The present paper is a study of adaptive beamforming (ABF) techniques applied to antenna arrays. The structure of these techniques is based on Taguchi's Optimization (TagO) method. The high convergence speed and the ability to reach near-optimal solutions by adjusting only one parameter make the Taguchi's method an attractive choice for real time implementations like the case of ABF. Modifications are proposed in order to enhance the applicability of the TagO algorithm and decrease the computational time needed by the algorithm to terminate. The TagO method is used here to construct an ABF technique that aims at steering the main lobe of a uniform linear array towards a signal of interest, under the constraint of low side lobe level (SLL) or the constraint of placing radiation pattern nulls towards respective interference signals. Properly defined fitness functions must be minimized by the TagO algorithm to satisfy respectively the above mentioned constraints. The TagO-based ABF technique is compared with typical beamforming methods, like the Sample Matrix Inversion (SMI) and Maximum Likelihood (ML) ones, and with two evolutionary ABF techniques based on Particle Swarm Optimization (PSO) and Differential Evolution (DE), respectively. The comparison is performed regarding the convergence speed, the ability to achieve better fitness values in less time, the ability to properly steer the main lobe and finally the null-steering ability or the SLL control depending on the constraint type. The results exhibit the superiority of the TagO-based technique.
The one-port cavity resonator method based on the S11 parameter measurement technique for measuring the complex permittivity of dielectric samples has been proposed. A novel dual-loop coupler is developed for avoiding and suppressing the spurious modes in one-port cavity resonator. Through threading the pair of half loop in the opposite direction, the opposite surface currents can be generated and only TE011 mode will be excited. The operating principles of the dual-loop coupler are investigated. This technique has the advantages of the coupling. Equivalent electronic circuit model has been set up. Simulation and experimental results show good agreement.
A novel planar ultra-wideband (UWB) antenna with dual band-notched characteristics is proposed. The antenna is fabricated on a printed circuit board (PCB), having a circular monopole and arc-shaped parasitic strips on one side and a ground plane with a slot aperture on the other side. Two narrow bands at 5.15-5.35 GHz and 5.725-5.825 GHz are notched by using two arc-shaped parasitic strips on the same layer of the radiator. Compared with other band-notched UWB antennas, the proposed antenna exhibits the advantages of simple structure, compact size, simple control of each notched frequency band using separate parasitic strips, and good performance. Surface current distributions and equivalent circuit model are applied to analyze the operating principle of the proposed antenna. To validate the concept, a prototype is fabricated and tested. Both simulated and measured results confirm that the proposed antenna achieves a wide bandwidth from 3.1 GHz to 10.6 GHz with two narrow bands notched successfully. The results of VSWR, radiation patterns and gain response are shown and discussed in detail. The antenna enables the independent control of the notched frequency bands, and the proposed method can be extended for designing planar UWB antennas with multiple band-notched characteristics and reconfigurable notched frequency.
In this investigation, scattering from a circular disk with surface impedance has been studied rigorously. The method of analysis is Kobayashi Potential (KP). The mathematical formulation yields the dual integral equations (DIEs). These DIEs are solved by using the discontinuous properties of Weber-Schafheitlin's integral. After applying the boundary conditions and projection, the resulting expressions, finally, reduce to matrix equations for expansion coefficients. The matrix elements are in the form of infinite integrals with single variable. These are then used to compute the values of expansion coefficients. The far field patterns of the scattered wave are computed for different incident angles and surface impedances for both E- and H-polarizations. To verify the results, we have computed the solution based on the physical optics approximation. The agreement between them is fairly good.
In this work, an electronically tunable large range phase shifter based on a broadband Injection-Locked Third Harmonic Self-Oscillating Mixer (IL3HSOM) is designed and analyzed. This multifunctional circuit generates a down-converted Intermediate Frequency (IF) signal and provides a theoretical 540◦ continuous phase shift range. The conversion gain and the bandwidth of the circuit are optimized through bifurcation control techniques. The IL3HSOM will be used as the core of a broadband phased antenna array with electronic beam-steering capabilities. The use of a multi-harmonic load based on an arbitrarily width modulated transmission line allows the nonlinear optimization of the circuit phase shift frequency response to ompensate the frequency scanning effect, which negatively influences the performance of broadband antenna arrays.
