Doruk Tayli

Physical bounds of antennas

Design of small antennas is challenging because fundamental physics limits the antennas performance. Physical bounds provide basic restrictions on the antenna performance solely expressed in the available antenna design space. These bounds offer antenna designers a priori information about the feasibility of antenna designs and a figure of merit for different antenna designs. Here, an overview of physical bounds on antennas and the development from circumscribing spheres to arbitrary shaped regions and embedded antennas are presented. The underlying assumptions for the methods based on circuit models, mode expansions, forward scattering, and current optimization are illustrated and their pros and cons are discussed. The physical bounds are compared with numerical data for several antennas. (Less)

Energy Stored by Radiating Systems

Though commonly used to calculate Q-factor and fractional bandwidth, the energy stored by radiating systems (antennas) is a subtle and challenging concept that has perplexed researchers for over half a century. Here, the obstacles in defining and calculating stored energy in general electromagnetic systems are presented from first principles as well as using demonstrative examples from electrostatics, circuits, and radiating systems. Along the way, the concept of unobservable energy is introduced to formalize such challenges. Existing methods of defining stored energy in radiating systems are then reviewed in a framework based on technical commonalities rather than chronological order. Equivalences between some methods under common assumptions are highlighted, along with the strengths, weaknesses, and unique applications of certain techniques. Numerical examples are provided to compare the relative margin between methods on several radiating structures.

Synthesis of Large Endfire Antenna Arrays Using Convex Optimization

An innovative approach utilizing convex optimization to simultaneously conduct pattern synthesis and improve the matching of large-scale endfire antenna arrays is proposed in this paper. A fast full-wave analysis tool facilitates the computation of the necessary data for running the optimization routine and enables analysis on arrays with dimensions

Numerical benchmark based on characteristic modes of a spherical shell

100\lambda \times 6\lambda

A Comparison of Macro Basis Function Methods for Interconnected Endfire Antenna Arrays

for the highest simulated frequency. Simulated results are provided for various array configurations of bowties, and the results show that improved matching can be obtained while maintaining a clear endfire far-field pattern analogous to the pattern obtained with the classical Hansen–Woodyard excitation. The spatial dependence on the amplitude of the optimized input waves in the antenna ports indicates that a considerable fraction of the input power is fed to the antennas at the array’s front, in the direction in which the main lobe is launched.

On the issue of simulating very large endfire arrays with complex antenna geometries

Characteristic modes of a spherical shell are found analytically and compared with numerical solutions acquired from both in-house and commercial packages. These studies led to a proposal of several independent benchmarks, all with analytically known results. Dependence on mesh size, electrical size and other parameters can easily be incorporated. It is observed that all contemporary implementations have limitations.

Calculating the physical bounds for antennas above a ground plane

Two approaches to the macro basis function (MBF) method that target interconnected subdomains have been adapted to finite linear arrays, and benchmarked against each other in order to estimate their performance with respect to the strong near field coupling that occurs under the endfire mode operation. The methods, here referred to as methods A and B, are based on the synthetic function and characteristic basis function method, respectively, presented in the previous literature. The occurrence of very strong near-field coupling can be seen to affect the number of MBFs required for a certain level of accuracy, although both approaches perform well under the test scenario. However, method B provides a considerably more efficient compression with respect to a maximum acceptable error level.

Q factors for antennas in dispersive media

This paper discusses some of the main issues of efficient analysis of electrically very large endfire arrays, and further proposes approaches for developing flexible simulation tools for this particular purpose. Some initial results supporting the endfire array design issue are presented, as well as some preliminary examples of implemented compression- and acceleration methods.

Antenna Current Optimization using MATLAB and CVX

The physical bounds for antennas above a ground plane is analyzed in this paper. Optimal antenna G/Q ratio and Q factor are calculated using convex optimization from stored electric and magnetic energy matrices, obtained from a method of moments solver. Physical bounds for a patch antenna with different heights above a ground plane are investigated. Results are verified using commercially available electromagnetic solver FEKO.