We propose a compact wideband planar quad-element multiple input, multiple output (MIMO) antenna, which can cover a wide bandwidth ranging from 2.2 to 30 GHz. Novel reversed S-shaped walls provide high isolation between antenna elements within an extremely closed space, with the edge-to-edge distance between elements being only 1 mm. The simulated and measured results with respect to S parameters and radiation patterns are in good agreement. The experimental results indicate that the quad-element MIMO antenna can provide wide bandwidth (2.2-30 GHz), high isolation (with the transmission coefficients below -19 dB), and low profile (only ~λ₀/40) within a compact structure (32 mm ×32 mm×4.5 mm). This compact wideband quad-element MIMO antenna with high isolation and low profile has important applications in mobile devices or other small-scaled equipment in future 5G communication.

Based on the extended Huygens-Fresnel principle, the expressions of degree of coherence, ellipticity, and beam wander of multi-Gaussian Schell-model beam through the anisotropic turbulence are derived. Their statistical properties in anisotropic turbulence are illustrated numerically. The results show that the beam width and beam wander of multi-Gaussian Schell-model beam decrease with the increase of the mode order or the decrease of the turbulence structure parameter and initial coherence and that the degree of coherence of multi-Gaussian Schell-model beam decreases with the increase of the turbulence structure parameter or the decrease of the mode order. Furthermore, the beam wander of multi-Gaussian Schell-model beam is smaller than that of Gaussian Schell-model beam under the same conditions.

In this paper, complementary split ring resonator (CSRR) based single feed rectangular microstrip antennas are designed for circular polarization. In the first antenna design, two CSRRs are loaded on ground, and for the second design, two CSRRs are loaded on patch with identical orientation of meta-resonators in both cases. CSRRs are used to diminish the resonance frequency of the antenna, and thus the antenna size miniaturization can be achieved. Overall dimensions of the two antennas are (50×50×1.6) mm³, and the impedance bandwidth for S₁₁ < -10 dB exhibits between 2.3 and 2.4 GHz which is useful for wireless communication service. The characteristics of the proposed antennas, i.e., reflection coefficient, axial ratio, gain, and radiation patterns, are observed and compared for the two cases. The proposed two antennas have been designed and simulated using CST Microwave studio 14. Measured reflection coefficient, gain, and radiation pattern are in good agreement with the simulated result.

Space-time antijamming problem has received significant concern recently in global navigation satellite. Space-time null widening technique is an effective technique to suppress interference signals in the case of rapidly moving environments. However, the computational complexity of traditional null widening algorithms is usually so high that it is difficult to apply in engineering problems. In order to solve this problem, a novel null widening algorithm based on multistage wiener filter (named as MWF-NW algorithm) is proposed for reducing the computational complexity of space-time antijamming algorithms. By using the Hadamard product and Khtri-Rao product, the space-time covariance matrix taper problem can be transformed into a space-time data taper problem. Then, the dimension of the tapered data is reduced by multistage wiener filter theory, and the optimal weight vector is also given by multistage wiener filter theory. Thus the algorithm can reduce computational complexity significantly and suppress interference signals effectively when the receiver is shaking. Simulation results are presented to verify the feasibility and effectiveness of the proposed algorithm.

When method of moments (MOM) is applied to calculate electromagnetic scattering problems of the linear structures, traditional basis functions such as RWG functions are unable to satisfy the requirements of numerical discretization, so linear basis functions are constructed to discrete line structures, To avoid direct calculation of dense impedance matrix equation, compressed sensing (CS) in conjugation with appropriate transformation is introduced. Firstly, the impedance matrix equation is operated to obtain an alternative equation in transform domain. Secondly, CS is used to form an undetermined equation to be solved, under the theoretical framework of CS, and the underdetermined equation can be solved by reconstruct algorithm ​but not iterative approach. Finally, numerical simulations of single wound axial mode helical antenna and four element linear antennas array are discussed to demonstrate the efficiency and accuracy of the proposed method.

