A novel slot array antenna with two layers of substrate integrated waveguides (SIW) is presented for millimeter-wave wireless applications. Unlike conventional SIW-based slot arrays, in this structure a feed waveguide is placed underneath the main substrate layer containing the slot array and is coupled to the branches of the array via slanted slots. The proposed feeding structure results in a considerable reduction in size and eliminates unwanted radiations from the feed network. Experimental results for two slot arrays with 4×4 and 6×6 elements operating at 60 GHz are presented showing 14.8 dB and 18.5 dB gain, respectively. Furthermore, a novel doubly tapered transition between SIW and microstrip line is presented which is particularly useful in mm-wave applications.
Wireless Sensor Networks (WSNs) have attracted a great deal of research interest during the last few years. Potential applications make them ideal for the development of the envisioned world of ubiquitous and pervasive computing. Localization is a key aspect of such networks, since the knowledge of a sensor's location is critical in order to process information originating from this sensor, or to actuate responses to the environment, or to infer regarding an emerging situation etc. Indoor localization in the literature is based on various techniques, ranging from simple Received-Signal-Strength (RSS) to the more demanding Time-of-Arrival (ToA) or Direction-of-Arrival (DoA) of the incoming signals. In the context of several EU research projects, various WSN platforms for indoor localization have been developed, evaluated and tested within real-world emergency medical services applications. These platforms were selected in order to deal with all principal localization techniques, namely RSSI, ToA and DoA. Deployment and real-world considerations are discussed, measurements results are presented and overall system evaluation conclusions are drawn regarding indoor localization capabilities of WSNs.
A highly accurate, fast algorithm is proposed to evaluate the finite Fourier transform of both continuous and discontinues functions. As the discretization is conformal to the function discontinuities, this method is called the conformal Fourier transform (CFT) method. It is applied to computational electromagnetics to calculate the Fourier transform of induced electric current densities in a volume integral equation. The spectral discrimination in the CFT method can be arbitrary and the spectral range can be as large as needed. As no discretization for the Fourier exponential kernel is needed, the CFT method is not restricted by the Nyquist sampling theorem, thus avoiding the aliasing distortions that exist in other traditional methods. The accuracy of the CFT method is greatly improved since the method is based on high order interpolation and the closed-form Fourier transforms for polynomials partly reduce the error due to discretization. Assuming Ns and N are the numbers of sampling points in the spatial and frequency domain, respectively, the computational cost of the CFT method is O((M + 1)N log2L), where M is the interpolation order and L=(Ns−1)/M. Applications in spectral analysis of electromagnetic fields are demonstrated.
The frequency-domain finite-difference (FD-FD) methods have been successfully used to obtain numerical solutions of two-dimensional (2-D) Helmholtz equation. The standard second-order accurate FD-FD scheme is known to produce unwanted numerical spatial and temporal dispersions when the sampling is inadequate. Recently compact higher-order accurate FD-FD methods have been proposed to reduce the spatial sampling density. We present a semi-analytical solution of 2-D homogeneous Helmholtz equation by connecting overlapping square patches of local fields where each patch is expanded in a set of Fourier-Bessel (FB) series. These local FB coefficients are related to total eight points, four on the sides and four on the corners, on the square patch. The local field expansion (LFE) analysis leads to an improved, compact FD-like, nine-point stencil for the 2-D homogeneous Helmholtz equation. We show that LFE formulation possesses superior numerical properties of being low dispersive and nearly isotropic because this method of connecting local fields merely ties these overlapping EM field patches already satisfy the Helmholtz equation.
This paper presents an efficient and accurate hybrid approach of method of moments (MoM) and physical optics (PO) for radiation problems such as antennas mounted on a large platform. The new method employs higher-order hierarchical Legendre basis functions in the MoM region and higher-order Nyström scheme in the PO region. The two regions are both discretized with large domains. The unknowns can be much less than those in the small-domain MoM-PO solutions, which will lead to a great reduction in computation complexity. Furthermore, with the Nyström scheme in the PO region, the higher-order accuracy is maintained, and the calculation of the impedances can be more efficient than that in the existing higher-order MoM-PO procedure. Numerical results show the validity of the proposed method.
