In this paper, a novel miniaturized circularly polarized (CP) antenna for BeiDou Satellite Navigation System (BDS) applications is presented. The proposed antenna is composed of three substrates with the same size, which are combined by four shorting pins. Parasitic strips are used to reduce the size, and the radiation patch is fed by two coupling feeding patches with the same amplitude and 90° phase difference. The overall dimension of the proposed antenna is only 18 mm x 18 mm x 23.5 mm (about 0.08λ₀ x 0.08λ₀ x 0.1λ₀), and its weight is about 25 grams. The performance study with different geometric parameters has been conducted. A prototype based on optimized dimensions has been fabricated and measured, and the tested results exhibit a good impedance matching bandwidth ranging from 1.2 to 1.35 GHz centered at 1.268 GHz. This antenna also has stable hemispherical radiation patterns and good CP characteristics. Good agreement between analytical and experimental results is obtained.

Theoretical investigation of optical properties of a metallic sphere coated with uniform layer of anisotropic dielectric material is conducted by studying its polarizability, scattering cross section, absorption and extinction cross section. The dispersive characteristics of metal (tungsten/silver/gold) are mathematically modeled through well known Lorentz-Drude model. A detailed analysis of the behaviors of polarizability, scattering cross-section, absorption and extinction cross section is carried out for different specific values of the radius and components of the tensor permittivity. The impact of variation of different parameters on location and magnitude of the surface plasmon resonance is highlighted.

A low-profile dual-band composite structure antenna is proposed for fifth generation mobile communication system (5G), which is named as Antenna on Antenna (AOA). Loaded with an artificial magnetic conductor (AMC) reflector, the proposed AOA element consists of a pair of dual-polarized lower band (LB) dipole antennas working in the 0.7-1.03 GHz band and four upper band (UB) patch antenna arrays working in the 24.25-27 GHz band, which covers LTE and 5G millimeter wave band. In order to reduce the size of base station antenna, the millimeter wave patch antenna arrays are parasitic on the LB dipoles. While the radiator of the LB antenna is utilized as the ground of the millimeter wave patch antenna array, LB and UB antennas share the same dielectric substrate. The profile height of the antenna is reduced by AMC reflector effectively. Meanwhile, the three-element AOA array loaded with AMC reflector is designed to validate the overall performance of base station antenna. The operation bands of the proposed AOA are 0.7-1.03 GHz (S_nn<-14 dB) and 24.25-27 GHz (S_nn<-10 dB) for the LTE and 5G millimeter bands respectively. Antenna prototype was fabricated and measured to verify the design solution. The measured results which are consistent with simulated results show that the AOA has good impedance matching, port isolation, and stable radiation pattern.

A planner geometry triple-band circularly polarized (CP) antenna is proposed for wireless applications. The antenna consists of rectangular strips on the upper surface along with rectangular slots on the ground plane. The 3dB axial-ratio of the antenna is achieved through a reformed ground plane. Through the aid of these features, a small, compact wideband circularly polarized antenna is fabricated with an area of 25×25×1.02 mm³. The -10 dB impedance bandwidth of the proposed antenna is 8.2% (2.4-2.58 GHz), 33% (3.2-3.9 GHz), and 41.1% (5.2-7.8 GHz). While the 3-dB axial ratio bandwidth achieved by the proposed antenna is 89.7% (2.17-5.8 GHz). The designed antenna is suitable for wireless applications such as WiMAX, WLAN, ISM, Bluetooth, and Wi-Fi.

A novel conformal dielectric resonator antenna (DRA) array based on aperture-coupled series-feeding approach is presented for wireless communication. The antenna is composed of eight curved width-gradated DRA elements with a simple feeding structure. The proposed design presents a tapered current amplitude distribution by using DRA element width gradation method, and low side-lobe level (SLL) characteristic can be obtained. Besides, an extra matching line is inserted into the single feeding line to realize better impedance characteristic. To validate the performance of the proposed design, the conformal array is fabricated and measured in an anechoic chamber. The measured impedance bandwidth (|S₁₁|<-10 dB) of the fabricated prototype is from 5.65 GHz to 5.9 GHz. At 5.8 GHz, the antenna offers a measured peak gain of 14.75 dBi and SLL of -19.8 dB. The polarization discriminations of the array on E- and H-planes are greater than 20 dB. The measured results of the fabricated prototype demonstrate that the proposed design has the potential to be applied to wireless communication system with curved surface.

