Freddy Gardiol

An Overview of Integral Equation Techniques Applied to Microstrip Antenna Design

In the past decade, microstrip planar structures and, in particular, microstrip antennas have found an increasing number of applications which span a very large field, ranging from biomedical diagnosis to satellite radiocommunications. This popularity, added to the fact that microstrip geometry is relatively simple, has turned microstrip analysis into a cornerstone problem to which almost every mathematical technique currently used in electromagnetics has been applied. This is witnessed by a huge amount of technical litterature and several monographic books published in recent years [1-3].

Radar Cross Section Computation of Microstrip Patches

ABSTRACT The paper presents a method for the computation of the radar cross section of microstrip patches. The approach is based on a combination of ideas derived from the mixed potential integral equation formulation for microstrip antennas, fast convolution algorithms and the biconjugate gradient iterative method. All operations are kept at a vector level and this renders the method capable of handling a large number of unknowns. Numerical results for a rectangular and a circular patch have been compared with measured results available in literature and a good agreement has been observed. Advantages and limitations are discussed.

Techniques analytiques et numériques dans l'analyse des antennes microruban

AnalyseCet article considère les antennesplaques de forme quelconque en microruban et leur analyse théorique. Il décrit les principaux modèles simplifiés utilisés jusqu’à maintenant, puis présente une méthode mathématique rigoureuse, qui fait usage des fonctions dyadiques de Green pour milieux stratifiés. Les noyaux des intégrales obtenues possèdent des singularités et un comportement divergent. Un procédé de calcul original permet leur intégration. L’antenneplaque est ensuite découpée en rectangles, sur lesquels les courants de surface sont déterminés par une méthode de moments. L’impédance d’entrée est calculée, puis comparée à des valeurs expérimentales.AbstractThis paper deals with microstrip patch antennas of arbitrary shape, and techniques available for their analysis. It reviews the various approximate models utilized so far, and presents a rigorous mathematical approach, based on dyadic Green’s functions for stratified media. Integrals are obtained with integrands possessing both singularities and a divergent behaviour at infinity: a numerical technique was set up for their integration. The antenna patch is cut up in rectangles, over which the surface currents are evaluated by a moment’s method. The antenna’s input impedance is computed and compared with measured values.

Equivalent Inductance and Capacitance of a Microstrip Slot

Slots cut in the upper conductor of a microstrip transmission line have been used to match microwave components such as couplers and filters. Their equivalent circuit, which must be known in order to design devices involving such discontinuities, is composed of a series inductance and of capacitances. These elements are determined, in terms of the geometrical parameters, by means of a quasistatic analysis, assuming TEM-mode propagation on a lossless line.

Surface Wave Fields and Efficiency of Microstrip Antennas

Description of the two first surface wave modes (TM0 , TE1) and the computation of the associated fields. From the values of the fields, it is easy to calculate the Poynting vector and, hence, the associated powers. Once the powers associated with the space wave and the surface wave are known, it is possible to define a efficiency.

Radome Effects on Microstrip Antenna Parameters

Greens function for microstrip two-layer cases are studied and determined. Radome effects on microstrip antenna parameters are presented. Numerical results for rectangular patches are compared with experiment for several values of dielectric constant and radome thickness.

TE11 Reflection of Open-Ended Circular Waveguides Application to Nondestructive Measurement of Materials

The measurement of dielectric properties of a material based on the reflection of an open-ended waveguide is a simple and nondestructive technique, which does not require to extract any sample of the material to be measured. It is therefore of interest in biomedical applications, and also in the study of the moisture content of materials. The material one wishes to measure is placed on a metallic flange which terminates the open-ended waveguide, directing the radiation within the material. The theoretical study of the problem is based upon the determination of the radiated magnetic field near the aperture, determined in terms of the transverse electric field in the plane of the aperture. An integral relationship can be elaborated, linking the relative permittivity of the material to the reflection coefficient of the propagation mode in the circular waveguide. The same technique can be used to determine the fields radiated by a diathermy applicator.

Polarization State and Input Impedance of Arbitrarily Shaped Microstrip Antennas

Microstrip antennas have been widely used during the past three decades due to mechanical and economical advantages. But the associated electromagnetic problems present considerable difficulty. Therefore, theoretical models putting on solid foundation the previous empirical design were only introduced in the last decade. The rigorous analysis of a microstrip antenna involves the solution of an electric integral equation (EFIE) , whose kernel must account for the effect of the dielectric slab [1,2,3].

Analysis of Microstrip Antenna Arrays with Thick Subtrates

An accurate microstrip coaxial feed model is introduced that is valid for substrates of arbitrary thickness. The Method of Moments is employed using basis functions on each of the patches of the array and on the coax feed probes. Special attachment modes are used at the coax/patch junction. Mutual coupling in small arrays is studied.

An Analysis of Arbitrarily Shaped Microstrip Antennas Including Surface Wave Effects

The accurate determination of surface currents in microstrip planar antennas requires the solution of a two-dimensional singular integral equation of electric type (EFIE). The first problem encountered when solving this equation numerically, is the obtention of a fast and accurate algorithm for evaluating its kernel. This kernel is given by a combination of Sommerfeld-like integrals where the surface wave phenomena are automatically included, and standard computer integration routines are unable to evaluate it. A second problem is the implementation of an efficient moment method. This task is very delicate because the kernel is singular. In particular, the self (diagonal) terms of the moment matrix must be carefully evaluated. Also, the modelling of the coaxial feed probe offers considerable difficulties which have been overcame by using Richmonds reaction method. This paper presents a coherent numerical approach to solve these problems and to calculate the current distribution in microstrip antennas of arbitrary shape.