In order to improve measurement efficiency in electromagnetic test facilities (compact range or near-field range), testing probes are required to have ultra-wideband (UWB) radiation characteristics, dual-polarization capability, and interchangeable E- and H-plane far-field patterns. In this context, we propose a new type of UWB antenna that satisfies these requirements in the frequency range of 4 to 18 GHz. For the proposed antenna, a low-loss dielectric material is loaded over pairs of balanced feeds to overcome radiation performance degradation addressed in purely metallic antennas. Also, radiation patterns are further improved by employing a lens aperture and shielding structures. The measured results of the final antenna design demonstrate broad and stable far-field patterns (half-power beamwidth > 45◦), low voltage standing-wave ratio (< 2), similar E- and H-plane patterns, and large cross-polarization isolation (> 23 dB).
The programmable graphics processing unit (GPU) is employed to accelerate the unconditionally stable Crank-Nicolson finite-difference time-domain (CN-FDTD) method for the analysis of microwave circuits. In order to efficiently solve the linear system from the CN-FDTD method at each time step, both the sparse matrix vector product (SMVP) and the arithmetic operations on vectors in the bi-conjugate gradient stabilized (Bi-CGSTAB) algorithm are performed with multiple processors of the GPU. Therefore, the GPU based BI-CGSTAB algorithm can significantly speed up the CN-FDTD simulation due to parallel computing capability of modern GPUs. Numerical results demonstrate that this method is very effective and a speedup factor of 10 can be achieved.
We present exact three-dimensional semi-analytical expressions of the force exerted between two coaxial thick coils with rectangular cross-sections. Then, we present a semi-analytical formulation of their mutual inductance. For this purpose, we have to calculate six and seven integrations for calculating the force and the mutual inductance respectively. After mathematical manipulations, we can obtain semi-analytical formulations based on only two integrations. It is to be noted that such integrals can be evaluated numerically as they are smooth and derivable. Then, we compare our results with the filament and the finite element methods. All the results are in excellent agreement.
A model for two-dimensional layered medium is proposed for through-wall imaging problem. It is integrated with the subspace-based optimization method for reconstructing the relative permittivity profile in a fast and robust manner. Numerical results have shown that the concealed targets within walls can be reconstructed well using the proposed model even though full aperture of targets is not available due to the presence of walls. The model has also been employed for studying the effect of the presence of walls on imaging.
This paper studies optical solitons, in presence of higher order dispersion terms by the aid of He's semi-inverse variational principle. Both Kerr law and power law are taken into consideration. The numerical simulations are also given to complete the analysis.
Up to now, the terahertz (THz) band is still an unexplored region in the sense that no practical application exists. New operating principles by traveling wave concept should be, therefore, appreciated for the real applications. In this paper, the generalized three-dimensional (3D) transverse magnetic (TM) mode analysis to analyze the characteristics of two-dimensional electron gas (2DEG) drifting plasma at the III-V high-electron-mobility-transistor (HEMT) hetero-interface such as AlGaAs/GaAs hetero-interface and its interaction with propagating electromagnetic space harmonic wave is presented. It includes, (1) the determination of electromagnetic fields in semiconductor drifting plasma using the combination of well-known Maxwell's equations and carrier kinetic equation based on semiconductor fluid model and the derivation of the effective permittivity of drifting plasma in 2DEG on semi-insulating substrate, and (2) the analysis to describe the presence of interactions using a so-called interdigital-gated HEMT plasma wave devices. To describe the interaction, the admittance of the interdigital gate is evaluated. The numerical procedures to solve the integral equations which are used in determining the admittance is explained. A negative conductance is obtained when drifting carrier velocity is slightly exceed the fundamental wave velocity indicates the significant condition of the interaction. A brief analysis and discussion on the Dyakonov-Shur THz surface wave in 2DEG is also presented.
Wide-band hybrid amplifier is theoretically proposed using a series configuration of Thulium-doped fiber amplifier (TDFA) and fiber Raman amplifier (FRA), which using the similar type of pump laser. The operating wavelength of this amplifier covers the bandwidth of entire short wavelength band (S-band) region by combining the gain spectrum of TDFA and FRA. The theoretical gain varies from 20 to 24 dB within a wavelength region from 1460 to 1525 nm and which is in a good agreement with the experimental result. The development of reliable high-power diode lasers in the 1420 nm wavelength range will make this type of wide-band hybrid amplifier an interesting candidate for S-band optical telecommunication systems.
