An electrically small half-loop antenna (ESHLA) embedded with Foster elements is analyzed using the characteristic mode (CM) theory. The resonant frequency and radiation characteristics of the ESHLA are mainly determined by the resonant mode (Mode 1). The characteristic currents of resonant mode (Mode 1) and non-resonant mode (higher order mode) prove the parallel resonance of the ESHLA. However, owing to the modal significance (MS) of the resonant mode varying fast with frequency, the proposed ESHLA has a narrow bandwidth. Analysis shows the MS of the resonant mode and the higher order mode are changed by tuning the Foster element, leading to a negative admittance variation slope in accordance with the non-Foster behavior. By replacing the Foster capacitor with the non-Foster network, both the characteristic currents and the MS are changed over a wide bandwidth. As a consequence, the introduced non-Foster network turns Mode 1 from the narrowband resonant mode into a continuous resonant mode with its radiation pattern kept invariant over a wide bandwidth. The proposed ESHLA with its non-Foster network is fabricated and measured. The measured 6-dB return loss bandwidth is about 12.7% (11.45-13 MHz), with its reflection coefficient curve being an envelope of those of Foster elements embedded ESHLA.
The communication `blackout' in the reentry stage of a space mission is a serious threat to the reentry vehicle. The terahertz (THz) technology is supposed to be a potential solution to the `blackout' problem in the recent decade. In the present paper, the relation between the THz waves' transmission in the reentry plasma sheath and the angle of attack (AOA) of the vehicle is investigated. A three dimensional numerical model is introduced in order to obtain the plasma parameters in the reentry plasma sheaths. The computation results show that both the electron density and the electron collision frequency vary with the AOA. As results, the transmission rates for the THz waves vary with the AOA as well. According to the analysis, microwave communication system is very likely to suffer from the `blackout' in the reentry stage. The THz scheme is an effective solution. The fluctuation of AOA may weaken the signal strength received by the onboard antenna. On the other hand, keeping the AOA in an appropriate range is helpful for strengthening the received THz signals. Also, the AOA for the best THz communication quality is obtained according to the analysis.
A novel field-line-circuit hybrid algorithm based on finite difference time domain (FDTD) method is devoted to predicting the electromagnetic responses of transmission line with multi-ports network in a shelter in this paper. The full wave FDTD method, transmission line FDTD method, and the modified nodal analysis (MNA) are combined to be compatible with the multi-level electromagnetic (EM) coupling progress of the electromagnetic interference (EMI) problem. The proposed method divides the EM couplings among the spatial EM fields, antennas, transmission line networks, and terminal circuits in some typical electronic systems into different levels with appreciate simulation techniques used. The accuracy of the hybrid method is verified by comparing the terminal transient voltage responses of transmission lines with the results obtained by PSPICE, and good agreements are achieved. Numerical calculations are further performed to show the terminal coupling voltages and currents, and the effects of incident directions and polarizations of the illuminated electromagnetic pulse (EMP) are both taken into account.
An octagonal shape monopole antenna with dual band-notched features used for ultra-wide band applications is presented. The monopole antenna has good impedance matching from 3.4 GHz to 12 GHz. The dual notched bands are achieved by using a U-shaped parasitic strip and meandered slot etched in the radiating patch. The first band notched is achieved using meandered slot to reduce the interference with WIMAX from 3.3 GHz to 3.9 GHz. The second band notched is achieved using U-shaped parasitic strip which is placed above the ground plane to eliminate the interference with WLAN from 5.2 GHz to 5.9 GHz. The proposed antenna is designed, simulated and measured. The measured result show that the antenna structure achieves (VSWR < 2) from 3.2 to 10.8 GHz. Also, the simulated radiation pattern and current distribution at different frequencies are presented. The measured and simulated results confirm that the proposed antenna is suitable for UWB applications.
