Physical Knowledge Based Scalable Phased Array Antenna Modeling for Radar Systems

The development of a large-scale phased array radar system such as the future MPAR will need a cost-effective tool for predicting electromagnetic characteristics of antennas. Simulating and optimizing of large finite phased array antennas using commercially available solvers are time-consuming and memory-extensive even though they are highly capable of solving general electromagnetic problems with acceptable accuracy. In this work, a full-wave electromagnetic solver based on finite-difference time-domain (FDTD) method has been developed for simulating phased array antennas. The planar array or array element can be simulated, optimized, or analyzed using FDTD theory based on an orthogonal, regular Cartesian lattice. The FDTD updating equation for diagonally anisotropic material was obtained for periodic structure based on the cylindrical coordinate system. This FDTD algorithm can be used to simulate active element patterns of conformally cylindrical array antennas. The simulation of active element patterns in an infinite faceted-cylindrical array was accomplished with a nonorthogonal and unstructured grid. The derivation of FDTD theory and periodic boundary condition for a structure based on the nonorthogonal and unstructured grid is presented. In this work, two simulation schemes, which are based on computed near-field current density information and the physical knowledge of finite array antennas, were presented for predicting broadside array radiation characteristics with the consumption of relatively low computational resources. The validation of the simulation program and schemes was fulfilled by comparing simulation results with measurements taken by near-field and far-field techniques

FDTD-based full wave co-simulation model for hybrid electromagnetic systems

In high-frequency ranges, the present electronic design automation software has limited capabilities to model electromagnetic (EM) systems where there are strong field effects influencing their characteristics. In this situation, a full-wave simulation tool is desired for the analysis and design of high-speed and non-linear EM systems. It is necessary to explore the interaction between the field and electronic components during a transient process when field effects are more significant. The finite-difference time-domain (FDTD) technique receives growing attention in the area of EM system analysis and simulation due to its simplicity, flexibility and robustness. It is a full-wave simulation method that solves the Maxwell\u27s equations in time domain directly. Decades of research and development and rapid growth in computer capability have built up a firm foundation for FDTD techniques to be applied to many practical problems. Based on FDTD, this dissertation develops a stable CO-simulation method to perform a full-wave simulation of a hybrid EM system consisting of lumped elements and distributed structures. In this method, FDTD is used to solve the EM field problems associated with distributed structures, and a circuit simulator solves the response of lumped elements. A field-circuit model proposed in the dissertation serves as the interface between the two simulation tools. Compared with previous methods, the FDTD method based on this model is much more flexible and stable for linear and nonlinear lumped elements under both small and large signal conditions. Because of its flexibility and robustness, this model is a promising approach to integrate a field solver and a circuit simulator in the simulations of practical EM systems. In order to improve the simulation accuracy, some problems related to FDTD simulation are studied. Based on the numerical dispersion in homogeneous media uniform grids, the FDTD numerical reflection and transmission on the boundary of media, which are discritized by a non-uniform grid, are investigated. This investigation provides for the first time an estimation of FDTD numerical error in inhomogeneous media and non-uniform grids. Perfectly matched layer (PML) was previously utilized the homogeneous media or uniform grids. This dissertation extends the PML boundary conditions to handle the inhomogeneous media and non-uniform grid. Techniques extracting S parameters from FDTD simulation are also discussed. Two and three-dimensional CO-simulation software, written in C++, has be derived, developed and verified in this dissertation. The simulation results agree well with results from other simulation methods, like SPICE, for many test circuits. Taking data sampling and interpolation into account, simulation results generally fit well to measurement and other simulation results for complicated three-dimensional structures. With further improvements of the FDTD technique and circuit simulation, field-circuit CO-simulation model will widen its application to general EM systems

Direct and Inverse Computational Methods for Electromagnetic Scattering in Biological Diagnostics

Scattering theory has had a major roll in twentieth century mathematical physics. Mathematical modeling and algorithms of direct,- and inverse electromagnetic scattering formulation due to biological tissues are investigated. The algorithms are used for a model based illustration technique within the microwave range. A number of methods is given to solve the inverse electromagnetic scattering problem in which the nonlinear and ill-posed nature of the problem are acknowledged.Comment: 61 pages, 5 figure

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3 and reports on seven research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Contract ECS 86-20029Schlumberger- Doll ResearchU.S. Army Research Office Contract DAAL03 88-K-0057National Aeronautics and Space Administration Contract NAGW-1617U.S. Navy - Office of Naval Research Contract N00014-89-J-1107National Aeronautics and Space Administration Contract NAGW-1272National Aeronautics and Space Administration Contract 958461Simulation Technologies Contract DAAH01-87-C-0679U.S. Army Corp of Engineers Contract DACA39-87-K-0022WaveTracer, Inc.U.S. Navy - Office of Naval Research Contract N00014-89-J-1019U.S. Air Force Systems - Electronic Systems Division Contract F19628-88-K-0013Digital Equipment CorporationInternational Business Machines CorporationU.S. Department of Transportation Contract DTRS-57-88-C-0007

Design & Optimization of Large Cylindrical Radomes with Subcell and Non-Orthogonal FDTD Meshes Combined with Genetic Algorithms