We present here the solution of the eigenvalue problems for the open metamaterial square and circular rod waveguides. The Maxwell's equations for the electrodynamical analsis of the open waveguides were solved by the Singular Integral Equations' (SIE) method and partial area method. Our SIE method is pretty universal and let us rigorously analyze open waveguides electrodynamically with any arbitrary cross-sections taking into account of the edge condition. The false roots did not occur applying the SIE method. The waveguide media can be of strongly lossy materials. The signs of the complex permittivity and permeability can be positive or negative in different combinations. We used our computer algorithms based on the two mentioned methods with 3D graphical visualization in the MATLAB language. We present here our numerical calculations of the metamaterial square waveguide with sides equal to 5×10-3m and the metamaterial circular waveguide with the diameter equal to 5×10-3m. We present dependences of phase constant and attenuation constant of metamaterial waveguides at the frequency range from 75 GHz till 115 GHz. We have compared the three dimension (3D) electric field distributions of the main mode and the first higher mode propagating in the square and circular metamaterial waveguides. The calculations of the electric fields were fulfilled at approximately 10000 points in every cross-section. We discovered that the electric field is concentrated at the waveguide boundary. The distribution of the electric field along the perimeter of the waveguide is not uniform. There are two areas on the perimeter of the square and circular waveguides where the electric field has maximum values. These areas are shifted relative to each other on π radians.
During the past decades there has been a tremendous increase throughout the scientific community for developing methods of understanding human brain functionality, as diagnosis and treatment of diseases and malfunctions, could be effectively developed through understanding of how the brain works. In parallel, research effort is driven on minimizing drawbacks of existing imaging techniques including potential risks from radiation and invasive attributes of the imaging methodologies. Towards that direction a new near field radiometry imaging system has been theoretically studied, developed and experimentally tested and all of the aforementioned research phases are herein presented. The system operation principle is based on the fact that human tissues emit chaotic thermal type radiation at temperatures above the absolute zero. Using a phase shifted antenna array system, spatial resolution, detection depth and sensitivity are increased. Combining previous research results, as well as new findings, the capabilities of the constructed system, as well as the possibility of using it as a complementary method for brain imaging are discussed in this paper.
Automated and accurate classification of magnetic resonance (MR) brain images is an integral component of the analysis and interpretation of neuroimaging. Many different and innovative methods have been proposed to improve upon this technology. In this study, we presented a forward neural network (FNN) based method to classify a given MR brain image as normal or abnormal. This method first employs a wavelet transform to extract features from images, and then applies the technique of principle component analysis (PCA) to reduce the dimensions of features. The reduced features are sent to an FNN, and these parameters are optimized via adaptive chaotic particle swarm optimization (ACPSO). K-fold stratified cross validation was used to enhance generalization. We applied the proposed method on 160 images (20 normal, 140 abnormal), and found that the classification accuracy is as high as 98.75% while the computation time per image is only 0.0452s.
A novel method based on the hybrid volume-surface integral equation (VSIE) and the impedance matrix interpolation technique is presented for the fast analysis of microstrip antennas in frequency sweeps. A novel impedance matrix interpolation scheme is extended to the impedance matrix associated with VSIE, thus providing high accuracy, high efficiency, and large interpolation bandwidth for metal-dielectric composite problems. To demonstrate the effectiveness and accuracy of the proposed technique, numerical results for typical rectangular patch antennas and a broadband U-slot rectangular patch antenna are presented. Good agreement among the interpolation results, the exact method of moments (MoM) solutions, the finite element method (FEM) solutions, and measured data is observed over the bandwidth. The interpolation bandwidth is further investigated through a scattering problem. Numerical results show that high accuracy is obtainable within 10:1 bandwidth.
In this paper, the synthesis of sub-arrayed monopulse planar arrays providing an optimal sum pattern and best compromise difference patterns is addressed by means of an innovative clustering approach based on the Ant Colony Optimizer. Exploiting the similarity properties of optimal and independent sum and difference excitation sets, the problem is reformulated into a combinatorial one where the definition of the sub-array configuration is obtained through the search of a path within a weighted graph. Such a weighting strategy allows one to effectively sample the solution space avoiding bias towards sub-optimal solutions. The sub-array weight coefficients are then determined in an optimal way by exploiting the convexity of the problem at hand by means of a convex programming procedure. Representative results are reported to assess the effectiveness of the weighted global optimization and its advantages over previous implementations.
