A flexible and reliable full-wave modal integral method is proposed to efficiently characterize planar transmission structures printed on multilayered isotropic/anisotropic substrates. Based on the mathematical concept of operators used in electromagnetism, it consists in determining the modal inner products obtained through the Galerkin's procedure via a proper choice of trial functions with metallic edge effects. To this aim, a fast and accurate nonuniform discretization algorithm is introduced for the first time, while using a new process to accelerate the convergence with regard to the number of areas of such inner products, thus significantly reducing the required CPU-time for planar transmission lines analysis. To demonstrate the efficiency of the proposed numerical integral approach, a successful comparison was achieved through a close agreement with published data.

Aiming at the shortcomings of complex broadband transmitter/receiver systems and inflexible bandwidth control in the existing inverse synthetic aperture radar (ISAR) imaging systems, in this paper, a novel two-dimensional imaging method based on frequency diverse ISAR (FDISAR) is proposed by combining frequency diversity technique with inverse synthetic aperture technique. In the imaging process, FDISAR is different from the stepped-frequency ISAR, which needs to transmit the same burst at different observation moments. Once the bandwidth is determined, the bandwidth of the subsequent burst synthesis cannot be changed, which reduces the flexibility of the radar system. In this method, single-frequency signals of different frequencies are transmitted to the target at different observation times, and the wideband signals are synthesized using the frequencies at different observation times to obtain the resolution capability in the range direction. In addition, the relative motion synthetic aperture of the target and radar is used to obtain the azimuth resolution capability, and finally the two-dimensional imaging capability of the moving target is formed. Specifically, we established an ISAR imaging model based on frequency diversity to synthesize a broadband signal, and used an improved backward projection algorithm (BP) to complete the two-dimensional imaging of the target. On this basis, the influence of the transmission signal frequency selection on the imaging quality is analyzed, and the half-power resolution in range and azimuth directions is derived. Furthermore, in order to eliminate side lobes and improve imaging quality, we combined compressive sensing (CS) theory with a BP imaging algorithm based on compressed sensing to obtain high-quality target 2D images. Simulation and actual measurement results show that FDISAR can achieve two-dimensional imaging of moving multi-scattering point targets. The application of this method is of great significance for reducing the complexity of the ISAR imaging system and improving the flexibility of the system's control bandwidth resources.

In this communication, a compact Dielectric Resonator (DR) based multiple-input-multiple-output (MIMO) antenna is presented for wideband applications. The antenna consists of two modified kite-shaped monopoles where four DRs have been placed on the patch. Corners of four DRs have been etched to implement the orthogonal phase, which leads to circular polarization characteristics. Implementation of DRs also helps in bandwidth enhancement purpose. Two L-shaped parasitic strips along with a Y-shaped stub have been used in the ground plane so as to obtain high isolation, which leads to a decrease of mutual coupling between the antenna elements. The proposed antenna achieves a wide impedance bandwidth of 7.1-22 GHz (106%) along with low mutual coupling of less than -15 dB within the entire frequency range as well as circular polarization characteristics, which covers the frequency range (-3 dB) of 7.1-7.9 GHz (10.6%). Thus the antenna can be considered as a potential candidate for modern wireless communication systems.

In this manuscript, the realization of penta-band notches with the aid of an ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna for diverse wireless applications is demonstrated. A single port UWB antenna is utilized to construct the proposed MIMO antenna, which comprises an altered patch loaded with three U-shape slots and an inverse U-shape slot on the feed line followed by a C-shape stub adjacent to the feed line. These slots and C-shape stub are liable to generate five notches at 3.4 GHz (3.16-3.67 GHz), 4 GHz (3.88-4.10 GHz), 4.6 GHz (4.56-4.75 GHz), 5.7 GHz (5.65-5.92 GHz), and 7.8 GHz (7.39-8.12 GHz), respectively. These notches depreciate interference from WiMAX, C-band, WLAN and X-band (satellite communication) frequencies. Alternatively, the reported antenna can also be utilized as a proximity radar (8-12 GHz) in X-band. The proposed antenna engraved on a Rogers RT/Duroid 5880 substrate having an overall size of 80 × 80 × 1.6 mm³ or 0.8λ₀ × 0.8λ₀ × 0.016λ₀ (λ₀ is the free-space wavelength at lowest frequency 3 GHz). Simulation and experimentation have been performed to corroborate the performance of the reported antenna. Results emphasize that the proposed MIMO antenna operates from 3 GHz to 14 GHz with measured peak gain 4.8 dBi, radiation efficiency above 82% and isolation less than -20 dB. Except at notches, the computed envelope correlation coefficient (ECC) is less than 0.03; diversity gain (DG) is approximately 10; total active reflection coefficient (TARC) is less than -10 dB; channel capacity loss (CCL) is less than 0.35 bps/Hz. These characteristics qualify it as a multifunctional antenna for wireless applications, lowering the antenna count needed in compact wireless devices.

