Research And Design Of Active Circulator

The circulator is a RF device with three terminal ports,it passes signals incident on one port to the next port in either a clockwise or counter-clockwise direction,and dose not allow signals to pass in the opposite direction.The traditional circulator is usually made of ferrite materials which cannot meet low cost,and be inconvenient to integrate with MMIC.In order to solve this problem,an active circulator based on transistors emerges.It can save space and cost,and easy to achieve integration,so it has broad prospects for development.The main contents are as follows:1.Firstly introduced the principle of nonreciprocal phase shifter and analyzed the implementation of active circulator based on it.The power and noise of this active circulator are studied and analyzed and it lays a theoretical foundation for the optimization of the active circulator.The limitation of the active circulator is pointed out.The active circulator designed works in the frequency of 1.8GHz and forward transfer loss during ports is 2dB.It reached the isolation degree of 30 dB.2.Based on the idea of leakage cancellation,a qusi-circulator is designed.A differential amplifier is used to realize the power distribution,so as to introduce an equal amplitude inverse-phase transmitting signal to offset the leakage signal.The analysis of its power and noise performance shows that it has better power output and noise performance.The implemented active quasi-circulator has a isolation degree of more than 20 dB within the range of 0.2-2.5GHz frequency band.3.Based on the cancellation principle of active quasi-circulator,a solution of integrating active quasi-circulator with antenna is proposed.Dual-Circularly Polarized Antenna is used to cancel the leakage signals,so as to solve the problem that the leakage signals cannot be completely canceled due to the mismatch of antennas.The experimental results show that the isolation of the active circulator can reach more than 46 dB.