In this paper, the electromagnetic scattering properties due to periodical configurations consisting of planar optical waveguides completely surrounded by a fluid media, in gaseous or liquid phase, are analyzed. In this new design, fluid separates the consecutive optical waveguides and it is also the common cover for all of them, thus significantly increasing the effect of the fluid on the evanescent field. This new configuration is designated as fluidic segmented optical waveguides. The theoretical algorithm was developed and recently updated by the authors, and it is based on the generalized scattering matrix concept, together with the generalized telegraphist equations formulism and modal matching technique. We present the first theoretical results concerning to these periodical structures with a fluidic common cover. To carry out the simulations, with the purpose to manufacture these devices in the future, glass and polymer were chosen as materials for the optical waveguides substrate and for enclosing the fluid as common cover medium, respectively. The spectral results obtained for the module and phase of the reflection and transmission coefficients have shown great sensitivity of the new proposal to the variations of the refractive index of the fluid, making it very attractive for the design of refractive index sensors and optical biosensors.

In this paper, a reconfigurable impedance matching network (RIMN) based on PIN diode is presented. RIMN is an impedance matching circuit containing only one matching stub embedded with one PIN diode. It can match two different load impedances under different biasing of the PIN diode. The RIMN has a very simple structure, and the parameters in the structure are easy to be calculated with a simplified solution method. During the solving process, the parasitic parameters of PIN diode are taken into account. For verification, a RIMN working at 5.8 GHz is designed and fabricated. The measured insertion losses for different load impedances are less than 0.4 dB with reflection coefficients less than 30 dB at the targeted frequency. Simulation and measurement show that the proposed RIMN has good performance.

A dual-band balun with inherent impedance transformation is presented in this paper. The inherent impedance transformation ratio from a range of 0.4 to 4.0 makes the balun ideal for the on-chip fabrication. The proposed dual-band balun exhibits excellent input port matching, equal output signal with phase dierence of 180, and extremely good isolation and matching at the output ports. A table is provided with the design parameters at the extreme impedance transformation ratios. The design concept of the proposed balun has been validated through a prototype fabricated on a Rogers RO5880 substrate. The measurement results are in good agreement with the EM simulation measurements.

In this paper, a hierarchical ultra-wideband characteristic basis function method (HUCBFM) is presented for high-precision analysis of wideband scattering problems. Unlike existing improved ultra-wideband characteristics basis function method (IUCBFM), HUCBFM reduces the number of characteristic basis functions (CBFs) necessary to express a current distribution. This reduction is achieved by combining primary CBFs (PCBFs) with the secondary level CBFs (SCBFs) to form a single hierarchical ultra-wideband characteristic basis function (HUCBF). As HUCBF incorporates the effects of PCBFs and SCBFs, the accuracy does not change significantly compared to that obtained by IUCBFM. Furthermore, the efficiencies of constructing the CBFs and filling the reduced matrix are improved. Numerical examples verify and demonstrate that the proposed method is credible both in terms of accuracy and efficiency.

In this paper, awideband dual-polarized multi-dipole antennawith a compact radiator size is developedfor 2G/3G/LTE base station applications. The original antenna is composed of a pair of crossed square loop dipoles (SLDs) and two big Y-shaped feeding lines. Thanks to the adopted capacitive coupling, a wide impedance bandwidth is obtained with dual resonant modesin the low and middle frequency bands. Owing to the circular chamfersin thecrossed SLDs, the dual resonant modes are away from each other. Thus, a compact radiator size is implemented, and it is about 0.382λ₀×0.382λ₀ (λ₀ is the wavelength at center frequency of operation). To further widen the operating bandwidth of the antenna, a pair of crossed rectangular loop dipoles (RLDs) and four small Y-shaped feeding lines are introduced to generate a new resonant mode at high frequency. As a result, the impedance bandwidth of the proposed antenna is enhanced.Based on the optimized dimensions of the simulated antenna model, a prototype is developed, fabricated and tested. Measured results show that the proposed antenna has a relative impedance bandwidth of 53.9% from 1.68 to 2.92 GHz at two ports for VSWR<1.5. Within the operating impedance bandwidth, the measured port-to-port isolation is better than 30 dB. In addition, a stable gain of 8.2±0.5 dBi and a stable radiation pattern with 66°±4° half-power beamwidth (HPBW) in the horizontal plane are achieved across the whole bandwidth of operationfor dual polarizations. Finally, the proposed antenna is suitable for base station applications.