In this paper, a single band two element MIMO antenna for future 5G wireless applications at 5 GHz is presented. The antenna consists of T over T shaped meander micro strip lines printed on the front side and defected ground structure on the back side of an RT Rogers 5880 substrate, which are able to excite a resonance mode. The antenna operates at 4900 to 5060 MHz (|S₁₁| < -10 dB) covering the 5G NR band n79. The antennas are to be placed symmetrically along the edges at the corners of the Smartphone panel. The isolation in the case of two elements MIMO antenna is enhanced by an I-shaped ground slot. The mutual coupling reduction is facilitated by 10 mm neutralization line (NL) at both hands. The prototype is fabricated to validate the proposed model. The measured results show good accordance with simulated results. The main performance results wherever possible of the proposed design are calculated, compared and analyzed with the measured results.

A transmissive single-layer Huygens unit cell based on induced magnetism is proposed to design low-profile and multi-focus metasurface. The Huygens unit cell consists of a pair of antisymmetric metal elements and a dielectric substrate with only 1.2 mm thickness (λ₀/6.8 at 37 GHz). The surface currents flowing in the opposite directions form the circulating electric currents to induce the magnetic currents orthogonal to the electric currents. The full coverage of 2π phase is achieved through optimizing the parameters of the metal elements, which solves the problem of the incomplete phase coverage caused by layer number reduction. With Holographic theory, the compensating phase distribution on the metasurface is calculated. The incident plane wave can be converged to designated points in any desired fashion including focal number, location and intensity distribution, which exhibits outstanding manipulation capability. As the simulations and measured results show, the designed metasurface can achieve good multi-focus focusing characteristics. The focusing efficiency at the center frequency is 43.78%, and the relative bandwidth with 20% focusing efficiency exceeds 20%. The designed metasurface has the advantages of low profile, simple processing, and high efficiency, which has a wide range of application prospects in the fields of millimeter wave imaging, biomedical diagnosis and detection.

We presented a miniaturized defected ground structure-based millimeter-wave (MMW) contemporary MIMO antenna for 5G smart applications devices. The proposed MIMO antenna offers many advantages including high gain, compactness, planar geometry, wide impedance bandwidth, and reduced mutual coupling effects performance. The top layer of the proposed four-port MIMO antenna design comprises 1x2 rectangular patch array structures, with each placed at the middle of a 20x20 mm² substrate of material (RO4350B) having thickness of 0.76 mm and loss tangent of 0.0037. For miniaturization and better performance, both the ground layer and radiating patches are defected with slots of a rectangular shape while an E-shaped slot is placed at the center of the ground plane. The operating impedance bandwidth of the proposed antenna ranges from 26.4 to 30.9 GHz incorporating the dominant portion of the mm-wave band. The proposed MIMO antenna is also characterized by the fundamental MIMO performance metrics such as Envelope Correlation Coefficient (ECC) which is less than 0.12 for any two-element array that encounters the mandatory standard of <0.5, high Diversity gain (DG) reaching its ideal value of 10 as well as minimum isolation of -19 dB with a total efficiency of 85% at 28 GHz. These characteristics make the proposed compact four-port MIMO antenna one of the best candidates to be used in 5G portable devices.