In this paper, an improved TRL (Thru-Reflect-Line) calibration method is presented. This method is based on ten-term error model of a two-port vector network analyzer(VNA) measurement system. Eight error terms induced by fixtures as well as two leakage errors are derived directly from the S parameters of the calibration standards measured from the coaxial reference plane without converting S parameters to T parameters. To validate our algorithm, a microstrip device with a via hole and a coplanar waveguide transmission line are fabricated and calibrated using the present TRL calibration method and Engen's algorithm, respectively. The magnitudes and phases of S11 and S21 of the devices are compared. The consistency of the de-embedded results with those calibrated by Engen's TRL algorithm illustrates the validity of the TRL algorithm in this paper.
To simulate imaging systems, Fourier optics has been applied very successfully to optics for decades. However, when simply moving to indoor millimeter wave imaging systems, some assumptions underlying the Fourier optics may break down, which contribute to the errors by applying Fourier optics. During the review of mathematical derivation of the Fourier optics, we point out how the errors are introduced by making the Fresnel approximation and omitting the phase factors. To distinguish from much literature, we discuss the accuracy of Fresnel approximation rather than plane wave. Moreover, we check the simulation results for millimeter wave imaging systems working in both pixel scanning mode and focal plane array mode and compare them to the results predicted by Fourier optics. It is shown that the difference can be 28% for the speckle contrast when the object is with certain roughness. The optical routine is that when the lens is four times'larger than the object, the imaging system can be considered as isoplanatic, thus Fourier optics can hold. Our simulation results imply that it may not be valid in indoor millimeter wave imaging systems. The goal of this paper is to draw some attention to the possibly large errors when modeling or designing the indoor millimeter wave imaging systems by Fourier optics directly. The mathematical discussions of the inaccuracies due to some approximations in Fourier optics can serve to understand and deal with aberrations.
The earlier developed combined beam-absent analysis of the disc-loaded-coaxial waveguide in two-configurations (part-1) has shown promise for wideband gyro-traveling-wave tube (gyro-TWT) if the configurations are used as interaction structure. In the present paper, the beam-present dispersion relation and small-signal gain equation in Pierce's format for the disc-loaded-coaxial waveguide were developed. A broadening of the device bandwidth was presented by disc-loading the coaxial waveguide interaction structure of a gyro-TWT with a comparison against the circular cylindrical waveguide, coaxial waveguide, and disc-loaded circular waveguide in their respective gain-frequency responses obtained by using a numerical computer code on the basis of the present beam-present analysis.
The electromagnetic field analysis of the disc-loaded-coaxial waveguide in two configurations was developed in TE-mode for its potential application in the fast-wave regime using the field matching technique at the cylindrical interface between disc-free and disc-occupied structure regions. The space harmonics were considered for the axial periodicity and the azimuthal harmonics were ignored for azimuthal symmetry of the present configurations. The dispersion and azimuthal interaction impedance characteristics obtained by present analysis were validated against those obtained by simulation software --- HFSS within 0.1% and 0.5%, respectively. In special cases, the disc-loaded-coaxial structure reverts to well known conventional structures. The effect of structure parameters on the shape of dispersion characteristics was investigated in order to obtain a wideband-coalescence between the beam- and waveguide-mode dispersion characteristics, required for the wideband device performance, without deteriorating the impedance value.
In this paper, a three dimensional geometrical scattering channel model for indoor and outdoor wireless propagation environments is introduced. It is based on the assumption that the scatterers are distributed within a spheroid, in which the mobile station and base station are located at the spheroid's foci. This model captures both the spatial and temporal statistical distributions of the received multipath signals. Several angle of arrival and time of arrival probability density functions of the received multipath signals are provided in compact forms. The angle of arrival probability density functions are obtained in terms of both the azimuth and elevation angles. Numerical results are presented to illustrate and verify the derived expressions. To validate the model, it has been compared against some available two dimensional models and measured data.
