A 30-GHz Hexagonal Ferrite Phase Shifter

Highly-anisotropic hexaferrites, such as barium ferrite BaFe$_{12}$O$_{19}$ (BFO), are ideal for millimeter wave phase shifters due to a large ferromagnetic resonance frequency at low magnetic bias field $H$. It enables one to make millimeter-wave devices with compact magnetic systems. Here we discuss the design, fabrication and characterization of a BFO phase shifter. A microstrip line deposited on a ferrite substrate supports the propagation of electromagnetic wave, leading to a phase shift \textit{kb, }where $k$ is the wave number and $b$ is the length of the microstrip line. As $k$ is a function of the bias $H$, we obtain a differential phase shift with a change of $H$. A phase shifter consisting of a single crystal (7 x 7 x 0.5 mm$^{3})$ BFO and a 500 $\mu $m wide stripline was evaluated at 30 GHz. A differential phase shift of 30 deg. was measured for H=1.2 kOe. The measured value of the insertion loss was about 10 dB. -Work supported by a grant from the Delphi Automotive Corporation.