Strontium Barium Ferrite From Bias Circulator Research

With the rapid development of modern microwave communication technology, the system integrated circuit is becoming more and more stringent requirements for microwave devices which goal for miniaturization, lightweight and integratability. Hexagonal ferrite material has high magnetocrystalline anisotropy field and remanence ratio, so that in the absence of external bias magnetic field circulators are self-biased. This will not only greatly reduce the weight and size of the device, but also make it possible to be integrated. Therefore, self-biased circulators based on hexagonal ferrite materials are of great significance.Firstly, based on the theory of traditional junction circulator, self-biased microstripe circulator was designed operating at22GHz. The simulation results showed that there was a non-reciprocal performance at22.6GHz with the insertion loss less than0.2dB, isolation and retum losses more than30dB. The self-biased circulator was prepared use the strontium and measured. The results showed that there is a clear circulation performance at22GHz which the insertion loss was2.8dB and corresponds to the maximum isolation nearly was50dB. But the minimum insertion loss was1.7dB at22.6GHz.Secondly, a minimization self-biased microstripe circulator with multiple open short lines impedance matching was designed and fabricated based on strontium hexaferrites which operated at28GHz. The simulation result showed that there was non-reciprocal performance with the insertion loss0.3dB, isolation and return loss more than35dB. The self-biased circulator was prepared use the strontium based on simulation result and showed that the size of device is smaller than the quarter-wavelength matching. The size of device was greater extent declined. The experiment results showed that the circulator worked at about29GHz with insertion loss of3.4dB and isolation of29.5dB, meanwhile VSWR was1.5between28.3GHz and29.3GHz.Again, in order to realize the broadband of self-biased circulator which its topology structure was setting beforehand based on the idea of stand wave ratio, direct optimization and real frequency data method. Then, according to different frequency points corresponding the integrated impedance value and combined with Smith chart in ADS software, finally a matching network infrastructure can be obtained. The simulation results showed that insertion loss was1.4dB, isolation and return loss were greater than10dB between28GHz and32GHz. It can be seen clearly that the device has a broadband feature. The broadband self-biased circulator was fabricated and measured, the results showed that isolation greater than15dB from28.8GHz to33.8GHz and the most isolation was25.1dB at29.8GHz, meanwhile the minimum insertion loss was5.6dB at29.6GHz.Finally, in order to meet the needs of integrated circuit development, an integrated self-biased microstrip circulator was designed at X band which based on the integration of perturbation theory. An integrated circulator which was fabricated using with alumina and strontium ferrite and was measured. The measurement results showed that there was lOdB non-reciprocal performance at11.4GHz. Among which minimum insertion loss was5.7dB, the maximum isolation was15.5dB and the return loss was28.1dB.