In this study, 1D Photonic Crystal (PhC) with Nematic Liquid Crystal (N-LC) central microcavity is analyzed and discussed using Rigorous Coupled Wave Analysis (RCWA) method. A microcavity is inserted into the 1D PhC by the Air Defect, making it ideal for measuring the properties of an N-LC contained inside the microcavity. Here simulation is considered for N-LC (E7) as a thermal sensor. The principle of photonic crystal thermal sensor operation is studied in the TE mode of the incident beam. We conduct a detailed study of the thermal sensor with differences in the width of central microcavity of N-LC. The sensitivity and quality factor are evaluated. Compared to other photonic crystal sensors mentioned previously, this thermal optical sensor has a much simpler structure and higher sensitivity.

Characterization of some biological materials relies on absorption imaging. In this paper, a highly translucent flat two-layer structure as part of an imaging system called spectrometer is proposed that has a very high numerical aperture (NA) and high quality factor (QF). The structure can be used to identify micro-biological materials with previously known absorption rate, under single-wavelength electromagnetic absorbance imaging. The proposed two-layer structure is composed of a double-near-zero (DNZ) slab coupled to a high-index dielectric slab with a specific thickness. In DNZ materials, both the permittivity and permeability are close to zero. The DNZ slab operates as a flat lens, and the very high-index dielectric slab functions as a high QF monochromator that at the same time increases NA of the lens without affecting translucidity of the two-layer structure. At the end, a transformation optics (TO) based nonlinear lens is introduced that can be replaced as the DNZ layer. The focus of the nonlinear lens can be tuned by tuning its material parameters.

Rectangular grid antennas are widely used in practice due to their advantages and versatility. This paper simplifies the design procedures of such antennas by optimizing their radiation characteristics using minimum number of the optimized elements while maintaining the same performance. The method consists of partitioning a fully square grid array into two unequally sub-planar arrays. The first one contains the inner and the most central elements of the initial planar array in which they are chosen to be non-adaptive elements, while the remaining outer and boundary elements which constitute L number of the square-rings are chosen to be adaptive elements. Then, the optimization process is carried out on those outer rings instead of fully planar array elements. Compared to a standard N×M planar array with fully adaptive elements, the number of optimized elements could be reduced from N×M to 2{2L(N-L)}, so as to significantly reduce the system cost without affecting the overall array performance. Results of applying the proposed method to optimize a small 9×9, medium 20×20, and large 40×40 size planar arrays with various values of L are shown.

Compared with the conventional coaxial magnetic gear, magnetic harmonic gear (MHG) is a device with large transmission ratio. In order to improve the transmission torque, an MHG with double fan-shaped Halbach arrays is proposed in this paper. According to the theory of magnetic field modulation and the unique unilateral effect of Halbach array, both inner and outer permanent magnets (PMs) are arranged in a Halbach array. In addition, all PMs are fan-shaped. The air gap magnetic field and torque of MHG are analyzed by two-dimensional finite element method. Compared with the conventional MHG, the proposed MHG enhances the air-gap magnetic flux density, reduces the air-gap harmonic content, and increases the torque density.

In this paper, a four-port compact active duplexer based on a complimentary split ring resonator (CSRR) and interdigital loaded microstrip coupled lines (CSRR-IL MCL) is presented. Interdigital capacitor is used on the top layer of the proposed structure and CSRR transmission lines are used on the bottom layer of the coupled lines in order to increase the coupling of the proposed circuit and create triple band resonances, respectively. The proposed active duplexer has one input port and three output ports operating in three distinct operation frequencies which are 1.4 GHz, 1.8 GHz, and 3.2 GHz. The active duplexer is designed to target LTE applications which are prevalent among the new technologies and devices. The input signal is split in terms of frequency into the three designed frequencies and is amplified by 13 dB gain of the amplifiers placed at the output ports. The fractional bandwidths of the proposed structure at 1.4 GHz, 1.8 GHz, and 3.2 GHz are 5.2%, 2.8%, and 9.4%, respectively. It is worth mentioning that the size of the proposed active duplexer is 0.29λ₀×0.38λ₀. The design guide of the proposed structure is presented, and it will be shown that the simulation as well as the measurement results of the proposed active duplexer have an acceptable agreement with each other. It should be noted that the VSWR of the proposed structure is less than 1.5 which means that the active duplexer has low return loss, and it is the plus point of it.

