Advancements at the Lower End: Advances in HF, VHF, and UHF Systems and Technology

In the March 2002 issue of IEEE Transactions on Microwave Theory and Techniques (T-MTT), Frederick Raab, chair and founder of the highfrequency (HF), very high frequency (VHF), ultrahigh frequency (UHF) technology technical committee of the IEEE Microwave Theory and Techniques Society (Technical Committee 17), organized an extensive overview paper "HF, VHF, and UHF Systems and Technology" [1]. The paper started with the early-20th-century notion that frequencies above approximately 1.5 MHz (200 m and down) were useless for communications, a fact soon discovered to be incorrect as experimenters and amateur radio enthusiasts showed the utility of the higher frequencies. The paper reviewed HF through UHF communication techniques and technologies, various propagation modes, and a number of systems and applications below 1,000 MHz. There have been many advances in this frequency range in the intervening years, some of them quite striking, as well as new applications and other applications not mentioned in the paper; updating the paper on HF, VHF, and UHF technology is the major focus of this article. In addition to updates on some of the material in the original paper, new technologies and/or a better understanding of electromagnetic (EM) behavior have occurred, and these are included in this article.