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.
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.
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.
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.
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.
This paper presents the pole-zero analysis of microwave filters using contour integration method exploiting right-half plane (RHP). The poles and zeros can be determined with only S21 by exploiting contour integration method on the RHP along with certain S matrix properties. The contour integration in the argument principle is evaluated numerically via the finite-difference method. To locate the poles or zeros, the contour divide and conquer approach is utilized, whereby the contour is divided into smaller sections in stages until the contour enclosing the pole or zero is sufficiently small. The procedures to determine the poles and zeros separately are described in detail with the aid of pseudocodes. To demonstrate the effectiveness of the proposed method, it is applied to determine and analyze the poles and zeros of various microwave filters.
In this paper, a simple and fast calibration algorithm is proposed for an active phased antenna array measurement of the amplitude and phase of all the antenna elements. Euler's numerical method is used to simultaneously measure and calibrate the array element's electric field and array factor. Each element's phase shifts are periodically varied with a reference state, and their variations are calculated and analyzed for signal calibration. The method is theoretically studied using numerical simulations providing accurate performance and a very low tolerance to errors. This method provides a multiple element far field calibration technique applicable to radar, satellite, and wireless communication.
Wireless power transmission (WPT) based on near-field inductive coupling is a promising solution to power a tether-less capsule robot (CR) for medical application, and it is normally implemented with a one-dimensional transmitting coil for exciting an alternating magnetic field and an three-dimensional (3-D) receiving coil onboard the CR for induction. The connection way of the 3-D receiving coil has an influence on its output power supplied to the CR, but a method for quickly selecting series/parallel connection is not available yet. This paper is dedicated to developing such a method. Firstly, an analytical expression of the output power of the 3-D receiving coil when selecting series/parallel connection was derived, and its correctness was experimentally validated: the calculated output power using the analytical expression matched well with the measured one, having an average deviation of 1.42%/0.57% when selecting series/parallel connection. Then, a criterion for quickly selecting the connection way was deduced from the analytical expression, which indicates that the connection way is much related to the CR load: when the CR load is smaller than a critical load, parallel connection enables a larger output power average; otherwise, series connection does. A calculation method of the critical load is also given, which can be determined by available parameters relating to the transmitting coil and 3-D receiving coil. Thus, this paper provides a guidance for quickly selecting the connection way of the 3-D receiving coil.
This paper presents a miniaturized dual-band antenna with a rectangular patch and symmetrically placed circles in the partial ground plane. The dimensions of the proposed antenna are 15 * 20 * 1.5 mm3, and the antenna is excited by a 50 Ω microstrip line from the bottom. The proposed antenna is fabricated on the commercially available low-cost FR4 substrate having relative permittivity εr = 4.3 and loss tangent 0.025. By introduction of a rectangular slot with a T-shape in the ground plane and a rectangular patch, the lower frequency band is achieved. The peak gain and radiation efficiency of the proposed antenna are 2 dB and 78%. The proposed antenna operates at 2.846 GHz to 3.24 GHz and 4.05 GHz to 6.22 GHz frequency range. The antenna finds its application in S-band, 5.5/5.8 GHz WiMAX bands, and 4.9/5/5.9 GHz Wi-Fi bands.
A mathematical model is constructed for calculating a three-dimensional quasistationary electromagnetic field in a piecewise-homogeneous medium containing massive conductors which is excited by a variable magnetic field. The field is varying in time according to an arbitrary law. It is proposed to use the integral relation instead of the boundary condition written at a point, which allows one to get away from the problem of collocation points and at the same time increase the computational efficiency of the numerical model. The magnetic field is calculated for the case of the excitation of eddy currents in a conducting sample containing a cut of finite size. The results obtained are confirmed by natural experiments.
In this paper, we investigate the secrecy design in a sustainable relay network, where the relay is energy harvesting enabled and utilizes time switching to harvest wireless power. Specifically, assuming half-duplex amplify-and-forward relaying, we investigate the worst-case secrecy rate maximization by jointly designing the relay beamforming matrix, artificial noise covariance, and the time switching ratio. However, the formulated problem is highly non-convex due to the secrecy rate function and the dynamic relay transmit power constraint. By decoupling the original problem, we propose a two-layer optimization algorithm, where the outer problem is solved by two-dimensional search while the inner problem is solved by semi-definite relaxation. Numerical results show the effectiveness of the proposed scheme.
In this paper a novel robust beamforming method is devised to receive multipath signals effectively. The new algorithm constructs a transformation matrix derived through high-order angle constraint to suppress the interferences with the directions of arrival (DOA) of interference signals. Using the transformed data, the composite steering vector of the multipath signals is estimated as the principal eigenvector of the signal subspace, and then it is utilized in minimum variance distortionless response (MVDR) beamforming to compute the optimal weight vector. The new method is improved in robustness to DOA error by forming wide nulls in incident directions of the interferences, and keeps effective in the presence of coherent interferences. Simulations analyses are provided to illustrate the robustness and effectiveness of the new beamformer.