Principle component analysis based through wall image enhancement is proposed which is capable of discriminating target, noise and clutter signals. The overlapping boundaries of clutter, noise and target signals are separated using fuzzy logic. Fuzzy inference engine is used to assign weights to principle components. The proposed scheme works well significantly for extracting multiple targets having different range profiles in heavy cluttered through wall images. Simulation results are compared on the basis of mean square error, peak signal to noise ratio and visual inspection.
The research about the so-called \emph{complex beams}, localized solutions of the Helmholtz wave equation, lead to the problem of finding the sources of such solutions, which may be formally expressed as a Dirac delta function of a complex argument. To investigate about the meaning of the Dirac delta distribution of complex argument, the Green's function of the 3D Poisson problem with a point source localized at an imaginary position in free space is considered. The main physical features of the potential created by that source are described. The inverse problem consists in looking for the real source distribution which causes that potential. The sources appear on a disk in the real space. Their physical interpretation requires a regularization process based on including the border of the disk.
This investigation is one of the first steps towards the realization of low-cost, mass producible, miniaturized antenna solutions utilizing screen printed magnetic thick films of cobalt nanoparticle ink. The ink has a curing temperature lower than 125°C, feasible printing characteristics and metal loading higher than 85 wt.%. The properties are achieved by using an oxidatively polymerising natural fatty acid, linoleic acid, both as a surfactant and a binder. DSC-TGA-MS-analysis, TEM and SEM microscopies were utilized to investigate ink composition, nanoparticle coating and print quality. The resonant frequency of a microstrip patch antenna was tuned by screen printing of cobalt nanoparticle ink with different layer thicknesses on top of the antenna element. The influence of magnetic layers on resonance frequency, return loss, total efficiency and radiation pattern was measured and compared with a reference antenna without the magnetic films. For example, five layers of magnetic film (52 μm total thickness) tuned the resonance frequency (2.49 GHz) of the patch antenna by 68 MHz. The radiation efficiency of the patch antenna was increased from 39% to 43% by the loading of a 52 μm thick magnetic film compared to the reference antenna. The radiation patterns remained essentially unchanged, despite the presence of the magnetic thick films.
The time-domain studies of the modal fields in a lossy waveguide are executed. The waveguide has a perfectly conducting surface. Its cross section domain is bounded by a singly-connected contour of rather arbitrary but enough smooth form. Possible waveguide losses are modeled by a conductive medium which fills the waveguide volume. Standard formulation of the boundary-value problem for the system of Maxwell's equations with time derivative is given and rearranged to the transverse-longitudinal decompositions. Hilbert space of the real-valued functions of coordinates and time is chosen as a space of solutions. Complete set of the TE-time-domain modal waves is established and studied in detail. A continuity equation for the conserved energetic quantities for the time-domain modal waves propagating in the lossy waveguide is established. Instant velocity of transportation of the modal flux energy is found out as a function of time for any waveguide cross section. Fundamental solution to the problem is obtained in accordance with the causality principle. Exact explicit solutions are obtained and illustrated by graphical examples.
The reflection and transmission of electromagnetic waves obliquely incident on a uniaxial chiral slab with the optical axis perpendicular to the interface have been investigated. Firstly, the formulas of the reflection and transmission are derived. Then numerical results for four cases of the uniaxial chiral media are presented and different chiral parameters are considered. Finally, the Brewster's angles and total transmission are discussed.
Traditional optimization methods are not well suited for thinning large arrays to obtain a low sidelobe level (SLL). The chaotic binary particle swarm optimization (CBPSO) algorithm is presented as a useful alternative in the synthesis of thinned arrays. The proposed algorithm is improved by nonlinear inertia weight with chaotic mutation to increase the diversity of particles. Two examples have been proposed and solved. Simulation results compared with published results illustrate the effectiveness of the proposed method for both linear and planar arrays.
Although a Coherent Transponder (CT) is widely utilized in the field of Synthetic Aperture Radar (SAR), its Digital Elevation Model (DEM) has yet not been well studied for Interferometry SAR (InSAR). Based on the fact that the interferometry phase is a constant for CT with single transmit antenna, this paper mainly focuses on InSAR DEM induced by CT. The decorrelation effect in the intersection region of CT and nature terrain is researched in detail to support the analysis of CT's phase-unwrapping. The most important property, which makes DEM of CT being unique, is found to be the "slope" effect. The incline angel of "main slope" of DEM is verified to be determined only by the depression angle of InSAR system, whereas the incline angles of the "subordinate slopes" are affected by all the geometric parameters of InSAR baseline. Finally, all the incline angels are independent of CT' s waveform modulations, since the modulations have no contribution to the interferometry phase.