This paper investigates the properties of the on-wafer coupled interconnects built in a 0.18 μm CMOS technology for RF applications. A SPICE compatible equivalent circuit model is developed. The proposed model is an extension of a 2-Ⅱ equivalent circuit model for single-line interconnects by adding two coupling components. The model parameters are extracted from four-port S-parameter simulation results through a calibrated electromagnetic (EM) simulator, i.e. HFSS. The accuracy of the model is validated from 500 MHz to 20 GHz.
An effective approach to characterize frequency-dispersive sheet materials over a wide RF and microwave frequency range based on planar transmission line geometries and a genetic algorithm is proposed. S-parameters of a planar transmission line structure with a sheet material under test as a substrate of this line are measured using a vector network analyzer (VNA). The measured S-parameters are then converted to ABCD matrix parameters. With the assumption of TEM/quasi-TEM wave propagation on the measured line, as well as reciprocity and symmetry of the network, the complex propagation constant can be found, and the corresponding phase constant and attenuation constant can be retrieved. Attenuation constant includes both dielectric loss and conductor loss terms. At the same time, phase term, dielectric loss and conductor loss can be calculated for a known transmission line geometry using corresponding closed-form analytical or empirical formulas. These formulas are used to construct the objective functions for approximating phase constants, conductor loss and dielectric loss in an optimization procedure based on a genetic algorithm (GA). The frequency-dependent dielectric properties of the substrate material under test are represented as one or a few terms following the Debye dispersion law. The parameters of the Debye dispersion law are extracted using the GA by minimizing the discrepancies between the measured and the corresponding approximated loss and phase terms. The extracted data is verified by substituting these data in full-wave numerical modeling of structures containing these materials and comparing the simulated results with experimental.
In the paper the unified design procedure for planar dipoles oriented on UWB application is proposed. The procedure leads to obtain a good matching characteristic of planar dipoles in UWB frequency band. The design process is split into two parts: the radiator and the balun design. The Radiator Quality Factor (RQF) is defined as an evaluation suitability of planar radiators to be matched in UWB frequency band. Based on RQF, the optimal circular radiator is chosen, and the whole dipole antenna is designed. The general algorithm of antenna design is formulated and utilised in the planar dipole with elliptical arms project. Two antennas, with circular and elliptical arms, have been fabricated and measured in order to verify the design procedure. Both antennas are characterized by the reflection coefficient less than -10 dB from 2 GHz up to 14 GHz.
A new, approximate, uniform geometrical theory of diffraction (UTD) based ray solutions are developed for describing the high frequency electromagnetic (EM) wave radiation/coupling mechanisms for antennas on or near a junction between two different thin planar slabs on ground plane. The present solution is obtained by extending the normal incidence solution in order to treat the more general case of skew (or oblique) incidence (three-dimensional 3-D). Plane wave (for oblique or skew incidence) and spherical wave illumination are all considered in this work. Unlike most previous works, which analyze the plane wave scattering by such structures via the Wiener-Hopf (W-H) or Maliuzhinets (MZ) methods, the present development can also treat problems of the radiation by and coupling between antennas near or on finite material coatings on large metallic platforms. In addition, the present solution does not contain the complicated split functions of the W-H solutions nor the complex MZ functions. Unlike the latter methods based on approximate boundary conditions, the present solutions, which are developed via a heuristic spectral synthesis approach, recover the proper local plane wave Fresnel reflection and transmission coefficients and surface wave constants of the material slabs. There is a very good agreement, with less than ± 1 dB differences when the numerical results based on the presented UTD solution for a material junction are compared with that of the MZ solution.
