Modelling partially magnetised Y-junction circulator

Y-junction circulators are widely used in many wireless communication systems to route signals and protect power source. Typical applications such as duplexers and isolators are found numerously for example in base stations in mobile phone and satellite systems. The principal operation, circulation of incident signal, becomes possible because of the ferrite material placed at the centre of Y-junction circulator. Its operation and design is mainly determined by considering the resonant characteristics of ferrite material as a function of an applied magnetic field. The normal resonant loss curve of ferrite material with respect to the biasing field is shown in the Fig.1 [1]. It can be seen from there that there are two loss regions and engineers try to avoid these regions in the design of Y-junction circulator. Normally operating regions either below or above main resonance are selected. However it has often been necessary to consider partially magnetised regions to optimally design circulators used for control devices. This situation implies that the ferrite devices need to be run in the region below the low field loss region, which again means that, after careful selection, the ferrite should be magnetised very weakly to avoid the low field loss as can be confirmed from the Fig.1.