Geosynchronous Circular Synthetic Aperture Radar (GeoCSAR) has the Circular SAR configuration and undergoes a near-ellipse geosynchronous track rather a ``8''-like track of conventional GeoSAR. It could produce three dimensional (3-D) images of extended Earth scenes. GeoCSAR raw data simulator is of vital for predicting system performance, developing suitable data processing algorithms, etc.. It should include degrading conditions such as motion instability, angular deviations and orbit perturbations in order to approach the real situation. The common generation algorithm of raw data in time domain is precise but time-consuming for extended 3-D scene. In this paper, a novel raw data simulation algorithm based on inverse Improved Polar Format Algorithm (IPFA) for GeoCSAR was proposed, which possessed both the advantages of precision of time domain simulator and efficiency of frequency domain simulator. Implementation details were presented, and several simulation results were provided and analyzed to validate the algorithm.
Split ring resonator (SRR) can potentially be used as a design to be incorporated onto the truncated pyramidal microwave absorber. This study considers three different patterns of edge couple split ring resonator (EC-SRR) designs. Each EC-SRR design is then placed onto the truncated pyramidal microwave absorber. Outer split gap dimension widths of the EC-SRR are varied, and the various S21 performances are compared. This EC-SRR truncated pyramidal microwave absorber is simulated using CST Microwave Studio simulation software. The study and simulation are performed in low frequency range (0.01 GHz to 1 GHz) as well as in microwave frequencies range (1 GHz to 20 GHz). Simulation results of this EC SRR show improvement of reflection loss and S11 performance in the high frequency range of the pyramidal truncated microwave absorber.
In this paper, a new linear method for optimizing compact low noise oscillators for RF/MW applications will be presented. The first part of this paper makes an overview of Leeson's model. It is pointed out, and it is demonstrates that the phase noise is always the same inside the oscillator loop. It is presented a general phase noise optimization method for reference plane oscillators. The new method uses Transpose Return Relations (RRT ) as true loop gain functions for obtaining the optimum values of the elements of the oscillator, whatever scheme it has. With this method, oscillator topologies that have been designed and optimized using negative resistance, negative conductance or reflection coefficient methods, until now, can be studied like a loop gain method. Subsequently, the main disadvantage of Leeson's model is overcome, and now it is not only valid for loop gain methods, but it is valid for any oscillator topology. The last section of this paper lists the steps to be performed to use this method for proper phase noise optimization during the linear design process and before the final non-linear optimization. The power of the proposed RRT method is shown with its use for optimizing a common oscillator, which is later simulated using Harmonic Balance (HB) and manufactured. Then, the comparison of the linear, HB and measurements of the phase noise are compared.
An efficient model order reduction method for three-dimensional Finite Element Method (FEM) analysis of waveguide structures is proposed. The method is based on the Efficient Nodal Order Reduction (ENOR) algorithm for creating macro-elements in cascaded subdomains. The resulting macro-elements are represented by very compact submatrices, leading to significant reduction of the overall number of unknowns. The efficiency of the model order reduction is enhanced by projecting fields at the boundaries of macro-elements onto a subspace spanned by a few low-order waveguide modes. The combination of these two techniques results in considerable saving in overall computational time and memory requirement. An additional advantage of the presented method is that the reduced-order system matrix remains frequency-independent, which allows for very fast frequency sweeping and efficient calculation of resonant frequencies. Several numerical examples for driven and eigenvalue problems demonstrate the performance of the proposed methodology in terms of accuracy, memory usage and simulation time.
High speed analog-to-digital (A/D) sampling and a large amount of echo storage are two basic challenges of high resolution synthetic aperture radar (SAR) imaging. In this paper, a novel SAR imaging algorithm which named CS-MTMAB is proposed based on compressed sensing (CS) and multiple transmitters multiple azimuth beams (MTMAB). In particular, this new algorithm, which respectively reconstructs the targets in range and azimuth directions via CS technique, simultaneously provides a high resolution and wideswath two-dimensional map of the spatial distribution of targets with a significant reduction in the number of data samples beyond the Nyquist theorem and with an implication in simplification of radar architecture. The simulation results and analysis show that this new imaging scheme allows the aperture to be compressed and presents many important applications and advantages among which include reduced on-board storage constraints, higher resolution, lower peak side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR), less sampled data than the traditional SAR imaging algorithm, and also indicate that it has high robustness and strong immunity in the presence of serious noise. Finally, the real raw airborne SAR data experiment is performed to validate the proposed processing procedure.