The word radome is a contraction of radar and dome. The function of radomes is to protect antennas from atmospheric agents. Radomes are closed structures that protect the antennas from environmental factors such as wind, rain, ice, sand, and ultraviolet rays, among others. The radomes are passive structures that introduce return losses, and whose proper design would relax the requirement of complex front-end elements such as amplifiers. The radome consists mostly in a thin dielectric curved shape cover and sometimes needs to be tuned using metal inserts to cancel the capacitive performance of the dielectric. Radomes are in the near field region of the antennas and a full wave analysis of the antenna with the radome is the best approach to analyze its performance. A major numerical problem is the full wave modeling of a large radome-antenna-array system, as optimization of the radome parameters minimize return losses. In the present work, the finite difference time domain (FDTD) combined with a genetic algorithm is used to find the optimal radome for a large radome-antenna-array system. FDTD uses general curvilinear coordinates and sub-cell features as a thin dielectric slab approach and a thin wire approach. Both approximations are generally required if a problem of practical electrical size is to be solved using a manageable number of cells and time steps in FDTD inside a repetitive optimization loop. These approaches are used in the full wave analysis of a large array of crossed dipoles covered with a thin and cylindrical dielectric radome. The radome dielectric has a thickness of ~λ/10 at its central operating frequency. To reduce return loss a thin helical wire is introduced in the radome, whose diameter is ~0.0017λ and the spacing between each turn is ~0.3λ. The genetic algorithm was implemented to find the best parameters to minimize return losses. The inclusion of a helical wire reduces return losses by ~10 dB, however some minor changes of radiation pattern could distort the performance of the whole radome-array-antenna system. A further analysis shows that desired specifications of the system are preserved

Selected developments in computational electromagnetics for radio engineering

This thesis deals with the development and application of two simulation methods commonly used in radio engineering, namely the Finite-Difference Time-Domain method (FDTD) and the Finite Element Method (FEM). The main emphasis of this thesis is in FDTD. FDTD has become probably the most popular computational technique in radio engineering. It is a well established, fairly accurate and easy-to-implement method. Being a time-domain method, it can provide wide-band information in a single simulation. It simulates physical wave propagation in the computational volume, and is thus especially useful for educational purposes and for gaining engineering insight into complicated wave interaction and coupling phenomena. In this thesis, numerical dispersion taking place in the FDTD algorithm is analyzed, and a novel dispersion reduction procedure is described, based on artificial anisotropy. As a result, larger cells can be used to obtain the same accuracy in terms of dispersion error. Simulation experiments suggest that typically the dispersion reduction allows roughly doubling the cell size in each coordinate direction, without sacrificing the accuracy. The obtainable advantage is, however, dependent on the problem. In the open literature, a few other procedures are also presented to reduce the dispersion error. However, the rather dominating effect of unequal grid resolution along different coordinate directions has been neglected in previous studies. The so-called Perfectly Matched Layer (PML) has proven to be a very useful absorbing boundary condition (ABC) in FDTD simulations. It is reliable, works well in wide frequency band and is easy to implement. The most notable deficiency of PML is that it enlarges the computational volume - in open 3-D structures easily by a factor of two. However, due to its advantages, PML has become a standard ABC. In this thesis, the operation of PML in FDTD has been studied theoretically, and some interesting properties of it not known before are uncovered. For example, it is shown that, surprisingly, PML can absorb perfectly (i.e. with zero reflection) plane waves propagating towards almost arbitrary given direction at given frequency. Optimizing the conductivity profile allows reduction of the PML thickness. A typical application of the FDTD method is the design of a mobile handset antenna. An improved coaxial probe model has been developed for antenna simulations. The well-known resistive voltage source (RVS) model has also been discussed. A reference plane transformation is proposed to correct the simulated input impedance. A popular thin-wire model in 2-D FDTD is discussed, and it is shown to be based on erroneous reasoning. The error has been corrected by a simple procedure, and the corrected model has been demonstrated to simulate infinite long thin wires much better than the commonly used model. A novel way to implement singular basis functions in FEM is discussed. It is shown theoretically and demonstrated by examples that if a waveguide propagation mode contains field singularities, then explicit inclusion of singularities in finite element analysis is crucial in order to obtain accurate cut-off wavenumbers.reviewe

Dispersion analysis of two-dimensional unstructured transmission line modelling (UTLM)

Numerical simulation techniques play an important role due to their flexibility in dealing with a broad range of complex geometries and material responses. This flexibility requires substantial computational time and memory. Most numerical methods use structured grid for graphical discretization, although this approach is straightforward it is not ideal for smoothly curved boundaries. In this thesis the two-dimensional Transmission Line Modelling (TLM) method based on unstructured meshes is adopted. TLM is an established numerical simulation technique that has been employed in a variety of applications area. Using unstructured meshes to discretize the problem domain permits smooth boundary presentation which provides significant enhancement in the flexibility and accuracy of the TLM simulations. An algorithm is developed to implement Unstructured Transmission Line Modelling (UTLM) which is carefully designed for simplicity and scalability of model size. Several examples are employed to test the accuracy and efficiency of the UTLM simulations. Delaunay meshes, as a type of unstructured meshes, provide good quality triangles but have the disadvantage of providing close to zero transmission line length which has impact on the maximum permissible time step for stable operation. In this thesis, a simple perturbation method for relaxing the minimum link length and clustering triangles in pairs is presented, which permits substantial increase in time step and hence computational runtime to be made without compromising the simulation stability or accuracy. Also, a new model for relaxing the short link lines that fall on the boundaries is presented. UTLM method is based on temporal and spatial sampling of electromagnetic fields which results in dispersion. In this thesis, dispersion characteristics of the unstructured TLM mesh are investigated and compared against structured TLM results for different mesh sizes and shapes. Unlike the structured TLM mesh, the unstructured mesh gives rise to spatial mode coupling. Intermodal coupling behaviour is investigated in a statistical manner upon the change of the mesh local characteristics