In this paper, impedance modeling is presented for analyzing the metallic loading effect on the performance of a split ring resonator (SRR) antenna in (2.4-2.5)/(5.1-5.8) GHz frequency bands. Two SRR antennas of rectangular and circular rings have been designed on ANSYS HFSS software, and their return losses are obtained as -16.63/-25.26 dB at 2.7/5.8 GHz and -10/-20.09 dB at 2.2/5.2 GHz, respectively. Then the metallic loadings are incorporated in both rectangular and circular SRR antennas, which move the peak resonant frequency to 2.5/5.1 GHz with simulated return losses of -14.39/-22 dB for rectangular SRR antenna and to 2.6/5.1 GHz with -17.64/-11.10 dB, respectively for circular SRR antenna. Then, to analyze the effect of metallic loading on SRR antenna performance, a set of equations are derived from the equivalent circuit of the SRR antenna without and with metallic loading to evaluate the lumped elements values. The circular SRR antenna with metallic loading is fabricated, and its measured return loss is found to be -17.94/-15.76 dB at 2.415/5.23 GHz. The lumped component values are calculated from the measured return loss using the derived equations, and these values are compared with those obtained from the simulated return loss for circular SRR antenna. A shift in resonant frequencies towards the desired bands is observed due to the inductive effect of the metallic loading. The axial ratio values higher than 15 dB confirm that the proposed SRR antennas with metallic loadings are linearly polarised. The 2D patterns in E-plane and H-plane, as well as 3D far-field patterns, confirm an omnidirectional radiation pattern for circular SRR antenna, which is useful for WLAN applications.

A wideband magneto-electric (ME) dipole with characteristics of dual-circular polarization is presented in this paper. The proposed antenna is composed of four horizontal radiation patches, four pairs of vertical radiation patches, a ground plane, a pair of wideband feeding networks, and novel crossed feeding structures which work as wideband 3-stage impedance matching transitions. The feeding networks which contain a Wilkinson power divider and a coupled-line phase shifter are printed on the bottom of the ground plane, and they can provide stable two-way output wideband signals with quadrature-phase. The proposed antenna works as a ME dipole with a wide operation bandwidth of 53.2% (S₁₁ < -10 dB, and Axial Ratio (AR) < 3 dB) from 1.71 GHz to 2.95 GHz for right-hand circular polarization (RHCP) and 62% from 1.7 GHz to 3.25 GHz for left-hand circular polarization (LHCP), respectively.

Novel microstrip single-band and dual-band bandpass filters (BPFs) are presented in this paper. Firstly, a pair of open-ended stubs of less than λ/4 in length is connected to a uniform impedance resonator (UIR) at two symmetrical positions with respect to its centre, and at the same time other two open-circuited stubs with different lengths are loaded in the middle of the resonator. By virtue of parallel-coupling structure at I/O ports, a single-band BPF is constructed centered at 2.2 GHz with 10.6% 3-dB bandwidth, and two transmission zeros are implemented at the right side of the passband. Next, the L-shaped I/O coupled lines are applied to suppress the inherent spurious response of the stubs-loaded resonator. As a result, a dual-band BPF with two passbands at 2.2 GHz and 5.2 GHz, which is self-contained with three transmission zeros between the two passbands, is constituted. Finally, the proposed bandpass filters are designed and fabricated to provide an experimental validation for the predicted performances.

This airticle provides a review of transfer function-based (TF-based) surrogate optimization for electromagnetic (EM) design. Transfer functions (TF) represent the EM responses of passive microwave components versus frequency. With the assistance of TF, the nonlinearity of the model structure can be decreased. Parallel gradient-based EM optimization technique using TF in rational format and trust region algorithm is introduced first. Following that, we review the EM optimization using adjoint sensitivity-based neuro-TF surrogate, where the neuro-TF modeling method is in pole/residue format. The adjoint sensitivity-based neuro-TF surrogate technique can reach the optimal EM responses solution faster than the existing gradient-based surrogate optimization methods without sensitivity information. As a further advancement, we discuss the multifeature-assisted neuro-TF surrogate optimization technique. With the help of multiple feature parameters, the multifeature-assisted neuro-TF surrogate optimization has a better ability of avoiding local minima and can achive the optimal EM solution faster than the surrogate optimizations without feature assistance. Three examples are used to verify the above three methods.