In this work, we use the numerical steepest descent path (numerical SDP) method in complex analysis theory to calculate the highly oscillatory physical optics (PO) integral with quadratic phase and amplitude variations on the triangular patch. The Stokes' phenomenon will occur due to various asymptotic behaviors on different domains. The stationary phase point contributions are carefully studied by the numerical SDP method and complex analysis using contour deformation. Its result agrees very well with the leading terms of the traditional asymptotic expansion. Furthermore, the resonance points and vertex points contributions from the PO integral are also extracted. Compared with traditional approximate asymptotic expansion approach, our method has significantly improved the PO integral accuracy by one to two digits (10-1 to 10-2) for evaluating the PO integral. Moreover, the computation effort for the highly oscillatory integral is frequency independent. Numerical results for PO integral on the triangular patch are given to verify the proposed numerical SDP theory.
This paper presents an extended delay-rational macromodel for electromagnetic interference analysis of mixed signal circuits. Firstly, an S-parameter matrix based delay-rational macromodel of the associated microwave network or system is established. Then, we extend the macromodel to include the external electromagnetic interference effects. The forced waves induced by the excitation fields are computed using full-wave method and treated as additional equivalent sources. Next, the macromodel is modified to embed the additional sources at each corresponding port. Finally, the resulting macromodel is converted into equivalent circuit for circuit analysis with the corresponding linear and non-linear port terminations. Several examples are computed by using the proposed method and the numerical results are compared with those obtained by 3-D FDTD method only. They are all in a good agreement that validate this method.
A multilayer dual-mode complementary filter is developed based on substrate integrated circular and elliptic cavity (SICC and SIEC) in this paper. The filter is constructed with two different kinds of cavities, and each cavity supports two degenerate modes, which can be generated and controlled by the coupling aperture and slot located between layers. Detailed design process is introduced to synthesize an X-band dual-mode complementary filter. It not only has good performance, but also reduces the circuit size much more. Moreover, Sharp transition characteristic both in the lower and upper sidebands demonstrates high selectivity of the filter. Good agreement is obtained between the simulated and measured results of the proposed structure.
Linear magnetic gears take the definite merit of direct force amplification or speed reduction without using any bulky, inefficient rotary-to-linear mechanism. In this paper, an analytical calculation approach to determine the performance of linear tubular magnetic gears is proposed. The key is to adopt the concept of anisotropic magnetic permeability to handle the field-modulation region which consists of iron rings and airspaces in a zebra-striped manner. By solving the Laplace's and Poisson's equations in the linear tubular magnetic gear, the corresponding magnetic field distributions can be analytically determined. Finally, the analytical calculation results are compared with the numerical results obtained from the finite element method, hence verifying the validity of the proposed analytical field calculation.
A new adaptive beamforming technique based on neural networks (NNs) is proposed. The NN training is accomplished by applying a novel optimization method called Mutated Boolean PSO (MBPSO). In the beginning of the procedure, the MBPSO is repeatedly applied to a set of random cases to estimate the excitation weights of an antenna array that steer the main lobe towards a desired signal, place nulls towards several interference signals and achieve the lowest possible value of side lobe level. The estimated weights are used to train efficiently a NN. Finally, the NN is applied to a new set of random cases and the extracted radiation patterns are compared to respective patterns extracted by the MBPSO and a well-known robust adaptive beamforming technique called Minimum Variance Distortionless Response (MVDR). The aforementioned comparison has been performed considering uniform linear antenna arrays receiving several interference signals and a desired one in the presence of additive Gaussian noise. The comparative results show the advantages of the proposed technique.
A novel basis function, called as the Modified Phase Extracted (MPE) basis function, has been proposed to analyze three-dimensional scattering problems for electrically large, thin dielectric-coated targets. The MPE basis function, which can be defined on large (e.g., a wavelength or more) curvilinear geometrical elements, is developed for quadrilateral cells. Consequently, combining with the thin dielectric sheet (TDS) approximation, the MPE basis function solves the scattering problem accurately with fewer unknowns than the solutions based on the conventional basis functions. In order to improve the accuracy of the solution solving the problem which has thicker dielectric coatings, some modifications about the TDS approximation model are made. Numerical examples demonstrate that the validity of the proposed approach in solving the scattering from electrically large, thin coated objects.
