the medium. This result allows us to conclude that the sensitivity of MDS to glucose uptake is associated with variations in the balance of bulk and bound RBC cytosolic water due to intracellular D-glucose metabolism, verifying the correctness of the initial hypothesis. These findings represent a further argument to establish the dielectric response of water as a marker of glucose variation in RBCs.

Research on Silicon‐Based Terahertz Communication Integrated Circuits

With the increasing number of users and emerging new applications, the demand for mobile data traffic is growing rapidly. The limited spectrum resources of the traditional microwave and millimeter-wave frequency bands can no longer support the future wireless communication systems with higher system capacity and data throughput. The terahertz (THz) frequency bands have abundant spectrum resources, which can provide sufficient bandwidth to expand channel capacity and increase transmission data rate. In addition, with the rapid development of silicon-based semiconductor technology, its characteristic size keeps decreasing, and the radio frequency performance of active devices is gradually approaching the performance of III-V semiconductor technology. The realization of THz communication systems based on low-cost, high-stability, and easy-to-integrate silicon-based process has become a feasible solution. This review summarizes the reported silicon-based THz communication systems, as well as the key sub-circuit chips in these systems, including the local oscillator, power amplifier, low noise amplifier, on-chip antenna and transceiver chip, etc.

A new principle of pulse detection based on terahertz wave plethysmography

This study presents findings in the terahertz (THz) frequency spectrum for non-contact cardiac sensing applications. Cardiac pulse information is simultaneously extracted using THz waves based on the established principles in electronics and optics. The first fundamental principle is micro-Doppler motion effect. This motion based method, primarily using coherent phase information from the radar receiver, has been widely exploited in microwave frequency bands and has recently found popularity in millimeter waves (mmWave) for breathe rate and heart rate detection. The second fundamental principle is reflectance based optical measurement using infrared or visible light. The variation in the light reflection is proportional to the volumetric change of the heart, often referred as photoplethysmography (PPG). Herein, we introduce the concept of terahertz-wave-plethysmography (TPG), which detects blood volume changes in the upper dermis tissue layer by measuring the reflectance of THz waves, similar to the existing remote PPG (rPPG) principle. The TPG principle is justified by scientific deduction, electromagnetic wave simulations and carefully designed experimental demonstrations. Additionally, pulse measurements from various peripheral body parts of interest (BOI), palm, inner elbow, temple, fingertip and forehead, are demonstrated using a wideband THz sensing system developed by the Terahertz Electronics Lab at Arizona State University, Tempe. Among the BOIs under test, it is found that the measurements from forehead BOI gives the best accuracy with mean heart rate (HR) estimation error 1.51 beats per minute (BPM) and standard deviation 1.08 BPM. The results validate the feasibility of TPG for direct pulse monitoring. A comparative study on pulse sensitivity is conducted between TPG and rPPG. The results indicate that the TPG contains more pulsatile information from the forehead BOI than that in the rPPG signals in regular office lighting condition and thus generate better heart rate estimation statistic in the form of empirical cumulative distribution function of HR estimation error. Last but not least, TPG penetrability test for covered skin is demonstrated using two types of garment materials commonly used in daily life.

Polarimetric Radar Quantitative Precipitation Estimation

Radar quantitative precipitation estimation (QPE) is one of the primary tasks of weather radars. The QPE quality was substantially improved after polarimetric upgrade of the radars. This study provides an overview of existing polarimetric methodologies for rain and snow estimation and their operational implementation. The variability of drop size distributions (DSDs) is a primary factor affecting the quality of rainfall estimation and its impact on the performance of various radar rainfall relations at S, C, and X microwave frequency bands is one of the focuses of this review. The radar rainfall estimation algorithms based on the use of specific attenuation A and specific differential phase KDP are the most efficient. Their brief description is presented and possible ways for their further optimization are discussed. Polarimetric techniques for the vertical profile of reflectivity (VPR) correction at longer distances from the radar are also summarized. Radar quantification of snow is particularly challenging and it is demonstrated that polarimetric methods for snow measurements show good promise. Finally, the article presents a summary of the latest operational radar QPE products available in the US by integration of the information from the WSR-88D radars via the Multi-Radar Multi-Sensor (MRMS) platform.