Compared to natural materials, artificial subwavelength structures can enhance chiroptical effects in a stronger way, and the requirement of low material loss and wideband operation is desired in many situations. Here, we propose an all-dielectric chiral metasurface as a periodic array of centrosymmetric staggered silicon cuboid pairs to achieve strong circular dichroism in a wide band. As a demonstration, the designed chiral metasurface may strongly reflect the chosen circularly polarized light with the spin preserved in the operating wavelength range of 1.51~1.60 um while highly transmit (with an efficiency greater than 95%) the opposite circularly polarized light with the spin flipped. Then, two application cases are given for the designed chiral metasurface. A flat chiral meta-lens is constructed to produce wideband focusing in the transmission/reflection side while the disturbing from the opposite circular polarization is well blocked by high reflection/transmission. A chiral Fabry-Perot cavity is also constructed, which has an extremely high quality factor (2.1E4). The proposed method provides an efficient way to produce strong chiroptical effects and has a promising potential for various applications such as signal processing, sensing, radiation and detection.

In this work, we investigate the feasibility of applying deep learning to phase synthesis of reflectarray antenna. A deep convolutional neural network (ConvNet) based on the architecture of AlexNet is built to predict the continuous phase distribution on reflectarray elements given the beam pattern. The proposed ConvNet is sufficiently trained with data set generated by array-theory method. With radiation pattern and beam direction arrays as input, the ConvNet can make real-time and fairly accurate predictions in milliseconds with the average relative error below 0.7%. This paper shows that deep convolutional neural networks can ``learn'' the principle of reflectarray phase synthesis due to their inherent powerful learning capacity. The proposed approach may provide us a potential scheme for real-time phase synthesis of antenna arrays in electromagnetic engineering.

In this paper, we present a waveguide-fed hollow cylindrical dielectric resonator antenna (CDRA) with dual-band operation and its modified structure for wider bandwidth and enhanced gain operation. The distinctive nature of the structure provides two bands having resonant frequencies at 8.46 GHz and 9.24 GHz with maximum gains of 5.37 dBi and 6.86 dBi respectively with a single dielectric resonator antenna (DRA). The dual-band is achieved due to the resonance of DRA and the air column inside it. Excellent coupling is achieved in both bands. The dual-band structure is modified by changing the volume of the air column inside the CDRA keeping all other parameters constant to result in a wider band and high gain antenna. A bandwidth of 7.9% with a resonant frequency of 9.0 GHz and a maximum gain of 8.14 dBi is obtained for the modified structure.

In this paper, the inversion method of mesospheric neutral wind is studied based on mid-latitude AgileDARN HF radar. Firstly, the meteor target observation method is carried out using 7.5 km range resolution and 2 s integration time. Then, the method of extracting the meteor echo from the data according to the doppler characteristics of the meteoris studied. Finally, the meridional and zonal components of mesospheric neutral wind are obtained by singular value decomposition method based on doppler velocity of meteor echo. The data analysis shows that the meteor echo has the highest incidence in the morning of local time and the lowest incidence in the evening of local time. The semi-diurnal characteristics of tidal waves can be seen from the meridional and zonal components of mesospheric neutral wind. Aiming at the ambiguity of elevation angle measured by AgileDARN HF radar, a method is proposed to reduce the ambiguity of elevation angle, and the wind field profile of mesospheric neutral wind along altitude is obtained, which lays a foundation for the subsequent study of gravity wave, tidal wave and planetary wave based on mesospheric wind field.

This research introduces a novel design of a metamaterial absorber having the range in terahertz, capable of sensing changes in the refractive index of the encircling medium. The layout includes adjoining rectangular patches in the form of a plus symbol along with four circular patch resonators (CPRs) on the pinnacle of a Gallium Arsenide (GaAs) substrate. The proposed design comes up with three consecutive absorption peaks, with an absorptivity of 99.0%, 99.75%, and 98.0% at three different resonant frequencies of 2.36 THz, 2.675 THz, and 2.97 THz, respectively, and a Full Width Half Maximum (FWHM) of 0.08, 0.04 and 0.05. This structure's quality factor (Q-factor) at the three resonant frequencies is 29.5, 66.8 and 59.4 together with 6.75, 17.5 and 30 as figure of merit (FoM), respectively. The proposed design offers a sensitivity of 0.54 THz/RIU, 0.7 THz/RIU, and 1.5 THz/RIU in those three absorption bands. To support the selection of design parameters, parametric assessment was done. The designed sensor can find its applications in terahertz sensing.