A novel 4-element MIMO (multi-input multi-output) array antenna is proposed for DSRC, WLAN, and X-band applications. The proposed antenna is a microstrip antenna that consists of a simple square patch as radiating element with a defected ground structure (DGS). Dimensions of the proposed antenna are very compact with size 40 x 48 x 0.8 mm³. It operates from 5.6-6.1 GHz (DSRC/WLAN) and 8.7-10.8 GHz (X-band) with impedance bandwidths (S₁₁ < = -10 dB) of 500 MHz and 2.1 GHz, respectively. The isolation between elements of MIMO is also greater than 25 dB in the operating bands. Antenna performance parameters are investigated at 5.9 GHz and 10.5 GHz center frequencies and computer-simulated, and experimentally measured characteristics are found to be satisfactory. A peak gain of 4.8 dB is achieved, and radiation efficiency is also greater than 75% in operating bands. ECC (Envelope Correlation Coefficient) is less than 0.05, and DG (Diversity Gain) is very close to 10. Group delay among the MIMO elements is below 2.7 ns, and CCL (Channel Capacity Loss) is also below 0.4 bits/sec/Hz. Therefore, the proposed 4-element MIMO antenna is suggestible for DSRC/WLAN and X-band applications.

A low-profile, electrically compact, and cost-effective antenna for wireless communication is presented. The antenna comprises self-complementary dipole elements on each side of the resonator surface. The dipole is excited using co-axial feed for an efficient impedance matching. An electrically compact antenna has dimensions of 0.13λ × 0.26λ at the lower frequency. The dipole covers 1.57 GHz and 3.65 GHz frequencies offering the measured impedance bandwidth in the order of 1.83% and 2.30% respectively. The self-complementary structure of the dipole having multiple coupling elements permits adequate tuning of the antenna on target frequencies. The resonant modes of the antenna can be tuned by merely modifying the position of the complementary structure on each side of the dipole. The engineered slots in the dipole permit further fine-tuning. The antenna presents gain in the order of 0.71 dBi and 1.27 dBi and stable radiation patterns for the two frequencies.

We propose single/dual circularly-polarized (CP) antennas based on reflective metasurfaces with cross-polarization conversion. By suspending a probe-fed printed bow-tie dipole or a crossed bow-tie dipole above the reflective polarization-conversion metasurface and appropriately tuning the distance between them, a single-CP or a dual-CP antenna is generated. The theoretical design principle on this novel CP antenna structure has been discussed. Simulations and experiments are conducted to validate the design principle. The measured results show that the proposed single-CP antenna has achieved a 3-dB axial ratio (AR) bandwidth of 8.0%, from 12.67 to 13.72 GHz, and a peak gain of 8.03 dBi, while the dual-CP antenna exhibits a dual-CP AR bandwidth of 7.1%, from 13.09 to 14.05 GHz, and peak gains of 8.49 dBi and 7.03 dBi for left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP), respectively. The measured isolation between the two ports of the dual-CP antenna is less than -20 dB. The operating frequency of the proposed antennas can be easily scaled to other frequencies that are applied to some specific wireless applications.

In this letter, a novel design of independently reconfigurable upper and lower bands of a Yagi-Uda antenna is presented. The reconfiguration approach used in this antenna is based on keeping either the upper or lower band edge fixed with gradually increasing the bandwidth to the lower or upper ones. In this system, PIN diodes are used to control the length of the resonator and the slot-line of Yagi-Uda antenna to achieve upper and lower bandwidths limit reconfigurability. An antenna prototype was fabricated and tested in order to validate the design approach of the bandwidth reconfiguration. The proposed antenna has several different modes of operation with capability of tuning the fractional bandwidth (FBW) from 7% to 33% and 18% to 72% when using resonator and slot-line, respectively. This antenna can be a good candidate for cognitive radio applications that need adjusting the frequency bandwidth.

This research letter offers a generalization character to our previous work [4, 5] to examine a 3-D almost periodic phased array antenna excited by arbitrarily located sources. An original modal formulation based on the Floquet analysis procedure is proposed utilizing the periodic walls along x, y, and z-axes, where the analysis region in the spectral domain is reduced to the Brillouin zone. Here, a good idea is provided to enforce the given boundary conditions for obtaining an integral equation formalism developed through Galerkin's method for solving periodic volumic structure (e.g. 3-D regular structure in the cubic grid). The interaction between cells in 3-D geometry (lattice) could be deduced using a novel expression of mutual coupling. However, it is possible to obtain it explicitly by the mean of Fourier transform and its inverse. Then, it is proven how Floquet analysis can be employed to study a 3D-finite array configuration with arbitrary amplitude and linear phase distribution along x, y, and z directions, including mutual interaction effects. To deal with the real hole 3D array configuration, a superposition theorem is suggested to describe the electromagnetic behavior in the spatial domain. For modeling the given 3D antenna array, one numerical method is adopted: The moment method combined with an equivalent circuit (MoM-GEC). An important gain in the running time and memory used would be achieved using Floquet analysis in comparison with other spatial conventional methods (especially, when the number of cells increases by adding the second and third directions).

