TABLE OF CONTENTS Frequency-independent antennas form a relatively mature, well-understood, and appreciated family of UWB antennas. These antennas are discussed in their historical contexts in Section 1.1.3. Frequency-independent antennas rely on an angle invariant scaling from a small-scale portion, which defines the high-frequency limit, to a large-scale portion, which defines the low-frequency limit. This property of frequency-independent antennas has significant advantages as well as disadvantages. The principal advantage is that bandwidth is limited only by the range of scaling physically achievable in antenna construction. Thus, a decade or more of bandwidth is possible. The principal disadvantage is that this same distributed scaling gives rise to the dispersion documented in Section 2.2.1.
Some of the more common frequency-independent antennas include spirals, conical spirals, and log periodics. There is a vast and detailed body of literature on the subject of frequency-independent antennas that need not be reexamined here. One of the best references remains Victor Rumsey's classic book on the antennas he pioneered, now regrettably out of print [1]. Frequency-independent antennas are also a topic in most contemporary antenna textbooks.
One more-recent development in frequency-independent antennas is the "fractal" antenna like the Minkowski Island loop antenna of Figure 6.1. Fractal antennas are, in a sense, a generalization of the standard self-similar frequency-independent antenna. Some fractal geometries involve a looser sort of self-similarity called "self-affinity" in which a scaled replication of a particular geometric relation is skewed, distorted, or otherwise altered from one scale to another within the structure. Fractal antennas have...