Role of cashew shell biochar on EMI shielding behaviour of carbon fibre–epoxy nanocomposites in E, F, I and J band–microwave frequencies

Role of cashew shell biochar on EMI shielding behaviour of carbon fibre–epoxy nanocomposites in E, F, I and J band–microwave frequencies

Combining Pancharatnam–Berry Phase and Conformal Coding Metasurface for Dual-Band RCS Reduction

A flexible, dual-broadband, and polarization-insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1 bit coding units “0” and “1” are formed by the Pancharatnam–Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this communication can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26–12.87 and 14.84–19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained, while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects.

Bimetallic nanoarrays embedded in three-dimensional carbon foam as lightweight and efficient microwave absorbers

The rapid development of electronic information technology has promoted the use of a large number of high-frequency electronic equipment, which has led to increasingly serious electromagnetic interference (EMI) problems caused by disordered radiation. At present, for the 2–18 GHz microwave frequency band, it is still a huge challenge to develop high-efficiency absorbing materials with ultra-wide absorption band (>7 GHz) under thin thickness (<3 mm). Here, we propose a new strategy to achieve lightweight and high-efficiency microwave absorption by constructing hierarchical special structures. The melamine foam template was coated with a carbon/nickel/cobalt organic precursor by a hydrothermal process using a water/ethanol mixed solvent, and then annealed in an inert atmosphere at a high temperature to obtain a bimetallic nanoarray composed of nickel/cobalt embedded three-dimensional carbon foam (BNA/3dCF). This new type of absorbing material completely retains the structure of the melamine foam template, greatly enhances the conduction ability of micro-currents, and provides a large number of scattering sites for electromagnetic wave conduction. Interestingly, the protection of the carbon layer effectively avoids the oxidation of the bimetallic nanoarray, so that the BNA/3dCF retains the good dielectric properties of the carbon foam and has excellent magnetic properties, and improves the impedance matching and magnetic loss capabilities. With matching thicknesses of 2.2 mm and 3.9 mm, BNA/3dCF can respectively obtain an ultra-wideband microwave absorption of 7.16 GHz and a minimum reflection loss of −57.84 dB. We believe that through the macro/meso/micro multi-scale precise control of the absorbing material, it is an effective solution to enhance its absorbing performance.

Coherent Spatially Varying Bidirectional Scattering Distribution Function of Rough Surface

High-resolution synthetic aperture radar (SAR) as an imaging device becomes more and more like a “camera” at the microwave frequency band. How different objects or object surfaces may visually appear in SAR images becomes an interesting research topic. Inspired by the bidirectional reflectance distribution function (BRDF) models employed in computer graphics (CGs), this article proposes the coherent spatially varying bidirectional scattering distribution function (CSVBSDF) for characterizing the electromagnetic scattering and SAR imaging behavior of surfaces. The CSVBSDF establishes a mapping function from observation parameters and surface local parameters to multidimensional measurements. In this article, CSVBSDF of the randomly rough surface is derived via adapting the integral equation method (IEM) to finite-size pixel cells under the plane wave and tapered wave incidence, respectively. It is then validated against the numerical beam simulation method (BSM) in the SAR image domain. A ground-based rail SAR and a 3-D laser scanner are used to measure the SAR image and the corresponding 3-D geometry of a real ground surface. Surface-local parameters, such as the local slope and roughness, are estimated from the measured 3-D geometry and then fed into the CSVBSDF model to produce a synthetic SAR image. Comparison against the real SAR image preliminarily demonstrates the efficacy of the proposed CSVBSDF model.