This paper presents a MIMO antenna system composed of eight wideband horizontal dual-loop antenna elements. Each dual-loop antenna is printed on both sides of a smartphone board. The unit element antenna is designed to operate in the frequency range from 3.2 GHz to 5 GHz. The performance of the MIMO system is then analyzed. The performance of the obtained MIMO system in the frequency range from 3.2 GHz to 4.8 GHz is characterized by input reflection coefficient which is less than -6 dB for all antenna elements, and the isolation between the elements is larger than 15 dB. The total efficiency is greater than 55% over the entire band (3.2-4.8 GHz). Parameters of the multichannel antennas including envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CLL) are analyzed to evaluate the performance of the MIMO system. The effect of the human hand and head on the performance of this MIMO antenna is also investigated. In addition, the effect of the radiated fields on the human body is also studied. The Specific Absorption Rate (SAR) value is found to be less than 0.8 W/kg. The MIMO system antenna is fabricated and measured. Good agreements are obtained between the simulated and measured parameters. The proposed MIMO system is applicable to the 5G N48, N77, and N78 bands.

We present a capacitive wireless power transfer (C-WPT) system using rotating capacitors for wireless sensor system (WSS) on propulsion shaft. In order to supply stable power to the WSS consisting of four sensors, a controller, and a radio module, we designed the rotating capacitor connected in parallel with multiple plates that minimizes the change in capacitance of the power coupling capacitor of the C-WPT system. A Class-E converter and transformers topology are utilized to drive the C-WPT system for WSS. The fabricated C-WPT system transmitted stable power even when the rotational speed of the shaft was changed from 100 to 300 revolution per minute (rpm), and achieved power of 20.48 W and transmission efficiency of 64.29%.

Complex reservoirs such as fresh-water formations and water-flooded reservoirs developed by water injection have complex electrical characteristics owing to the influence of formation water salinity. It is difficult to accurately evaluate and identify the fluid in such complex reservoirs by using the conventional resistivity method. However, the water salinity of the formation has a reduced effect on its dielectric constant; therefore, dielectric logging technology can be used to effectively identify fresh-water formation and evaluate the water-flooding level of the water-flooded layer. The accuracy of the formation response inversion charts of dielectric logging instruments is important for accurately evaluating fluids in complex reservoirs when these instruments are used. This study proposes a full-wave simulation method based on Maxwell's equations and the engineering parameters value of the dielectric logging instrument. The formation response conversion charts of the dielectric logging instrumentare accurately calculated and can be used in practical logging; the simulation results are compared with those obtained using an equivalent magnetic dipole model; Based on the accurate simulation of the formation response of the dielectric logging instrument, a high-frequency dielectric logging instrumentis developed, and it is applied to the fresh-water formation and water-flooded layer in the Nanyang and Ordos Basins.

This paper introduces a reconfigurable polarization MIMO (Multi-Input Multi-Output) dielectric resonator antenna at millimeter-wave frequency band. The proposed antenna consists of four single dielectric resonator antennas that are placed in 2×2 configuration to form a MIMO antenna, and also this design is based on using the pin diode switching concept to control the antenna polarization. In order to modify the antenna structure for different polarizations, two pin diodes are used in the ground place of the MIMO antenna. The designed antenna operates at 4.35 GHz for polarization diversity applications of the modern wireless MIMO systems. The proposed antenna covers a bandwidth of 11.26% at the central frequency and provides circular and linear polarizations with high gain around 6.4 dB. The antenna performance in terms of reflection coefficient, gain and axial ratio bandwidth in different modes (ON-ON, ON-OFF, OFF-ON and OFF-OFF) is measured. The advantages of the designed antenna are simple structure (using two pin diode switches to modify antenna polarization), high gain, low profile, and light weight. According to the measurement and simulation results, the designed antenna displays good return loss and radiation performance. Using the plexiglass as an antenna material which is very cheap and available in different dimensions is another advantage of the proposed antenna which reduce the fabrication cost.