Substrate integrated waveguide isolators utilizing magnetic materials

Substrate integrated waveguides (SIW) are a recent transmission line technique that incorporates the high power handling capability of traditional machined waveguides with the ease of fabrication commonly found in planar transmission lines such as microstrip, coplanar waveguide, etc. With these planar waveguides different radio frequency (RF) devices such as filters, isolators and phase shifters can be constructed. One approach to these types of passive devices is through the appropriate use of magnetic materials.;The novelty of this work is two-fold. Incorporating a small sliver of ferrite the first tunable SIW isolator is introduced as a nominal, baseline device. This low-loss high-isolation device also takes advantage of traditional printed circuit board (PCB) fabrication techniques easily incorporated into a multilayered RF subsystem. The second important contribution of this work is demonstrating unique magnetic material properties to achieve novel performance enhancements.;In this thesis a series of SIW isolators using tunable, non-reciprocal magnetic materials are presented. A 20 mil thick SIW with micro strip transition elements was designed utilizing Rogers TMM-3 and 4003 substrate material using both standard PCB fabrication as well as a cheaper and faster milled circuit approach not previously demonstrated. Incorporating the non-reciprocal effects of magnetic materials a nominal, magnetization gradient and wideband isolator is demonstrated. The nominal isolator utilizes a single ferrite as a proof-of-concept device, as well as being the first ferrite isolator to be implemented in SIW. The magnetization gradient isolator utilizes a stack of ferrites to form a novel saturation magnetization gradient used to mitigate high order mode effects. The wideband isolator also uses a stacked ferrite configuration to create a tunable wideband response through tailored shape demagnetization terms. In addition to these three devices a fourth isolator with more efficient tapered ferrite transitions was studied for high-power effects and compared to the nominal configuration.;Before fabrication all devices were simulated and optimized using a tiered approach. The first is a coarse set of design specifications obtained through the application of simple magnetic material theory. Many fundamentals such as resonance frequency and shape anisotropy can be understood by these closed form equations and very quickly applied toward building practical devices. Further refinement and optimization was accomplished with Ansys' HFSS high-fidelity electromagnetic simulation software. Both simulated and measured results will be shown.