Here we present the rigorous electrodynamical solution of microwave scattering by a multilayered electrically or (and) magnetically anisotropic circular cylinder. The number and thickness of layers may be arbitrary. We present the solution when all area of multilayered cylinder can be made of different uniaxial anisotropic or isotropic materials. The multilayered cylinder media can be of strongly lossy materials. The signs of the complex permittivity and permeability tensor components can be positive or negative in different combinations. Here we present the numerical dependencies of the Poynting vector radial component Pρ that is responsible for the scattered and absorbed powers when the incident microwave impinges on the anisotropic Lithium Niobate (LiNbO3) cylinder as well as on two single isotropic cylinders. The permittivity tensor components of the anisotropic cylinder are εt=43-i0.0005, εp=28-i0005 as well as for the isotropic cylinders the permittivities are εt=εp=43-i0.0005 and εt=εp=28-i0.0005. We show here the pattern of the value Pρ inside and outside of the LiNbO3 and two isotropic cylinders when the polar angle changes from 0 to 360 degrees with the step equal to one degree. We present here our calculations when the incident microwave has perpendicular or parallel polarization at three frequencies 65 GHz, 92.5 GHz and 120 GHz. We found that the values Pρ for the anisotropic cylinder have the opposite behavior of dependencies on the permittivity tensor components for the incident microwaves of different polarizations.
Integration of multiple functions is for the first time achieved within a single patch element. Firstly, out of phase equal power division and bandpass filter characteristics are combined within a patch element. The novelty of the proposed structure is to use simple asymmetric cross slots in the patch element to achieve this integration. A simplified equivalent circuit model to describe operation of this patch element is proposed. Coplanar waveguide/microstrip broadside coupling is then investigated to enhance the performance of the patch balanced filter and eliminate narrow coupling gaps and microstrip lines. Subsequently, transition between microstrip and coplanar waveguide is then added to the patch element by using certain electromagnetic coupling methods for higher level integration without introducing additional loss. Different patch elements operating at 2.4 GHz are developed to validate the feasibility of the proposed structures. The circuits were designed, fabricated and measured. The measured results agree quite well with the simulation, exhibiting small amplitude and phase imbalance at the output ports throughout the desired passband, and good rejection levels elsewhere.
In this paper, a new technique is developed to evaluate efficiently the Sommerfeld integrals arising from the problem of a current element radiating over a lossy half-space. The annihilation of the asymptote and the branch-point singular behavior of the spectral Green's function is used in this technique. The contributions of the subtracted asymptotic and singularity terms are calculated analytically. The annihilation results in a remaining integral that is very smooth and can be calculated adaptively by using Gaussian quadratures and extrapolation methods to accelerate the convergence of the oscillating integrand. The accuracy and efficiency of the new technique has been confirmed by comparison with literature, and the commercial software NEC. The application of the proposed technique provides a robust and rapid procedure to calculate spatial Green's functions which can be used in ground-wave propagation, and lightning return stroke channel modeling.
In this paper we present a new method for the design of multi-band microstrip filters. The proposed design method is based on Differential Evolution (DE) with strategy adaptation. This self-adaptive DE (SaDE) uses previous experience in both trial vector generation strategies and control parameter tuning. We apply this algorithm to two design cases of dual and tri-band filters for WiFi and WiMax applications. We select the Open Loop Ring Resonator (OLRR) filters, which are comprised of two uniform microstrip lines and pairs of open loops between them. The results indicate the advantages of this approach and the applicability of this design method.
A non-resonant microwave method has been proposed for accurate and stable constitutive parameter measurement of low-loss dispersive and non-dispersive isotropic materials. The method uses transmission-only measurements of two configurations: a) the sample inside a sample holder and b) the sample backed by a reference sample inside the same holder. It is not prone to undesired ripples in the extracted constitutive parameters arising from measured similar reflection properties. In addition, its accuracy is higher since it is not much affected by surface roughness and/or unevenness of the sample or the reference sample. It is based on frequency-by-frequency extraction and thus suitable for dispersive materials. However, it requires the selection of an appropriate reference sample. The method has been validated by measurements at Xband (8.2--12.4 GHz) of a low-loss sample located into a waveguide sample holder.
Apertureless scanning near-field optical microscopy (A-SNOM) with a superlens is a novel nano-optical system for sub-wavelength imaging purposes. This study presents a quantitative model for analyzing the heterodyne signals obtained from an A-SNOM fitted with a superlens at various harmonics of the AFM tip vibration frequency. It is shown that the image resolution is determined not only by the tip radius, but also by the superlens transmission coefficient in the high evanescent wave vector Kx. Moreover, the analytical results show that the images acquired from the A-SNOM/superlens system are adversely affected by a signal contrast problem as a result of the noise generated by the tip-superlens interaction electric field. However, it is shown that this problem can be easily resolved using a background noise compensation method, thereby resulting in a significant improvement in the signal-to-background (S/B) ratio. The feasibility of utilizing the system for maskless nanolithography applications is discussed. It is shown that the A-SNOM/superlens system with the proposed noise compensation scheme yields a dramatic improvement in the signal intensity and S/B ratio compared to that of a conventional A-SNOM with a bare tip only.
