An Analytic Continuation Method for the Ultra Broadband Determination of the Electromagnetic Properties of Materials

Abstract

All dielectric materials, by nature, exhibit a frequency dependent permittivity. This property, termed dispersion, must be taken into account when materials are employed in applications that span very broad frequency ranges; such as ultra-wideband antenna applications and the design of Low Observable structures. Therefore, an accurate and compact representation of this frequency dependence over very broad bands of frequencies is needed In addition, Time Domain Computational Electromagnetics computer codes can only realize their full potential when such a representation is used for modeling of material bodies, since only then will the pulse solution truly contain the proper solutions for the full spectrum of the pulse. Such a representation can be developed¹ by using the analytic function properties of the permittivity and a minimum set of physical assumptions. The result is a compact sum of special analytic basis functions. Because of their analyticity, dielectric data obtained over convenient portions of the Radio Frequency spectrum can be continued into other portions of the spectrum where measurements may be more difficult to perform. The usefulness of this technique is illustrated by generating the ultra broadband model of a carbon loaded absorbing foam of the type used in anechoic chambers. The model is then incorporated into a Dispersive Finite Difference Time Domain calculation of the absorption performance of a wall covered by wedges of that foam.