Iron based microstrip phase shifter; optimization of phase shift

摘要

A microwave phase shifter is a device used to introduce phase change in a propagating electromagnetic wave in a waveguide. A series of microstrip transmission lines, with an iron film of 300 nm thickness placed at various places inside a SiO_2 dielectric layer, was fabricated and tested as phase shifters based on ferromagnetic resonance principle. It is observed that the differential phase shift obeys a Sin2 - law (derived from perturbation theory) given by; Δβ ∝ Sin~2(πx/h). Here, x is the distance of Fe film inside SiO_2 dielectric from the Cu conductors, h is the height of SiO_2 dielectric. This give Δβ as minimum when Fe film is at the two edges of the dielectric and maximum when Fe is at the center of the dielectric. The differential phase shift varies as high as 350° at resonance (20 GHz), when Fe is at the middle of the dielectric. For high (at 25 GHz) and low (at 8 GHz) frequency operation, far above and far below resonance, the differential phase shift is ～125° and 250° when Fe at middle of the dielectric. This trend is same for absorption - it is a maximum when Fe at the middle.