In the simulation of high frequency nanoscale semiconductor devices in which electromagnetic (EM) fields and carrier transport are coupled, and optoelectronic devices in which strong interactions between EM fields and charged particles exist, both the Maxwell's equations and the time-dependent Schrödinger equation (TDSE) need to be solved to capture the interactions between EM and quantum mechanics (QM). One of the numerical simulation methods for solving these equations is the finite difference time domain (FDTD) method. In this review paper, the development of FDTD method applied in EM and QM simulation is discussed. Several widely used FDTD techniques, i.e., explicit, implicit, explicit staggered-time, and Chebyshev methods, for solving the TDSE are introduced and compared. The hybrid approaches based on FDTD method, which are used to solve the Poisson-TDSE and Maxwell-TDSE coupled equations for EM-QM simulation, are also discussed. Furthermore, the applications of these simulation methods for nanoscale semiconductor devices and optoelectronic devices are introduced. Finally, a conclusion is given.

In order to solve the problem that the unbalance vibration caused by rotor mass eccentricity of the six-pole radial hybrid magnetic bearing (HMB) seriously affects stability and security of the system, a feed-forward compensation control strategy for rotor unbalance vibration based on fuzzy least-mean-square (LMS) algorithm is proposed. Firstly, the structure, operation principle and mathematical model of the six-pole radial HMB are introduced, and the cause of rotor vibration is analyzed and the dynamic equation of rotor deduced. Secondly, an LMS self-adapting filter is improved by using a fuzzy inference system, and the step size of the LMS algorithm is combined with the fuzzy control theory. By using the Takagi-Sugeno (TS) fuzzy inference machine system to adjust the step size of the algorithm, the filter output can approach the unbalance vibration signal smoothly and quickly, and realize the vibration compensation of the rotor. Finally, the simulations and experiments are carried out to verify that the proposed method can not only effectively suppress the unbalance vibration of the six-pole radial HMB rotor in real time but also have good compensation accuracy. The results show that the vibration compensation effect of fuzzy LMS algorithm is better than that of fixed step size filtering algorithm.

In the paper, a filtering coupled-line trans-directional (CL-TRD) coupler with broadband bandpass response is presented for the first time. It is composed of three sections of coupled lines, four transmission lines and four shunt stubs. Design equations of the proposed filtering CL-TRD coupler are derived using the even- and odd-mode analysis. For demonstration, a prototype operating at 2.4 GHz is designed, fabricated and measured. Under the criterion of |S₁₁| < -10 dB, the measured bandpass bandwidth is 41.7 %. In this bandwidth, the output port phase difference is within 90° ± 5°. Besides, two stopbands (0.91 GHz ~ 1.89 GHz and 3.36 GHz ~ 4.3 GHz) are obtained on both sides of the passband with sharp rejection. The measurements and comparisons results show that smaller size, wider bandwidth and easier fabrication than the reported filtering couplers are exhibited by the proposed filtering CL-TRD coupler. It indicates that a good candidate for filtering-coupling applications can be served by the proposed coupler.

Anomalous dispersion region is a resonance signature in the frequency response of resonators known as Lorentz resonators. It is identified by two consecutive slope reversals of the transmission phase response and a dip in the amplitude response. In this letter, we propose to exploit this unique resonant phase signature in characterization of the conductivity of solid and liquid material samples. The microwave resonator sensor consists of an open microstrip stub whose conductivity is designed to vary in response to an intruding sample. The transmission response of the resonator containing the material sample is measured using a vector network analyzer. The change of conductivity affects the Q-factor which can be detected by either the slope changes of the anomalous dispersive phase or the 3dB bandwidth of the amplitude spectrum. The hypothesis is practically demonstrated by detecting resistive changes of a saline solution whose conductivity depends on the amounts of additive salt.

This article present a synthesis modelling of isolation in a diamond-shaped fractal electromagnetic band gag (DSFEBG) based two-port multiple input and multiple-output (MIMO) antenna using the Gaussian Process Regression (GPR). A compact two-port MIMO antenna with 0.140λ inter-element spacing is considered for isolation improvement. To predict mutual coupling in two-port MIMO antenna supervised learning-based regression technique of GPR, the model is trained with 50 samples and tested on 125 samples. The model performs result prediction in less than 1 second with RMSE less than 0.0001%. For a better understanding of the isolation between elements of the MIMO antenna, the automatic relevance determination property of GPR is presented. The proposed model does faster computation and is efficient in predicting isolation in DSFEBG based antennas for lower and high-frequency bands of 5G communication system.