Lift-Off and Tilt Effect in Microwave Surface Resistance Measurement Using TE011 Mode Cylindrical Cavity

Measurement of surface resistance at microwave or higher frequency bands is needed for applications, such as accelerators, microwave systems, and integrated circuits. Cylindrical cavity resonators operating at TE₀₁₁ mode have been applied in surface resistance measurement for decades. It is common that samples under test are usually used as one of the cavity&#x2019;s endplates and contact the cylinder side wall directly, which cannot be regarded as noncontact measurement. In this article, through quantitative research on lift-off effect of samples under test, we explore the possibility of realizing noncontact surface resistance measurement by intentionally introducing an air gap (ranging from &#x007E;0 to 10 mm) between the samples and the cavity side wall. From the results of both electromagnetic simulations and experiments, it can be concluded that by taking care of the sample&#x2019;s tilt effect, surface resistance can be measured in a noncontact manner. Measurement results of polished metal plates with electrical conductivity ranging from &#x007E;2 to 58 MS/m (measured with standard eddy current method) show that the relative measurement error is expected to be less than 10&#x0025;. Compared with related publications, the focus of this work is put on the lift-off effect and a larger range of air gap is introduced. The obtained results indicate that the air-gap size may be an additional consideration in the design of surface resistance measurement system for special applications, such as temperature-dependent measurements in vacuum chamber, <i>in situ</i> diagnosis tools.

Design and Analysis of Novel Antenna for Millimeter-Wave Communication

At present, the microwave frequency band bandwidth used for mobile communication is only 600 MHz. In 2020, the 5G mobile Communication required about 1 GHz of bandwidth, so people need to tap new spectrum resources to meet the development needs of mobile Internet traffic that will increase by 1,000 times in the next 10 years. Utilize the potentially large bandwidth (30∼300 GHz) of the millimeter wave frequency band to provide higher data rates is regarded as the potential development trend of the future wireless communication technology. A microstrip patch implementation approach based on electromagnetic coupling feeding is presented to increase the bandwidth of a dual-polarized millimeter-wave antenna. To extend the antenna unit's impedance bandwidth, coplanar parasitic patches and spatial parallel parasitic patches are used, and a 22 sub-array antenna is developed using paired inverse feed technology. The standing wave at the centre frequency of 37.5 GHz is less than 2 GHz. The antenna array's relative bandwidth is 6.13 percent, the isolation is >30 dB, the cross-polarization is −23.6 dB, and the gain is 11.5 dBi, according to the norm. The proposed dual-polarized microstrip antenna has the characteristics of wide frequency bandwidth, large port isolation, low cross-polarization, and high gain. The antenna performance meets the general engineering requirements of millimeter-wave dual-polarized antennas.

Comparison of Materials Characterization Methods Using One-Port and Two-Port Transmission Line Principles

Over the years, the demands on dielectric and magnetic materials are steadily increasing. At the same time, since microwave frequency bands are used, measurements intrinsic parameter technique is increased to miniaturize components, devices, and developed technologies. Among the methods used, the lines technique in transmission and reflection, based on the use of distributed elements, which is a broadband method, is presented in this paper through a study comparison in terms of the covered frequency range, the technique implementation simplicity, the extracted parameter elements, and their accuracy. Due to the limits of each structure implementation, the scanned frequency [1 – 20] GHz is investigated with Laurentiis, Semolina, Polenta, Aquarium Sand, and ceramic powder (Q-Cell 5020). Two identical circular coaxial cells are utilized as specimen holders, fabricated with the brass conductor, with different lengths. Two main principles are presented (one-port and two-port techniques) through three configurations, namely: line in transmission, short-terminated and open-ended positions. The study comparison has brought out that the choice of the method to be used depends on the condition of the material (shape, insertion, number of extracted parameters, expected accuracy, etc.) and the frequency range of validation along with their scope of use.

Shared-Aperture 24–28 GHz Waveguide Antenna Array

A compact three-element shared-aperture waveguide antenna array for the 24–28 GHz microwave-frequency band is presented as a proof-of-concept of an array with steerable directional beam suitable for 5G telecommunication systems. The array is intended for use in a microwave photonic link and is sufficiently steerable only with the progressively phased excitation signals of equal magnitudes. The mutual interactions between the array elements are minimized to maintain the properties of the individual elements, even if they are embedded and closely spaced in the array. The proposed concept could be simply extended by adding more elements to further increase the directivity and enhance the steering properties of the array.

