PROJECTS
(click to view)
Low-cost Nonplanar Microstrip-line
Ferrite Phase
Shifter
Utilizing Circular Polarization
RORY
SORENSEN & MAGDY ISKANDER
PROJECT
DESCRIPTION, MOTIVATION, & RELATED WORK
Microwave ferrite phase shifters are primarily used in phased-array antenna systems to electronically steer the antenna beam. Because a typical phased-array antenna system consists of thousands of radiating elements, consequently, thousands of phase shifters are also needed. Therefore, low-cost, compact phase shifters are required that can provide the full 360° range of phase shift. Present-day ferrite phase shifters maximize phase shift over a given distance by producing circularly polarized microwaves to interact with the magnetic dipole moments in the biased ferrite material. This is typically done by placing a longitudinally (i.e., in the direction of propagation) biased ferrite rod in the center of a waveguide. Although this technique produces the desired phase shift, it is costly to manufacture because the cross-section of the structure is a fraction of the operating wavelength.
 |
Fig. 1. Geometry of the ferrite phase shifter. The ferrite rod is magnetically biased in the direction of propagation. The nonplanar orientation of the three parallel microstrip lines aids in the creation of circularly polarized waves in the ferrite rod embedded in the substrate. |
|
In 1993 Lee and Strahan at Hughes Aircraft Company (now Raytheon) proposed a low-cost alternative solution to the current ferrite phase shifter designs, namely, a planar ferrite phase shifter based on printed-circuit technology that could theoretically produce circularly polarized waves in the ferrite substrate. They obtained a U.S. patent (5,223,808) for their invention. However, at the time there were no microwave simulators capable of analyzing their invention. Last year at the University of Hawaii, Raytheon's patented ferrite phase shifter was modeled (with their permission) using Ansoft's High Frequency Structure Simulator (HFSS) software—now capable of simulating the effect of an applied magnetic bias on a B-H nonlinear (ferrite) material. It was found that the horizontal electric-field component was much weaker than the vertical component, resulting in elliptical polarization rather than circular polarization. In order to transform the elliptically polarized wave into a circularly polarized wave, the geometry of the Raytheon phase shifter needs to be modified to produce a nonplanar ferrite phase shifter—the focus of this project. |
MILESTONES & FUTURE
WORK
During 2003 a low-cost nonplanar microwave ferrite phase shifter, as seen in Fig. 1, was designed and simulated at 3 GHz at the University of Hawaii. The amount of phase shift between the input and output ports is determined by the strength of the applied bias magnetic field (e.g., resulting from a current-carrying coil wrapped around the structure). A microstrip three-way power divider (shown in Fig. 2) was designed to feed the microstrip lines with different magnitudes and phases.
|