In this paper, a measurement procedure allowing the characterization of active integrated antennas in terms of intermodulation distortion and compression point inside of a parallel plate cell is presented. The validity of the radiative measurement is shown and compared to the traditional guided procedure. A good agreement between the two methods shows that this approach allows the evaluation of the overall linearity behavior of arbitrary complex integrated antennas and can serve as a complementary tool when the traditional guided method cannot be applied.
In underwater wireless optical communication links, the suspended particles in the water can lead to multi-path transmission of the light, causing the temporal dispersion and attenuation of beam pulse. The scattering phase function is a key parameter to model angle scattering in the Monte Carlo simulation and can be approximated by the commonly used Henyey-Greenstein (HG) phase function, but in turbid sea water environment, the HG phase function cannot match well with the measured value of the particle phase function. In this work, instead of using the HG phase function, we make use of the Petzold's measured data value of the scattering phase function in turbid sea water. We propose a numerical solution for the computing of the scattering angle based on the measured particle phase function and present the difference of effect on temporal dispersion between the measurement and HG phase function. Numerical results show that our model is more accurate than the widely used HG model. An analytic double Gamma function is used to fit the Monte Carlo simulation results, and a good fit is found between the double Gamma function and the Monte Carlo simulations.
A regularization is integrated with Forward-Backward Time-Stepping (FBTS) method which is formulated in time-domain utilizing Finite-Difference Time-Domain (FDTD) method to solve the nonlinear and ill-posed problem arisen in the microwave inverse scattering problem. FBTS method based on a Polak-Ribiète-Polyak conjugate gradient method is easily trapped in the local minima. Thus, we extend our work with the integration of edge-preserving regularization technique due to its ability to smooth and preserve the edges containing important information for reconstructing the dielectric profiles of the targeted object. In this paper, we propose a deterministic relaxation with Mean Square Error algorithm known as DrMSE in FBTS and integrate it with the automated edge-preserving regularization technique. Numerical simulations are carried out and prove that the reconstructed results are more accurate by calculating the edge-preserving parameter automatically.
A nonlinear hybrid FDTD/FETD technique based on the parametric quadratic programming method is developed for Maxwell's equations with nonlinear media. The proposed technique allows nonconforming meshes between nonlinear FETD and linear FDTD subdomains. The coarse structured cells of FDTD are used in relatively simple structures with linear media, whereas fine unstructured elements of FETD based on the parametric quadratic programming method are used to simulate complicated structures with nonlinear media. This hybrid technique is particularly suitable for structures with small nonlinear regions in an otherwise linear medium. Numerical results demonstrate the validity of the proposed method.
A compact dual band-notched ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with uniform rejection performance is designed on an FR4 substrate (35×23×1.6 mm3). Compared with the existing UWB MIMO antennas, a second-order notched band with uniform performance for 5.15-5.825 GHz is achieved, which results from the interplay between a 1/3λ open-end slot and a 1/2λ parasitic strip. A 1/4λ open-end slot is also applied to the 3.3-3.7 GHz reject band. The two slots are connected at their open ends, that can help to get the uniform reject performance for 5.15-5.825 GHz and make the high cutoff frequency of the impedance matching band go toward the higher frequencies. Excluding the two rejected bands, a band with |S11|≤-10 dB, |S21|≤-17 dB and frequency ranged from 3.1 to 10.9 GHz is achieved, and results show that a uniform performance for 5.15-5.825 GHz is obtained.
This paper represents the force calculation in a radial passive magnetic bearing using Monte Carlo technique with general division approach (s-MC). The expression of magnetic force is obtained using magnetic surface charge density method which incurs a multidimensional integration with complicated integrand. This integration is solved using Monte Carlo technique with 1-division (1-MC) and 2-division (2-MC) approaches with a MATLAB programming. Analysis using established methods such as finite element method (FEM), semi-analytical method, and adaptive Monte Carlo (AMC) method has been carried out to support the proposed technique. Laboratory experiment has been conducted to validate the proposed method. 2-MC gives better result than 1-MC. The computation time of the proposed method is compared with the quadrature method, FEM and AMC. It is observed that the proposed method invites less computational burden than those methods as the algorithm adaptively traverses the domain for promising parts of the domain only, and all the elementary regions are not considered with equal importance.
