Design Simulation and Analysis of X Band Microstrip Circulator

Abstract

Microwave circulator is an important microwave ferrite device which is widely used in wireless transceivers. Many approaches are found for the designing of stripline and waveguide circulators which includes analysis of stripline circulator in terms of scattering matrix, broad banding of above resonance circulator, phenomenological description in terms of rotating modes, different topologies regarding waveguide cir- culator configuration and many more. No universal equations or approach exist for designing of microstrip circulator. This thesis presents design, simulation and analysis of X-band microstrip junction circulator. Major application of microstrip junction circulator presented here is as duplexer in RADAR. Other application includes providing isolation to source or load, multiplexing, phase shifting and many more. The circulator designed here is centered at 9.6 GHz with 800 MHz bandwidth. According to the specification, isolation of more than 20 dB and insertion loss less than 0.4 dB is required which is at par with industrial standards. Yttrium iron garnet (YIG) is used as ferrite material. Here, the design equations given by Fay and Comstock are followed and many prototypes are simulated using CST Microwave Studio. As an important aspect of this thesis, first ferrite is selected from available choices based on the comparative study of its properties. Ferrite radius is determined theo- retically and practically. Two types of electrical designs are prepared from which one prototype is designed with two types of magnetic circuits. Obtained S parameters are compared, which are better than the main objective.