Microstrip Junction Circulator Design And Simulation Study

Ferrite circulator is an important component in contemporary communication systems. With the development of communication technologies, microstrip circulator has become a major object of study because of the small size, ease of integration, etc. Therefore it is important to carry out design and research of microstrip circulator.In this paper, first of all, the circulator's basic working principle was studied, and on this basis, the circulator design methods and processes also were studied. Then,we designed of an microstrip junction circulator that the center frequency is 5GHz based on this method, and simulated and optimized it using HFSS software. The results show that, the circulator has a good circulation performance between 3.0 and 4.7 GHz. Its isolation is more than 18 dB, insertion loss less than 1 dB. Then we used the double Y junction circulator structure to optimize the structure. The results showed that the double Y structure circulator's bandwidth increased significantly, which showed a good performance at the frequency range of 3.5-9.5 GHz. The minimum insertion loss was 0.06 dB, and the isolation and return loss were greater than 28 dB. Circulator structure parameters are identified as: center disc radius is 2.75 mm, conduction band line width is 1.55 mm, ferrite thickness is 2 mm, Based on the circulator structure which has been designed and optimized, we prepared a sample circulator using lithography processes. Test results showed that at the frequency range of 2.5-5.5GHz, the smallest insertion loss is less than 1.1 dB, the maximum reverse isolation reached 22 dB.Secondly, we explored to design and produce small-scale integration of self-biased circulator using a "thick film ferrite / dielectric substrate" structure. In this work, we designed and simulated an integrated circulator, and studied microwave transmission characteristics of the integrated circulator structure and material parameters on the properties of circulation. The results show that the integrated circulator performance is not only impacted by the thickness of ferrites, but also by the relative thickness of ferrite and dielectric substrates. The microwave transmission characteristics of circulator is closely related to the saturation magnetization of ferrite materials. When the radius of the circulator center conduction disc and conduction line size were changed in the range of 5% of the designed size, integrated circulator continues to show better performance. Finally, through optimization the integration circulator structure parameters are identified as: center disc radius is 0.97 mm, conduction band line width is 0.6 mm, ferrite thickness is 0.1 mm, and the substrate thickness is 0.2 mm using the alumina. We prepared "BaFe12O19/Al2O3" integrated circulator using lithography and tested its microwave transmission characteristics using Agilent 8720 network analyzer. Experimental results show that the circulator's insertion loss is 8.5 dB, and the isolation loss is 12.5 dB at 27 GHz, which show an obvious circulation.