Fabrication and performance of ferrite phase shifters for millimeter frequencies

Ferrite devices for millimeter frequencies, 35 GHz to 94 GHz, are difficult to fabricate and have marginal performance. This paper discusses the design and arc plasma fabrication process for non-reciprocal ferrite phase shifters for millimeter frequencies. Design and fabrication techniques were developed for 35 GHz, prior to the initial fabrication of 94 GHz phase shifters. A lithium ferrite powder with a 4100 Gauss (4πMs) was used for arc plasma spraying the phase shifters, The treatment of the ferrite powder and its arc plasma spray characteristics are discussed. Device performance was evaluated with respect to insertion loss, bandwidth, and differential phase shift. Any imperfections in the fabrication of the ferrite phase shifters, such as cracks or poor ferrite dielectric fit, adversely affect their performance. Phase shifter design variations included: dielectric loading, placement of the switching wire, phase shifter height, and metalization techniques. Based on this work, it was possible to design and fabricate ferrite phase shifters with good performance at millimeter frequencies.