Investigations On Magnetic-free Nonreciprocal Devices

Traditional non-reciprocal devices such as circulators and isolators are widely used to decouple and isolate the transmitting and receiving of RF front end,to reduce the self-interference of the same frequency.It is constructed by non-reciprocal magnetic materials such as ferrite.Non-reciprocal characteristics of ferrite are realized by Faraday rotation effect,which is generated by magnetic field bias.However,the preparation process of ferrite and other magnetic materials is difficult to compatible with the traditional silicon substrate integration process.So,it is hard to realize integration and miniaturization of nonreciprocal devices.Besides,the preparation process has high cost and pollution.Ferrite devices often occupy large volume and mass,which used as discrete components in RF system.Therefore,it has great potential to develop magnetic-free non-reciprocal devices to realize integration and miniaturization of non-reciprocal devices.This paper studied magnetic-free non-reciprocity devices from the perspective of time-varying transmission line.It controls the value of distributed parameters in the equivalent model of the transmission line using time modulation,thus breaking the symmetry of time inversion and further obtaining non-reciprocity characteristics.Therefore,the research contents of this paper are list as follows:Magnetic-free non-reciprocal phase shift circuits have been studied.The time-varying switch is used to control the propagation process of signals in the transmission line to constitute the non-reciprocal phase shift circuits.Research work has been done,and a magnetic-free balanced gyrator(MFBG)has been made to verify the theory.What is more,a magnetic-free differential balanced gyrator(MFDBG)has been studied based on the balanced gyrator.Phase difference between the two opposite directions is 180 degrees with frequency independent.A prototype has been made to verify the theory.At the same time,the insertion loss caused by the delay error of the transmission line and the duty cycle error of the control signal in the MFDBG is discussed and analyzed.Magnetic-free isolators have been studied.Three magnetic-free non-reciprocal amplitude structures are designed based on the switch-controlled time-varying transmission line(TVTL).Using the resistor absorption switch,an magnetic-free ultra-broadband dissipative isolator(MFUDI)can be realized,which can absorb the reverse transmission signals in wideband range,while the forward transmission signals have small attenuation.Besides,a magnetic-free frequency conversion isolator(MFFCI)is studied.The reverse transmission signals in the isolator are modulated by the switch control signal and can converse to other frequencies to realize isolation.The isolation and bandwidth limitation of the structure in the frequency conversion isolator is further discussed and analyzed in this paper.In addition,two magnetic-free isolators are designed in this paper:1.Based on the MFUDI structure,a reconfigurable magnetic-free broadband isolator is designed,which is called magnetic-free single-ended transmission isolator(MFSTI).The isolation direction of the isolator can be changed by changing the phase relationship between the control signals.Compare to the MFUDI,the MFSTI has a higher isolation.2.In order to improve the power capacity and enhance the suppression of the common mode signal by the structure.A magnetic-free differential transmission isolator(MFDTI)is designed in this paper,which combined four Wilkinson power dividers.Isolation of the reverse signal are realized by the coherent cancellation of differential signals.Combining a reciprocal transmission line segment with MFBG,a three-port circulator can be constructed.Coherent superposition of signals at ports is used to realize the narrow-band circulator.Based on the broadband magnetic-free isolator and MFDBG,a three-port and a four-port broadband magnetic-free circulator are realized respectively,which were called magnetic-free single-ended transmission circulator(MFSTC).Finally,it is extended theoretically to the N-port magnetic-free circulator.Due to the limited power capacity and limited anti-interference ability of the above structures,this paper designs an anti-interference,high power capacity magnetic-free circulator,which is called magnetic-free differential transmission circulator(MFDTC).The MFDTC can be converted between circulator and isolator by changing switch control signal.The time-varying transmission line theory has provided some new ways to design non-reciprocal devices.Without magnetic material,nonreciprocal devices can be integrated and miniatured more easily.