Passive Nonreciprocal HF Helicon Devices

Ferrite isolators and circulators are well known at microwave frequencies but are low-frequency limited and cannot be used in the HF region (below 100 MHz). A different approach to the basic nonreciprocal mechanism is reported here. This approach makes use of solid-state plasma waves, so-called helicon waves, that are nonreciprocal by their nature. Isolators using these helicon waves have been built in the 5-to 15-MHz range with great success and a helicon circulator has been demonstrated for the first time. This paper describes the mechanism by which these devices work and discusses their results. It is pointed out that in addition to helicon isolators and circulators, many other interesting and useful devices using helicon waves are possible.