Microwave Active Circulator

As essential devices, microwave circulators are widely used as importantcomponents for communications and radar transceivers. The previous generations ofcirculators are composed of ferrite whose properties are realized by adding bias H fieldto it, which leads to the huge size and heavy weight of such devices as well asinconvenience of their integration with MMIC technology. Active circulators offer analternative approach to ferrite circulators with potential advantages in small size, lightweight, and compatibility with monolithic-microwave-circuit (MMIC) technology.This paper aims to present the theory and method for designing active circulators.In order to achieve that, this paper begins with an analysis of the fundamental principlesof several types of active circulators, from which the typical divider/combine kind,based on a detailed analysis of noise figure, is improved for realizing the microwaveactive circulators.On the basis of theoretical analysis and with the help of EDA software,the active circulators are modeled and simulated.An active quasi-circulator using HEMT was researched and designed finally. Thecirculator,operate at C band (f0=5.8GHz).The result is very close to the simulated one:within 5.4GHz～6GHz, the gain of the device are larger than 1dB, isolation greater than18dB, and noise figure about 1.5dB. The gain of the active circulators is better than thatof the C-band monolithic active circulator reported in domestic magazines, while theisolation and noise of the active circulators are superior to that Of the MMIC circulatorat the same band reported abroad.