This paper presents a finite-difference time-domain (FDTD) method of the infinite half-space with nonuniform meshes, aiming to speed up the FDTD calculation of scattering of buried objects. Two 1-D modified FDTD equations are employed to set plane wave excitation of the infinite half-space scattering problems. In order to reduce calculation time and meshes, a method with nonuniform meshes is applied. Fine grids are used for the buried objects and underground while coarse grids are applied for other regions. The 1-D modified FDTD equations with nouniform meshes are derived, and the settings of total-field/scattering-field (TF-SF) boundary are given. Finally, the proposed method is applied to calculate the transient scattering field of a buried mine. Numerical results demonstrate the validity of the method and the simulation time is significantly reduced when compared with uniform meshes FDTD.
The interference behaviors of a vector optical field with both radially and azimuthally variant states of polarization (SoP) through the Young's two-slits are theoretically studied. The optical field distribution with periodic stripes in the far field results from the interference of the vector optical field through the Young's two-slits with different initial SoP distributions. It is found that the far-field distribution can be manipulated by the incident vector optical field with the initial phase and SoP distributions. Particularly, the distribution of radially-variant SoP in the cross-section of the incident optical field provides an additional freedom to control the interference patterns of the x-component, y-component and total intensity distribution in far field. This approach provides a new method to further expand the functionality of an optical system by considering the distribution of SoP in field cross-section.
Standing wave between the feed and the reflectarray (RA) deteriorates the matching and antenna gain. A phase perturbation method is investigated to improve the matching of the antenna. The proposed method requires a change or deformation of the RA area facing the feed. A small circularly polarized reflectarray (CPRA) is used as an example. The reflectarray size is 6.25λ×6.25λ, which is corresponding to 25×25 elements. The feed is circularly polarized (CP) with aperture diameter 1.2×λ. The proposed method provides an acceptable compromise between achieving the matching and gain reduction. The field distribution on the symmetric line between the RA center and the feed is observed to show the behavior of the standing wave before and after implementing the proposed technique. The measured return loss becomes better than 10 dB, and a gain reduction is 0.2 dB. A measured maximum aperture efficiency of 55.4%, a 1-dB gain bandwidth of better than 33%, and the 1.5-dB axial ratio bandwidth of 33.2% are achieved.
In this paper, a novel technique for improving the torque characteristics of the Interior Permanent Magnet Synchronous Motor is proposed using rotor shape optimization. The main objective is to decrease the torque ripple while increasing average torque. The improvement process is performed for the maximum torque-angle operating point, and then studies are carried out for other currents and angles. Defining a multi-element grid on rotor surface regions in which each element could be either iron or air, the best practical rotor surface topology could be obtained to improve the overall torque characteristics of IPMSM. The best motor performance is achieved using practical rotor shapes obtained from a cluster of points in average torque versus torque ripple plane. Finally, for torque ripple cancellation, two or three alternate rotor configurations with optimized average torque and out of phase torque pulsation have been selected. This selection will guarantee improved average torque while mitigating torque pulsation by a significant margin. Using this method, a rotor topology obtained in which torque ripple is reduced by 80% with slightly improved average torque.
Several computer codes with varying accuracy from rigorous full-wave methods (highfidelity models) to less accurate Transmission Line (TL) approaches (low-fidelity model) have been proposed to solve EMC problems of interference between parasitic waves and wired communication systems. For solving engineering tasks, with a limited computational budget, we need to build surrogate models of high-fidelity (HF) computer codes. However, one of their main limitations is their expensive computational time. Rather than using only the computationally costly HF simulations, we apply another type of surrogate models, called Multifidelity (MF) metamodel which efficiently combines, within a Bayesian framework, high and low-fidelity (LF) evaluations to speed up the surrogate model building. The numerical results of combination of an expensive EMC simulator and a cheap TL code to solve a plane wave illumination problem, show that, compared to Kriging, a reliable Bayesian MF metamodel of equivalent or higher predictivity can be obtained within less simulation time.
