Michael S. Kluskens

A Toolset Independent Hybrid Method for Calculating Antenna Coupling

Calculation of the electromagnetic interference (EMI) between electrically large antennas mounted on ships is important for a variety of Navy problems. This paper presents a toolset independent hybrid method for calculating the power at receive antenna terminals relative to the power incident on transmit antenna terminals. The hybrid method coupling results are validated against full-wave computational electromagnetic (CEM) simulations and measurements. An advantage of the proposed hybrid approach is that CEM calculations for antenna near-fields and propagation between antennas can be executed with user-preferred tools. In addition, transmit and receive antenna calculations are executed in transmit mode independent of ship structures. Thus, antenna calculations can be stored in a library for calculation reuse and optimization of antenna placement for EMI reduction.

Analytical evaluation of Sommerfeld integral tails for layered-media Green's functions

Greens functions for layered media find applications in analysis of radar cross sections, radiation problems for array sources embedded within complex materials, prediction of electric fields from lightning, remote sensing, shipborne EMI/EMC issues and other various applications. Central to the predictions, for such applications, is the need for accurate evaluation of the appropriate Greens functions that contain Sommerfeld integrals. In this paper a method is proposed for direct, real-axis integration of Sommerfeld integrals, obviating the calculation of pole locations and their residue contributions, with the integral tail evaluated analytically in closed form. The computational efficiency of the proposed algorithm is illustrated here with preliminary results by analyzing the Gzx component of the Greens function for a HED inside a PEC-backed, double-layer dielectric media. Finally, the present method appears to be better amongst other similar approaches because it can better model the inhomogeneity of the constitutive electrical parameters in the vertical direction of the PEC-backed layered structure.

A new approach for improved evaluation of sommerfeld integral tails for PEC-terminated single layered media

Sommerfeld integrals [1] appearing in the Greens function for layered media pose significant challenges in computation of the tail part of the integrand when the observer and source locations have large lateral separations with the observer close to the interface(s) [2]-[5]. Analytical [3],[4] and novel numerical [5] methods have been utilized to circumvent such problems, and is the subject of this paper. The purpose of this investigation is to obtain improved analytical forms for closed-form evaluation of the Sommerfeld integral tail that are more general compared to [3],[4].

Some new techniques for evaluating Sommerfeld integrals for microstrip antenna analysis

A new transformation for evaluating Sommerfeld integrals is derived here when the path is deformed in the upper half of the complex plane. This transformation has the feature that as the lateral separation ρ → ∞, the argument of the Bessel function diminishes. It is argued that this approach shall facilitate much efficient calculation of Sommerfeld integrals.

Numerical comparison of exact and asymptotic methods for Sommerfeld integral evaluation with applications to microstrip antennas

In this paper a new method for evaluating Sommerfeld integrals for arbitrary source and receiver location pairs, for a horizontal electric dipole (HED) located at the air-dielectric interface of a PEC-terminated dielectric media, is described. The proposed method is valid for both large and small lateral separations, and for arbitrary receiver locations. Unlike past investigations, the proposed method avoids location, and associated residue calculation of the poles of the integrand through deforming a part of the real-axis in the upper half plane that is free from any pole singularities of the Sommerfeld integrand. Compared to an earlier investigation reported by the present authors, the present approach includes situations when both the source and receiver are exactly on the interface.

A new algorithm for the complex exponential integral in the method of moments

This paper presents a new algorithm for the rapid and accurate calculation of the complex exponential integral associated with the mutual impedance of sinusoidal basis and testing functions in the method of moments. The new algorithm uses Leibnizs theorem to calculate Taylor series expansions of the integral instead of integrating expansions of the integrand as is often done. This results in an algorithm which is twice as fast as and is valid over a wider range than previous algorithms. This technique can be applied to many other integrals encountered in computational electromagnetics as well.

An efficient hybrid CEM approach to modeling backscatter of forest clutter

We present a novel hybrid Computational Electromagnetics (CEM) modeling framework for simulating the backscatter from forest clutter when sensed by UHF and VHF radars. Previous approaches have pointed to the need for hybrid computational modeling, combining PO and GO techniques. In this paper, we identify a novel approach offering superior fidelity and computational efficiency in calculating the backscatter from forest clutter and demonstrate preliminary results.

Some investigations toward closed-form solutions of sommerfeld integrals

Sommerfeld integrals, that appear in problems related to electromagnetic wave propagation through layered media, have been traditionally evaluated by locating the poles of the integrand and accounting for their corresponding residue contributions. For multilayer problems, implementation of this procedure could potentially become computationally inefficient because the number of poles with significant residue contributions increases with frequency or equivalently the electrical thickness of the individual layers. This observation suggests that the well-known and popular discrete complex image method (DCIM) could also need significant modifications to its conventional algorithmic implementation for electrically thick layers.

Numerical assessment of uniform asymptotic solutions for a class of Sommerfeld integrals for microstrip antenna problems

Uniform asymptotic solution of Sommerfeld integrals for microstrip antenna problems, related to topologies with single- or double-layered dielectrics backed by a perfect electric conductor (PEC), are most suitable for electrically large problems. In this context a numerical comparison of Sommerfeld integrals evaluated by asymptotic and rigorous methods is presented. The focus of this comparison is to assess the numerical accuracy of the asymptotic solution for electrically small lateral separations with applications to mutual coupling between elements in densely packed microstrip antenna arrays. The two methods of evaluation are also distinct because the uniform asymptotic method requires TM0 proper surface wave pole contribution, while the alternate rigorous approach is immune from considering surface wave pole effects. Preliminary results for single-layer geometry,included here, show that the uniform asymptotic solution remains remarkably accurate even for small lateral separations (ρ over λ ≈ 0.3).

The Role of Mutual Coupling in A 5:1 Bandwidth Stripline Notch Array

The bandwidth broadening effects of time-domain mutual coupling from adjacent elements in a linear array of stripline notch elements was briefly described in previous papers1, 2, 3. The array was designed at the Naval Research Laboratory (NRL) to demonstrate the feasibility of 5:1 bandwidth wide-scan angle arrays with one-half wavelength spacing at the highest operational frequency. This paper presents an expanded examination of the role of mutual coupling in pulse-excited linear and planar single polarization arrays as well as in a planar dual polarization array. When viewed in the time domain, inspection of mutual coupling leads to a physical understanding of the cause of the ultrawideband (UWB) behavior of the NRL arrays. The finite-difference time-domain (FDTD) method4,5 is employed to perform the studies, and measurements verify some of the calculations.