Ferrite Circulator Design-of-band Effect

As a nonreciprocal device, microwave ferrite circulators are widely used in the tranceiver systems to isolate the transceiver channels, with the purpose of protecting the circuits, because of its characteristics of simplex transmission. The isolation of the transceiver channels performs well in the work band of the microwave ferrite circulators. But very few researches are done on the characteristics out of its work band, especially, the parasitic passband and the tansmission characteristic in it. The main task of this paper is researching the out-band effects of the microwave ferrite circulators under high power microwave. At last, we drew some conclusions, which are useful for the protection of such instruments, by the analog design, processing, test and doing the research on the out-band effects of a pint-sized, double Y-junction microwave circulator at X-band.At the beginning, the thesis analyzes the electromagnetic transmission theory in ferrite circulation junction, then aided by full-wave electromagnetic simulation software, a Y-junction microstrip circulator has been designed and the simulation results showed isolation more than 20 dB,VSWR less than 1.2 and insertion loss less than 0.2dB in the frequency range of 6.8GHz~10.9GHz. Meanwhile, on the basis of the theory of Eigenvalue and simulation, an X-band double Y-junction microstrip circulator has been simulated and made. The measurement results showed greater 22dB isolation, lower 1.0dB insertion loss and less 1.2 VSWR in the frequency range of 10.9GHz~12.6 GHz.Through simulation and experiment test, there is a research on the out-band effects about actual production of circulator and market commercial circulators. According to the research, the circulation direction of the ferrite circulators may be opposite in the frequency near 3 f 0, that is to say, the isolation port of the ferrite circulator would turn into the transmission port, and the transmission port would turn into the isolation port. This weakness part of the circulator at its out-band shows that high power microwave at the out-band can be function in the transmission port with less attenuation, espessially at the T/R module, and bring the out-band damage effects. That is different from the general in-band effects, which is showed by the damage of the receiver link circuits caused by the high power microwave. The rule of this out-band characteristic is analyzed and summarized deeply.