Ultra Wide Band Antennas

Chapter 2

Radiation Characteristics of Antennas ¹

2.1. Introduction

Antenna designers are frequently confronted with two types of approach. The first where we describe their characteristics with the Maxwell’s equations and the assistance of operators like Hertz’s potential [STR 61], led to long calculations and was often not very instructive. In the second, a hand-waving approach using some formulas is more intuitive but often limited to well-known examples that cannot be easily generalized [LIZ 04].

In this chapter, we focus on the unified and rigorous approach of antenna design which was proposed by Per-Simon Kildal [KIL 99]. We will endeavor to reveal the physical phenomena characterizing the behavior of the antennas thanks to a compact formulation. The objective is to define all of the radiation characteristics which thereafter will be used and developed within the framework of ultra wide band (UWB) applications. As we will see in the following, a UWB antenna can be analyzed in the frequency and time domains and the discussion thread of this work is to present and connect these two domains. For an exhaustive and more academic presentation of the radiation characteristics of antennas, the authors propose to consult the following reference [BAL 05] which presents a conventional and well established formulation of the antenna theory. After defining the usual characteristics of the antennas, we will show an example of conventional characterization of a UWB antenna. This last part ...