The development and current status of microwave ferrite technology is reviewed in this paper. An introduction to the physics and fundamentals of key ferrite devices is provided, followed by a historical account of the development of ferrimagnetic spinel and garnet (YIG) materials. Key ferrite components, i.e., circulators and isolators, phase shifters, tunable filters, and nonlinear devices are also discussed separately.

Magnetostatic wave propagation at microwave frequencies through a periodic structure formed by selectively etching the surface of an epitaxial yttrium iron garnet (YIG) film is reported. Experimental insertion loss data obtained in the 2–4-GHz range from a structure comprising 20 grooves each 1 μm deep and 30 μm wide, and each separated by 120 μm, formed in a 9-μm-thick YIG film are in good agreement with theory based on repetitively mismatched transmission lines.

A top-gated carbon nanotube (CNT) field-effect transistor (FET) was fabricated on a quartz substrate. We used a novel measurement approach and demonstrated for the first time frequency-independent performance of a CNT FET for frequencies as high as 23GHz. This observed maximum operating frequency represents a significant breakthrough in the realization of carbon nanotube-based electronics for high frequency applications.

The authors consider the suitability of carbon nanotubes for use in analog rf amplifiers, where the linearity of the device is critical. They show that in the limit of large electrostatic gate-channel capacitance, their theory predicts that an Ohmically contacted, ballistic carbon-nanotube-based field-effect transistor is inherently linear. While they have not achieved this limit in their experimental work, they compare the theory to experiment in the limit of small electrostatic gate-channel capacitance and find excellent agreement at virtually all bias conditions.