Design of a Stripline based Isolator and Circulator at Ultra High Frequency band

Abstract

Ferrite circulator and isolator are being used immensely in the microwave industry and are being exploited extensively because of their unmatched properties and capabilities. In simple terms, a circulator is a ferrite loaded symmetrical junction consisting of a transmission line for signal transfer for one port to another. This transmission line could be a strip-line or even a micro-strip line depending upon the requirement. The circulator has a special property of transferring power from the incident port to the immediate port and isolating all the other ports. The non-reciprocal characteristics of ferrite under the influence of magnetic bias fields makes this action possible. An isolator can be thought of as the terminated equivalent of circulator. Theoretically, the circulator and the isolator can have any number of ports but practically three and four port circulators are the most popular. This thesis presents the method for designing a strip-line circulator and an isolator. The main modelling factors considered are the radius, the type of the magnetic field, the biasing configurations and the value of the dielectric constant. The radius of the ferrite disk and the biasing field required for the working are calculated and dependency of the various factors on frequency and other quantities involved is also stated.