Nonreciprocity Mechanism And Manipulation Optimization Of Bulk Acoustic Wave Circulator

Circulator is a nonreciprocal device that supports unidirectional circular transmission of signals between ports,and has been widely used in duplex communication fields such as radars and base stations.However,most of the commercial circulators are ferrite circulators which are realized by applying a constant DC magnetic field to the ferromagnetic medium.They are difficult to be used in miniaturized communication devices due to their large volume and high cost,especially the incompatibility between magnetic materials and integrated circuit(IC)manufacturing process.therefore,the research of magnet-less circulator has vital practical significance.The bulk acoustic wave(BAW)circulator as a new type of magnet-less circulator,which is composed of bulk acoustic wave resonator chip and spatiotemporal modulation(STM)circuit connected in a Y topology.First,the non-reciprocal mechanism of BAW circulator is studied;Then,the influence of modulation parameters on the scattering properties of BAW circulator is analyzed by theoretical calculation and circuit simulation,so as to determine the optimal manipulation conditions;Next,the above analysis is verified by physical test;Finally,the differential manipulation is used to optimize the performance of the circulator.The specific research work and results are as follows:(1)Based on the time-domain coupled mode theory,the non-reciprocal mechanism of the BAW circulator is studied,and the analytical model of BAW circulator is derived,and the influence of modulation parameters on the scattering properties of BAW circulator is analyzed theoretically.A case of BAW circulator is presented to demonstrate the analysis process.Theoretical calculation shows that under the optimal manipulation conditions,the modulation frequency is 3 MHz and the modulation amplitude is 12 MHz.At this time,the insertion loss,isolation and return loss of BAW circulator are 2 d B,16 d B and 10 d B respectively.(2)Circuit model establishment and simulation analysis of BAW circulator.First,the circuit simulation model of BAW circulator is established;Then,the scattering properties of BAW circulator under different manipulation conditions are simulated by using hybrid timefrequency domain harmonic balance(HB)method.The simulation results show that under the optimal manipulation conditions,the modulation frequency is 3 MHz and the amplitude of modulation voltage is 5 V.At this time,the insertion loss,isolation and return loss of BAW circulator are 3.6 d B,14 d B and 10 d B respectively.(3)A sample of BAW circulator was fabricated and tested.According to the value and model of each component determined in the circuit model,the PCB design,device assembly,test platform construction and final performance test of BAW circulator are completed.When the modulation frequency is 3 MHz and the amplitude of modulation voltage is 5 V,the measured results show that the insertion loss,isolation and return loss of BAW circulator are7.6 d B,14 d B and 5 d B respectively.(4)The BAW circulator with differential manipulation is used for optimization the performance of the circulator.HB simulation is used to analyze the differential BAW circulator.The final simulation results show that the insertion loss of differential BAW circulator is 1.8d B,the isolation is 14 d B,and the return loss is 20 d B.The performance of differential BAW circulator is obviously better than that of single ended BAW circulator.