The quantum radar cross section (QRCS) is a concept that gives information on the amount of returns (or scattered energy towards the detector) one can expect from a particular target when being illuminated with a small number of photons. This cross section is highly dependent on the target's geometry, as well as the illumination angle and the scattering angle from the target. The expression for the quantum radar cross section equation has been derived in the context of photon scattering. In this paper, it will be shown that an equivalent cross section expression, including the alternate form written in terms of Fourier transforms, can be derived using quantum scattering theory applied to non-relativistic, massive particles. Both single particle and multiple particle illumination are considered. Although this approach is formulated based upon massive, non-relativistic particle scattering, its equivalence to the expression based upon photon scattering provide many valuable insights of representing and interpreting these equations in the context of quantum radar. This includes an improved algorithm to simulate the QRCS response of an object illuminated with any number of photons desired.
This communication demonstrates the feasibility of rectifying microwave energy through one-wire with no earth return. In the proposed transmission system, a novel coaxial to Goubau line transition (referred thereafter as coaxial/G-line transition) was employed to transfer microwave power from TEM modes in a coaxial line to TM modes in a Goubau line. The captured signal at the receiving end of the Goubau line can be either directly used for communication or rectified into a DC. The proposed system can be used as an emergency source of power supply for cable cars, escalators and window cleaning gondolas in the event of accidents. According to our experimental results, a 0 dBm microwave signal can be transmitted through a single conductor of 13 cm in length with an insertion loss of less than 3 dB. When the input power was raised to 15 dBm, the electromagnetic energy at the receiving end can be rectified at 1.36 GHz into a DC with the efficiency at approximately 12.7%.
This article proposes a new scheme of real-coefficient fitting both Green's function and its gradient with Fast Fourier Transform (RFGG-FG-FFT) for combined field integral equation (CFIE) to compute the conducting object's electromagnetic scattering, which improves original fitting both Green's function and its gradient with Fast Fourier Transform (FGG-FG-FFT) on efficiency. Firstly, based on Moore-Penrose generalized inverse, an equivalent form of fitting matrix equation is obtained containing the property of Green's function's integral proved by addition theorem. Based on this property, with truncated Green's function new fitting technique is presented for computing fitting coefficients with real value expression, which is different from complex value expression by the original fitting technique in FGG-FG-FFT. Numerical analysis of error shows that new fitting technique has the same accuracy, but only one half of sparse matrices' storage compared to the original fitting technique in FGG-FG-FFT. Finally, the new scheme combining FGG-FG-FFT and new fitting technique is constructed. Some examples show that the new scheme is accurate and effective compared to FGG-FG-FFT and p-FFT.
In this work, the problem of mutually coupled dipole antenna array failure has been solved using bat algorithm by adjusting only the amplitude excitation of good array elements. The element failure causes the degradation of side-lobe power level to an improper level. A fitness function is formulated to obtain the difference between degraded side-lobe pattern and measured side-lobe pattern, and a flexible approach using bat algorithm is used to minimize this function. Numerical examples of single and multiple element failure correction under mutual coupling conditions are discussed to show the capability of this proposed approach.
The properties of higher order radial modes of electromagnetic azimuthal surfacetype waves (ASW) which propagate in partially plasma-filled cylindrical waveguides without external magnetic field are analyzed using analytical and numerical techniques. For a waveguide with plasma surrounded by dielectric material and encased in metal, the eigenfrequencies for higher order radial modes are obtained. It is found that the ASW higher radial modes propagate with shorter vacuum wavelength than the zero-th order radial modes and that the more favourable conditions for higher order radial mode propagation are for ASW's with larger azimuthal wavenumber in waveguides with wider dielectric layer and larger dielectric constant. A further salient feature of ASW higher radial modes is that a change in plasma waveguide parameters causes a drastic change in ASW eigenfrequency in contrast to the zero-th order modes which have a smoother frequency variation with effective wavenumber.