The capabilities and operation of electromagnetic devices can be dramatically enhanced if artificial materials that provide certain prescribed properties can be designed and fabricated. This paper presents a systematic methodology for the design of dielectric materials with prescribed electric permittivity. A gradient-based topology optimization method is used to find the distribution of dielectric material for the unit cell of a periodic microstructure composed of one or two dielectric materials. The optimization problem is formulated as a problem to minimize the square of the difference between the effective permittivity and a prescribed value. The optimization algorithm uses the adjoint variable method (AVM) for the sensitivity analysis and the finite element method (FEM) for solving the equilibrium and adjoint equations, respectively. A Heaviside projection filter is used to obtain clear optimized configurations. Several design problems show that clear optimized unit cell configurations that provide the prescribed electric permittivity can be obtained for all the presented cases. These include the design of isotropic material, anisotropic material, anisotropic material with a non-zero off-diagonal terms, and anisotropic material with loss. The results show that the optimized values are in agreement with theoretical bounds, confirming that our method yields appropriate and useful solutions.
Microstrip patch antennas have several advantages over conventional antennas including their low profile structure, light weight and low cost. As such, they have been widely used in a variety of applications. However, one of the major drawbacks of this antenna is the low bandwidth. In this paper, bandwidth of a dual patch antenna is improved by etching dummy EBG pattern on the feedline. Effects of different positions of the feedline on the bandwidth are also studied. A good improvement in bandwidth for the antenna with the dummy EBG pattern when compared to the reference antenna is obtained for all the feedline positions.
This paper reports the modeling and characterization of interdigitated rows of carbon nanotube electrodes used to address a liquid crystal media. Finite Element Method modeling of the nanotube arrays was performed to analyze the static electric fields produced to find suitable electrode geometry. A device was fabricated based on the simulation results and electro optics characteristics of the device are presented. This finding has applications in the development of micron and submicron pixels, precise beem steering and nanotube based active back planes.
This paper discusses computation of shape derivatives of electromagnetic fields produced by complex 2-periodic structures. A dual set of forward and adjoint problems for Maxwell's equations are solved with the method of moments (MoM) to calculate the full gradient of the object function by the adjoint variable method (AVM). The periodic fast multipole method (pFMM) is used to accelerate the solution of integral equations for electromagnetic scattering problems with periodic boundary conditions (PBC). This technique is applied to shape optimization problems for negative-index metamaterials (NIM) with a double-fishnet structure. Numerical results demonstrate that the figure of merit (FOM) of metamaterials can reach a maximum value when the shape parameters are optimized iteratively by a gradient-based optimization method.
An analytical model is presented to investigate the performances of an annular-ring patch etched on a two layered dielectric substrate and is covered by a dielectric superstrate, by using a full-wave spectral domain technique in conjunction with the complex resistive boundary condition. Galerkin's method and Parseval's theorem are used to obtain the resonant frequency and bandwidth. To validate the theoretical results, a study has been performed for an annular-ring patch on a single layer, with air gap, and cover layer. The computed data are found to be in good agreement with results obtained using other methods. Variations of the resonant frequency and bandwidth with the high temperature superconducting (HTS) thin film are also presented. The proposed model is simple, accurate and thus should help a designer for practical applications.
PIN diodes are used to electronically switch a rectangular microstrip antenna between the optimal radiation state and the low radar cross section (RCS) state in this paper. A useful loading circuit is proposed. The circuit is connected between the patch and the ground plane of the antenna at each loading position. The loading positions of the circuit are determined by studying magnitude distributions of the induced electric field and analyzing statistically how many times that the maximum electric field occurs in each area for each discussed incident angle. PIN diodes are equivalent to capacitances and resistances when diodes are reverse-biased and forward-biased, respectively. When the antenna is not in service and excited by an incident plane wave, obvious RCS reduction is realized. In addition, the radiation performances are well maintained when the antenna is in service for transmitting or receiving signals.
This study focuses on electromagnetic and thermo-mechanical optimal design for high-temperature broadband radome wall with symmetrical graded porous structure. The position-dependent porosity increases from the two surfaces of the structure to its intermediate layer. Electromagnetic and thermo-mechanical properties of the proposed structure are investigated simultaneously via numerical simulations. Optimal results suggest that the symmetrical porous structure possesses better broadband transmission performance in the 1-100 GHz frequency range, in contrast to a traditional A-sandwich structure. The thermo-mechanical investigation also indicates that the novel structure meets the requirement for high-temperature (up to 1400°C) applications.
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