| Harold Wheeler, in his classic 1947 papers, created the fi eld of electrically small antennas. This fi eld has long been important for frequencies below roughly 1 GHz, where a half-wavelength is about 6 inches. These electrically small antennas have characteristics in common that limit performance: low radiation resistance, high reactance, low effi ciency, narrow bandwidth, and increased loss in the matching network. Most of these limitations are shared by two other classes of antennas: superdirective antennas and superconducting antennas. This book is divided into three interrelated chapters: Chapter 1 on electrically small antennas, Chapter 2 on superdirective antennas, and Chapter 3 on superconducting antennas. Each chapter includes extensive references and an author list. An overall subject index is provided at the end of the book. We antenna engineers have done what is possible by rearranging the wires; future signifi cant advances will come through use of new low-loss magnetic materials and through use of circuits to compensate for impedance deficiencies. Both areas are addressed.
Many engineers interested in these topics have not had the benefi t of early papers on these three subject areas. This book aims to be a primer on what has been investigated and what works. Over the years many ideas on improving electrically small antennas have appeared. These are discussed under three categories: designs that work, clever physics but bad numbers, and pathological antennas. In retrospect, the simplest antennas are the best: dipoles with or without fatness or loading; patches with appropriate substrates. There are no wideband electrically small antennas, unless effi ciency is sacrifi ced for bandwidth. The relatively new fi eld of Non-Foster circuits may change this situation. |