Photonic Crystal 180° Ring-Shaped Hybrid: From Microwave to Optics

In this letter, a 180° ring-shaped hybrid based on the photonic crystal structure (PCS) is presented. The ring hybrid is designed for the operation wavelength of 1550 nm. Initially, a 180° hybrid is a design based on conventional microwave procedures. Different wave behavior inside the structure in THz and microwave frequency band has caused the wave propagation in this structure to change especially in terms of phase. By analyzing the field distribution within a structure, the rod arrangement is modified. In proposed structure, the phase difference between the output ports is greatly improved (about 90°). Also, by reducing the leakage and improving the matching, the output power of the ports tends to half power. Moreover, 32 nm wavelength shift is improved. The proposed structure's reflectance value is less than 20 dB at the desired wavelength. The power splitting ratio between the two output ports is improved up to -3.7 dB and the power of the isolated port is less than -20 dB. This work has been analyzed using the FDTD method.

An Ultrawideband Microfabricated Gold-Based Antenna Array for Terahertz Communication

The microwave frequency band typically used for wireless communications will soon become saturated and will no longer be able to fulfill the high bandwidth demands of modern communication networks. Terahertz (THz) communication has appeared as a highly attractive, future-generation wireless technology that offers higher spectral bandwidth and, therefore, higher data rates. However, the full exploitation of THz technologies is contingent upon the availability of energy-efficient sources and devices. In this letter, we present a fabrication and measurement of a microscale planar inverted cone antenna array made of gold. Using an ungrounded coplanar waveguide (CPW) feed, the microfabricated structure provides a bandwidth of 37.9% with the resonant frequency of 0.925 THz. Given the cost of microfabrication is reduced substantially with rapid technological advancements, the results of this letter suggest that high-speed THz communications can be realized for wide-scale applications.

Defective Microwave Photonic Crystals for Salinity Detection

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium is developed to calculate the transmittance spectra of the sensors. It is found that the peak transmittance of both the defective resonance within the microwave band gap (MBG) and transmitting modes outside the MBG monotonously decrease with the increase of salinity, while the resonant and transmitting mode frequencies remain unchanged. By comparing the four MPC sensor structures, the first transmitting mode in the upper frequency band outside the MBG of the 15-layer MPC sensor has the largest salinity sensing range from 0 to 40‰ with relative stable detecting sensitivity. The sensing principle is based on the fact that the dielectric loss factor of saline solution is much more sensitive to salinity than the dielectric constant in the microwave frequency band. The sensitivity, quality factor, and salinity detection range of the MPC sensors are calculated and compared. The reported defective MPC sensors are suitable to be used for non-contact salinity detection.

Fat tissue equivalent phantoms for microwave applications by reinforcing gelatin with nanocellulose

Tissue mimicking phantom materials with thermal and dielectric equivalence are vital for the development of microwave diagnostics and treatment. The current phantoms representing fat tissue are challenged by mechanical integrity at relevant temperatures coupled with complex production protocols. We have employed two types of nanocellulose (cellulose nanocrystals and oxidized cellulose nanocrystals) as reinforcement in gelatin stabilized emulsions for mimicking fat tissue. The nanocellulose-gelatin stabilized emulsions were evaluated for their dielectric properties, the moduli-temperature dependence using small deformation rheology, stress-strain behavior using large deformation, and their compliance to quality assurance guidelines for superficial hyperthermia. All emulsions had low permittivity and conductivity within the lower microwave frequency band, accompanied by fat equivalent thermal properties. Small deformation rheology showed reduced temperature dependence of the moduli upon addition of nanocellulose, independent of type. The cellulose nanocrystals gelatin reinforced emulsion complied with the quality assurance guidelines. Hence, we demonstrate that the addition of cellulose nanocrystals to gelatin stabilized emulsions has the potential to be used as fat phantoms for the development of microwave diagnostics and treatment.