This paper presents a CPW-fed dual-band dual-sense circularly polarized square slot antenna (CPSSA). The antenna consists of a rectangular radiator with two unequal rectangular strips, connected by a CPW feed line. An inverted L-shaped grounded stub is placed in the right side of the slotted ground plane with the orthogonal direction of the feed line to create CP modes. The proposed antenna obtained two CP bandwidths of 3.30-3.78 GHz and 5.40-5.86 GHz with axial ratio (AR) value less than 3 dB, and both the CP bands are overlapped by impedance bandwidth (IBW) of the antenna, ranging from 2.72 to 7.34 GHz. Total size of the proposed antenna is 50×50×1.58 mm³. The antenna is fabricated on an FR4-epoxy substrate and measured. Simulation results are verified by measurement for the given antenna. The designed antenna is well used for WiMAX (3.5 GHz and 5.5 GHz) band with CP characteristics. Design procedures of the antenna are discussed in details for further understanding of the antenna design. Parametric study has been done for describing the mechanism of the dual-band CP with the analysis of electric current distribution of the antenna. Meanwhile, wide axial ratio bandwidth has been obtained in both the bands using this structure compared to other published structures.

Compared with a standard permanent magnet synchronous motor, a line-start permanent magnet synchronous motor (LSPMSM) has additional features that include two-sided slots on its stator and rotor. Thus, due to its complex air gap form, there is no simple method to calculate the cogging torque of this kind of motor at present. This paper presents a new analytical method that models the rotor as an equivalent magnetic motive force (MMF) distribution in the air gap which avoids the influence of rotor slotting in the air gap. Based on the energy method, an analytical method is presented here to analyze the pole-slot match of stator and the influence of number of slots per pole of rotor on the cogging torque. The effect of auxiliary slots on cogging torque of LSPMSM is studied and by changing the number of auxiliary slots to reduce the cogging torque, the correctness of the above method has been validated by the finite element method.

A novel and systematic method is developed to evaluate periodic Green's functions on empty lattices through extractions of an imaginary wavenumber component of the lattice Green's function and its associated derivatives. We consider cases of volumetric periodicity where the dimensionality of the periodicity has the same dimensionality as the physical problem. This includes one-dimensional (1D) problem with 1D periodicity, two-dimensional (2D) problem with 2D periodicity, and three-dimensional (3D) problem with 3D periodicity, respectively. The remainder of the Green's function is put in spectral series with high-order power-law convergence rates, while the extracted imaginary wavenumber parts are put in spatial series with super-fast and close-to exponential convergence rate. The formulation is free of transcendental functions and thus simple in implementation. It is especially efficient for broadband evaluations of the Green's function as the spatial series are defined on fixed wavenumbers that take small CPU to compute, and the spectral series have simple and separable wavenumber dependences. Keeping only a few terms in both the spatial and spectral series, results of the lattice Green's function are in good agreement with benchmark solutions in 1D, 2D, and 3D, respectively, demonstrating the high accuracy and computational efficiency of the proposed method. The proposed method can be readily generalized to deal with Green's functions including arbitrary periodic scatterers.

A composite right/left-handed (CRLH) half mode substrate integrated waveguide (HMSIW) based leaky wave antenna (LWA) is designed and analyzed in this paper. Equivalent circuit of the unit cell is extracted, and the CRLH performance is clarified. Two HMSIW structures are placed back-to-back to obtain low cross-polarization performance, which is further validated by differential excitation principle. The presented LWA is demonstrated to be a balanced structure with a beam scanning range from -60° to +31°. Besides, less than 1.7 dBi gain variation in the working band (46% centered at 13 GHz) is obtained. Simulated and measured results agree well as experiment shows.

Major challenges faced by airborne VHF monopole antennas are to achieve wideband characteristics in permissible antenna height and to find the apt location for mounting, so as to satisfy sufficient ground plane around its feed point. The increased applications of electromagnetic spectrum result in a large number of antennas competing in the limited space available on platform. The asymmetries and curved surfaces on the platform as well as the limited size of the available ground plane may result in an insufficient ground plane for these antennas on platform. The deficient ground plane can deteriorate the radiation characteristics of antenna. Printed monopole antenna, which does not require a backing ground plane, can overcome this deficiency, as the ground planes of these antennas are implemented in the same plane as that of the radiating element. This paper proposes a wideband printed monopole VHF antenna for airborne applications, which simultaneously achieves reduced height and reduced ground plane on platform. The antenna has a size of 0.1045λ × 0.1272λ × 0.072λ, where λ is the free space wavelength at lowest frequency of operation, and it achieves a 3:1 VSWR bandwidth of 38%. The radiation characteristics and size of the proposed antenna are comparable to the conventional airborne blade monopole antenna with the added advantage of requiring minimal ground plane to mount on.

