Some basic guidelines for miniaturizing UWB antennas

The purpose of the paper is to discuss broadband antenna miniaturization in general. The goal is to illustrate some simple guidelines that can used for miniaturizing a broadband antenna. To demonstrate these guidelines, we use a wire log-spiral antenna which is miniaturized via inductive loading. In this case, the inductive loading is achieved without modifying the antenna structure by increasing the self inductance of the wire segments from which form the spiral. This is readily accomplished using a method of moments code such as NEC which allows the user to assign a distributed or lumped impedance to each wire segment. Therefore, the phase velocity can be arbitrarily reduced depending upon the inductance per unit length. Using this approach, we discuss two important guidelines for miniaturizing an UWB antenna such as a spiral. The first is in determining how much the antenna should be miniaturized. Secondly, we examine how the loading profile impacts the performance of a spiral antenna.