This paper presents a multiband folded loop antenna for smart phone applications. The proposed antenna with a symmetric loop pattern generates four resonance modes in the design bands. The current distributions of the excited resonance modes are analyzed to confirm the mode characteristic. Using a pair of tuning elements near the feed port, the impedance bandwidth is broadened to cover GSM850/GSM900/DCS/PCS/UMTS bands. This research performed simulation by a high frequency structure simulator (HFSS) to optimally design the antenna, and a practical structure was constructed to test. The current study measured the antenna parameters including reflection coefficient, radiation characteristics, peak gain, and radiation efficiency to validate the proposed antenna.
Efficient embedded antennas are needed for future wireless structural health monitoring. The input return loss and transmission losses of a dipole, a planar inverted-F antenna (PIFA), a microstrip patch, and a loop antenna are studied at around 2.45 GHz when these antennas are embedded inside a concrete cylinder. Antenna performance is investigated in free-space, in air dried concrete and in saturated concrete with and without the presence of steel reinforcements. It is observed that the maximum transmission loss for a distance of 250 mm between antennas is around 50 dB which is acceptable for inside the bridge wireless communication between sensors.
In this work, a hybrid method which combines time domain integral equation method (TDIE) with time domain physical optics method (TDPO) is presented for the problem of TM transient scattering from two-dimensional (2-D) combinative conducting targets. The explicit solution of Marching-On-in-Time (MOT) is developed. The high accuracy and efficiency of this hybrid method are demonstrated by comparing the numerical results of this hybrid method with those obtained by TDIE. To obtain 2-D transient far scattered field, a concise algorithm about time-domain near-zone to far-zone transformation without double Fourier transform is presented for TDIE and hybrid method, and its numerical results are verified by comparing with results obtained from inverse discrete Fourier transform (IDFT) techniques.
In this paper, the problem of designing linear antenna arrays for specific radiation properties is dealt with. The design problem is modeled as a single optimization problem. The objectives of this work are to minimize the maximum side lobe level (SLL) and perform null steering for isotropic linear antenna arrays by controlling different parameters of the array elements (position, amplitude, and phase). The optimization is performed using two techniques: Taguchi's optimization method and the self-adaptive differential evolution (SADE) technique. The advantage of Taguchi's optimization technique is the ability of solving problems with a high degree of complexity using a small number of experiments in the optimization process. Taguchi's method is easy to implement and converges to the desired goal quickly in comparison with gradient-based methods and particle swarm optimization (PSO). Results obtained using Taguchi's method are in very good agreement with those obtained using the SADE technique.
The problem of determining the eigenmodes of a rectangular waveguide with one hard wall formed by longitudinal corrugations with grooves filled with dielectric is considered. The characteristic equation is derived by using the asymptotic boundary conditions for corrugated surfaces. It is shown analytically that if the groove depth is equal to the value 0.25λ/(ε-1)1/2 corresponding to the hard wall condition, the TE eigenmode spectrum of the waveguide contains an infinite set of new non-uniform quasi-TEM modes with different transverse propagation constants in the empty part and identical longitudinal propagation constants equal to the wavenumber k. Analytical solution for the case of excitation of the waveguide by a specified source is given, and an example of forming local quasi-TEM waves is considered and discussed.
Microwave hyperthermia is a non-invasive treatment for cancer which exploits a selective heating of tissues induced through focused electromagnetic fields. In order to improve the treatment's efficiency, while minimizing side effects, it is necessary to achieve a constrained focusing of the field radiated by the sources. To address this issue, in this paper we present an innovative and computationally effective approach to the field focusing for hyperthermia. The proposed method, after establishing the number of sources to be used, determines the excitations of the given set of sources such to produce a maximum field in a given region of space subject to a completely arbitrary mask for the field amplitude in all other regions. As the approach relies on a formulation of the problem in terms of convex programming, it is able to achieve the globally optimal solution without the adoption of computationally intensive global optimization procedures. A preliminary assessment of the feasibility is given on hyperthermia therapy of breast cancer by means of numerical examples run on realistic 2D phantoms of female breast.