In this study, we propose a broad-side coupled transformer with reduced capacitance for RF CMOS power amplifier applications. The width of the secondary winding is decreased to reduce parasitic coupling capacitance. Additionally, an auxiliary primary winding is added to improve the coupling between the primary and secondary windings. To prove feasibility of the proposed transformer, we design the transformer using 180-nm RF CMOS technology. From the simulated results of a typical transformer and the proposed broad-side coupled transformer, we successfully find that the parasitic coupling capacitance of the proposed structure is reduced compared to that of a typical structure. Additionally, the auxiliary primary winding increases the maximum available gain of the proposed transformer.

This paper portrays a compact planar ultra-wideband (UWB) antenna design and development for wireless applications. The proposed antenna is influenced by fractal geometry design, where a pentagon slot is introduced inside a circular metallic patch, and iterations were carried out to achieve needed wide bandwidth. The antenna is deployed over an FR4 substrate with relative permittivity of 4.4 and thickness of 0.16 cm, to achieve wider impedance bandwidth. The proposed antenna is of low profile with dimensions of 32 mm x 32 mm, and it operates over bandwidth of 12.1 GHz (2.9-15 GHz). Specific Absorption Rate (SAR), the measure of exposure of electromagnetic (EM) energy on human tissues, is observed when proposed antenna is placed in close proximity to the dispersive phantom model. Also, the time domain analysis is done on human tissue model to observe the performance of the antenna and to validate its capability with wireless devices which are in near vicinity to the human all the time. Further, in this research, the temperature variation on human tissue is examined using Infrared (IR) thermal camera. Investigation on these parameters and validation with Radio Frequency (RF) equipment helps to prove that the proposed antenna is a suitable candidate for UWB wireless communication applications.

In this paper, we theoretically investigate the electromagnetic response of the widely used layered stacked structure. For a causality and lossy system, For a causality and lossy system, relationships between maximum values of reflection and transmission coefficients are demonstrated, which are related with many parameters, such as absolute bandwidth, layers thicknesses and real parts of the static permittivity and static permeability. Different polarizations and incident conditions are discussed. The results can provide a criterion to judge different designs operating at different spectrum ranges with different thicknesses and materials by comparing them with achievable physical limits.

Having the imaging ability of the area in front of flight direction, forward-looking synthetic aperture radar (SAR) has become a hot topic in areas of SAR research. Nevertheless, constrained by limited azimuth aperture length,the imaging of forward-looking SAR suffers from poor azimuth resolution. Aiming at this problem, an enhanced forward-looking SAR imaging algorithm is proposed in this paper. This algorithm takes both super-resolving ability and computational burden into account. Firstly, an imaging framework is proposed to decrease the computational burden. Secondly, an iterative regularization implementation of compressive sensing (CS) is proposed to improve azimuth resolution. Finally, imaging experiments based on simulated data and Ku-band complex valued image data from the MiniSAR system demonstrate the effectiveness of the proposed algorithm.

We summarize the size parameter range of the applicability of four lightscattering computational methods for nonspheric dielectric particles. These methods include two exact methods - the extended boundary condition method (EBCM) and the invariant imbedding T-matrix method (II-TM) and two approximate approaches - the physical-geometric optics method (PGOM) and the improved geometric optics method (IGOM). For spheroids, the single-scattering properties computed by EBCM and II-TM agree for size parameters up to 150, and the comparison gives us confidence in using IITM as a benchmark for size parameters up to 150 for other geometries (e.g., hexagonal columns) because the applicability of II-TM with respect to particle shape is generic, as demonstrated in our previous studies involving a complex aggregate. This study demonstrates the convergence of the exact II-TM and approximate PGOM solutions for the complete set of single-scattering properties of a nonspherical shape other than spheroids and circular cylinders with particle sizes of ~48λ, specifically a hexagonal column with a size parameter of length as kL=300, where k=2π/λ and L is the column length. IGOM is also quite accurate except near the exact 180º backscattering direction. This study demonstrates that a synergetic combination of the numerically-exact II-TM and the approximate PGOM can seamlessly cover the entire size parameter range of practical interest. To demonstrate the applicability of the approach, we compute the optical properties of dust particles with a downstream application to the retrieval of dust aerosol optical thickness and effective particle size from polarimetric observations.