Synthetic Aperture Radar (SAR) can obtain a two-dimensional image of the observed scene. However, the resolution of conventional SAR imaging algorithm based on Matched Filter (MF) theory is limited by the transmitted signal bandwidth and the antenna length. Compressed sensing (CS) is a new approach of sparse signals recovered beyond the Nyquist sampling constraints. In this paper, a high resolution imaging method is presented for SAR sparse targets reconstruction based on CS theory. It shows that the image of sparse targets can be reconstructed by solving a convex optimization problem based on L1 norm minimization with only a small number of SAR echo samples. This indicates the sample size of SAR echo can be considerably reduced by CS method. Super-resolution property and point-localization ability are demonstrated using simulated data. Numerical results show the presented CS method outperforms the conventional SAR algorithm based on MF even though small sample size of SAR echo is used in this method.
The reliability of circuits on printed circuit boards (PCBs) in many modern electronic products is affected by severe noise caused by high-speed and low-voltage operation as well as layout constraints compounded by limited space and high circuit density. Crosstalk is a major noise source that interferes with the signal integrity (SI) in poor PCB layout designs. One common method of reducing crosstalk is the three-width (3-W) rule. The serpentine guard trace (SGT) approach has also been used to reduce crosstalk using two terminal matching resistors on the SGT between the aggressor and victim. Although the SGT approach suppresses far-end crosstalk (FEXT) at the expense of more layout space, it also neglects interference caused by near-end crosstalk (NEXT). In this study, we propose the SGT via (SGTV) approach in which grounded vias are added to the SGT at appropriate locations, and the ratio between the lengths of the horizontal and vertical sections of the guard trace is adjusted to minimize NEXT and FEXT. Frequency domain simulated (measured) results showed that the SGTV approach reduced NEXT by 3.7 (7.65) and 0.83 (1.6) dB as well as FEXT by 5.11 (7.22) and 0.1 (1.98) dB compared to the 3-W and SGT approaches, respectively. In the time domain, simulated (measured) results showed that SGTV reduced NEXT by 34.67% (49.8%) and 27.5% (26.65%) as well as FEXT by 46.78% (56.52%) and 6.91% (24.8%) compared to the 3-W and SGT approaches, respectively. Our proposed approach thus effectively suppresses both NEXT and FEXT to achieve better SI in PCB layout designs than the other two methods. As our design uses two grounded vias instead of two guard trace terminators and does not require extra components, it is less costly than SGT. Our simulated and measured results indicate that our approach is suitable for practical application because of the lower cost and the ease of implementation that eliminates NEXT and FEXT.
Scattering of electromagnetic radiation by a charged homogeneous spherical particle/body is treated. Theoretical solution represents a generalization of the Mie's scattering theory for electrically neutral sphere. It is shown that classical and quantum physics approaches may lead to different conclusions, as documented by numerical computations assuming various permeabilities, refractive indices, surface charges, temperatures, and other physical parameters of the spherical particles. Two discrete wavelengths (5 μm and 1mm) of the incident radiation are considered. Optical properties of charged particles composed of absorbing and slightly absorbing materials can essentially differ. Especially, the resonance peaks typically occur when imaginary part of particle refractive index is low. The relative permeability of a material may differ from unity at large wavelengths, e.g., in microwave region. Basically, the relative permeability appears to be less important factor than the surface charge. However, the permeability can influence the scattering and extinction efficiencies, as well as the backscattering features of small particles, under some conditions.
A compact multiband (GSM/DCS/PCS/UMTS/Bluetooth/WLANs/ Wi-MAX) planar monopole antenna, which contains multiple branches, is proposed in this work. Most wireless communication bands for consumer electronics are covered in this design. The antenna radiator comprises four resonant branches on the top surface of a PCB board and one parasitic element on its back. The antenna size is 17.5 mm×35.7 mm, and no via is needed in the fabrication process. Various techniques, such as branching, meandered lines, closed loop, capacitive coupling, parasitic elements and tapered ends, are used to enhance the antenna's bandwidth, matching and size reduction performance. Simulation and measurement show good agreement for reflection coefficient. The proposed antenna is particularly attractive for mobile devices that integrate multiple systems.