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.

To meet the requirements of miniaturization, multi-functions, and anti-interference of the antenna, this paper proposes a compact dual notch band frequency reconfigurable ultra-wideband (UWB) antenna. The antenna consists of an angle-cut rectangular radiation patch, a coplanar waveguide (CPW) structure, and a defective ground structure (DGS). A C-slot and an inverted U-slot are introduced to eliminate the interference of the Indian National Satellite band (INSAT), 5G band, and X satellite communication band. By controlling the PIN diodes across the two slots, the antenna can work in four states: UWB, two single notch bands, and one dual notch band. The impedance bandwidth in UWB mode is 2.9-12 GHz, with a relative bandwidth of 122%. The notch frequencies are 4.2-5.2 GHz and 6.2-8.1 GHz, respectively. In the passband of the antenna, the maximum gain is 7.17 dBi, and the group delay is less than 1 ns. The antenna size is 18 × 17 × 1.6 mm³, which is easy to integrate with the communication systems. The antenna can be freely switched between the UWB mode and each notch band mode, which can be applied to the UWB wireless communication systems.

A multi-input multi-output (MIMO) antenna system is presented for wireless devices operating at WLAN (2.45, 5.25, and 5.775 GHz) bands. Each of the two antennas in the MIMO system consists of a crescent-shaped monopole whose first part covers the 2.45 GHz band while its second part covers the 5.25 GHz and 5.775 GHz bands. The second part of the monopole is a slot etched in the protruded ground plane between the two antennas. A decoupling mechanism in the form of two interlaced ring-shaped slots is used. The proposed MIMO antenna system is designed on an FR4 substrate with overall dimensions of 40x47.5x1.5 mm and a small edge-to-edge spacing of 7.3 mm between two antennas. According to the measured results, the proposed design covers two frequency bands (2.2-2.83 GHz and 5.03-5.95 GHz) and has a mutual coupling of -20.78 dB at 2.45 GHz and -42.65 dB at 5.55 GHz. The proposed antenna's performance in both simulations and testing indicates that it is a good choice for WLAN applications.

Confining electromagnetic (e-m) modes in a tiny space is a desirable aspect for many applications including targeted material heating and light harvesting techniques. In this work, we report spatially squeezed e-m modes of a cavity resonator formed by the modified transformation optical (TO) medium. The proposed coordinate transformation scheme suggests curved contours of refractive index profile such that the e-m mode can be confined within the contours. The effective mode area for a TO cavity is at least 10 times smaller than the air-filled metallic cavity. The confined e-m modes of a proposed cavity are horizontally flattened but vertically squeezed of the dimension of λ/49. The material parameters of the proposed TO medium are approximated with non-magnetic and isotropic dielectric values. For an application aspect, squeezed mode of the TO cavity is used for targeted material heating, and it is demonstrated based on e-m thermal co-simulations. A tiny dielectric material placed at the squeezed part of the cavity mode is heated rapidly with the temperature rise of 2.350˚C/s (110˚C/s) for the single (dual) e-m source excitation with the peak electric field strength of 5 x 10⁴ V/m. We further discuss how one can realize the proposed TO medium practically with a cell-grid approximation using photonic crystals and metamaterials.

A novel dual-polarized printed AMOS antenna with high isolation operating at 5.4 GHz is proposed. The horizontal and vertical polarizations have similar radiation patterns in horizontal plane with the HPBW over 90°. In the frequency range of 5.2 GHz-5.6 GHz, the vertical polarization antenna and horizontal antenna have the gain above 7.4 dB and 10 dB, respectively. The S₂₁ between the two input ports of the dual-polarized AMOS antenna is lower than -40 dB.

We study electromagnetic wave propagation in a system that is periodic both in space and in time, namely, a discrete (``lumped'') transmission line with capacitors (``varactors'') that are modulated in time harmonically. These periodicities result in exotic electromagnetic band structures that are periodic in the angular frequency ω and in the phase advance ka of the wave. Depending on the strength of modulation m and the reduced modulation frequency Ω/ω₀ (where ω₀ is the resonant frequency of a unit cell of the transmission line), this band structure can display frequency or wave vector band gaps, both, or neither. Moreover, minor changes in or the modulation strength can control the aperture or closure of a gap and even transform a k-gap to an ω-gap. Such phase transitions are intimately associated with exceptional or critical points in the (ω, k, Ω, m) space.

In this letter, a new bandpass frequency selective surface (FSS) with sharp sidebands is proposed to suppress electromagnetic interferences caused by the fifth generation (5G) mobile communication to fixed C-band satellite system. The proposed design is composed of three cascaded layers separated by air space, whose unit cell geometry comprises metal square loops, square slots and their evolvement. As the overall configuration yields high-order bandpass characteristics with multiple transmission poles and zeros, a flat passband covering 3.7-4.2 GHz is obtained, while the out-of-band shielding effectiveness mostly remains better than 20 dB over frequency lower than 6.5 GHz. Good angular stability and polarization independency are also achieved due to structural symmetry. A prototype was fabricated and measured, whose results agree well with the full-wave simulation.

Non-Hermitian skin effect denotes the exponential localization of a large number of eigen-states at boundaries in a non-Hermitian lattice under open boundary conditions. Such a non-Hermiticity-induced skin effect can offset the penetration depth of in-gap edge states, leading to counterintuitive delocalized edge modes, which have not been studied in a realistic photonic system such as photonic crystals. Here, we analytically reveal the non-Hermitian skin effect and the delocalized edge states in Maxwell's equations for non-Hermitian chiral photonic crystals with anomalous parity-time symmetry. Remarkably, we rigorously prove that the penetration depth of the edge states is inversely proportional to the frequency and the real part of the chirality. Our findings pave a way towards exploring novel non-Hermitian phenomena and applications in continuous Maxwell's equations.