In this paper, a folded stepped impedance resonator (SIR), modified by adding an inner quasi-lumped SIR stub, is used as a basis block for a new implementation of dual-band bandpass filters. The main advantage of the proposed filter is to make it possible to independently control the electrical features of the first and second bands. The behavior of the first band basically depends on the geometry of the outer folded SIR. The second band, however, is strongly influenced by the presence of the inner stub. Additional design flexibility is achieved by allowing the inner stub to be located at an arbitrary position along the high impedance line section of the main SIR. The position of the tapped input and output lines can be optimized in order to reach a reasonable matching of the filter at the central frequencies of both passbands. Some designs are reported to illustrate the possibilities of the proposed structure. Experimental verification has been included.
A novel compact resonator for LPF is proposed in this paper. It is composed of a circular hairpin resonator and a pair of coupled parallel stepped impedance resonators (SIRs) inside. With the loaded SIRs, additional two transmission zeros can be introduced and adjusted easily to cancel the spurious responses for stopband extending, while do not change the filter size. Filters using one and two of the new cells were designed and measured. The two-cell LPF has an insertion loss less than 0.6 dB from DC to 1.6 GHz, including attenuation of double SMA transitions at both sides of the circuit which is about 0.3 dB, and a wide -10 dB stopband from 2.5 to 13 GHz (corresponding to 146% normalized 10 dB stopband), but has a size of only 0.129 λg × 0.073 λg.
Comparing with an all-dielectric binary photonic crystal, we show, in this work, that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged. First, the band gap enlargement due to the addition of the metallic film is examined in the case of normal incidence. Next, in the oblique incidence, a wider omnidirectional band gap can be obtained in such a ternary metal-dielectric photonic crystal. All the theoretical analyses are made based on the transfer matrix method together with the Drude model of metals.
Novel time-harmonic beam fields have been recently obtained by utilizing a non-orthogonal coordinate system which is a priori matched to the field's planar linearly-phased Gaussian aperture distribution. These waveobjects were termed tilted Gaussian beams. The present investigation is concerned with parameterization of these time-harmonic tilted Gaussian beams and of the wave phenomena associated with them. Specific types of tilted Gaussian beams that are characterized by their aperture complex curvature matrices, are parameterized in term of beam-widths, waist-locations, collimation-lengths, radii of curvature, and other features. Emphasis is placed on the difference in the parameterization between the conventional (orthogonal coordinates) beams and the tilted ones.
Location information is critical for the development of value-added location-based services, such as fraud protection, location-aware network access, person/asset tracking etc. Herein, a method for the enhancement of localization systems in terms of achieved accuracy is proposed, which can be applied to new as well as existing systems regardless the underlying localization technique. The method is based on modeling the position measurement error introduced by the localization algorithm using a polynomial approximation approach. Measurements results demonstrate the applicability of the proposed technique in enhancing accuracy in a low cost and efficient manner.
Waves arise in many physical phenomena which have applications such as describing the voltage along a transmission line and medical imaging modality of elastography. In this paper, estimating the parameters for two forms of lossy wave equations, which correspond to multi-mode and multi-dimensional waves, are tackled. By exploiting the linear prediction property of the noise-free signals, an iterative quadratic maximum likelihood (IQML) approach is devised for accurate parameter estimation. Simulation results show that the estimation performance of the proposed IQML algorithms can attain the optimal benchmark, namely, Cramer-Rao lower bound, at sufficiently high signal-to-noise ratio and/or large data size conditions.
We investigate the transmission properties of the Fibonacci quasiperiodic layered structures consisting of a pair of double positive (DPS), epsilon-negative (ENG) or/and mu-negative (MNG) materials. It is found that there exist the polarization-dependent transmission gaps which are invariant with a change of scaling and insensitive to incident angles. Analytical methods based on transfer matrices and effective medium theory have been used to explain the properties of transmission gaps of DPS-MNG, DPS-ENG, ENG-MNG Fibonacci multilayer structures.
A zero-bias dual-mode mixing antenna for wireless transponders is proposed in this paper. Designed over an Enhancement-mode Pseudomorphic HEMT (E-PHEMT), the mixer takes advantage of the device nonlinear characteristics around cold operation. Simple closed form expressions, obtained from time-varying circuit analysis, predict good conversion efficiency in two different operating modes without requiring DC bias. For validation, a lab prototype has been implemented and tested, to be finally integrated in a compact active printed antenna suitable for wireless sensor networks or other radio frequency identification (RFID) applications.