Design And Research Of Flexible Microwave Filter With Low Deformation Sensitivity

In recent years,wearable communication devices have penetrated into all aspects of economic development and social life.Flexible electronic technology for flexible wearable devices has attracted wide attention in the field of microwave and has developed rapidly.The design of high stability conformal antenna,flexible transmission line,flexible filter and other microwave devices becomes more and more urgent,and the performance requirements of flexible microwave filter are also higher and higher.The existing flexible filter design only focuses on how to process the filter on a thinner polymer or flexible organic material substrate to achieve device flexibility,but ignores the traditional filter structure changes in bending,stretching and other deformation states and the resulting deterioration of filter performance Research on change is relatively scarce.In addition,the traditional conductor material is easy to fatigue and irrecoverable,which limits the traditional flexible filter to be more suitable for the application scenarios of stretching,folding and high use frequency of wearable devices.Aiming at the above two problems,this paper studies and verifies two low deformation sensitivity optimization methods based on parallel coupled microstrip structure,designs a new flexible hairpin structure filter and a defect ground structure ultra wideband flexible filter,and realizes the bending,stretching and torsion characteristics of the two flexible filters by using liquid metal processing.The main work of this paper is as follows:(1)Two optimization methods of low deformation sensitivity based on parallel coupled microstrip structure filter(etching periodic square groove and loading open circuit branch)are proposed,and two flexible band-pass filters with center frequency of 9.5GHz are verified to effectively suppress the center frequency shift caused by bending.In this paper,the deformation characteristics of coupled microstrip lines are studied and analyzed.The influence of bending in different directions and curvatures on the performance of the filter is analyzed from the perspectives of electric field distribution after bending,characteristic impedance of odd and even models,and second harmonic.By etching periodic patterns and loading open branches,the transmission path of odd mode is extended,and the problem of increasing phase velocity difference caused by bending is balanced.The experimental results show that the optimized flexible filter can reduce the center frequency offset more than 66%in different bending states compared with the straight state.(2)A new type of flexible hairpin structure with low deformation sensitivity is designed,which uses liquid metal processing to achieve the high flexibility of extensibility and self recovery.This paper studies and analyzes the performance changes of the basic hairpin structure filter after bending,analyzes the influencing factors brought by bending in the design process of the filter,optimizes the coupling coefficient between the hairpin resonance units caused by bending,and summarizes the design rules under the deformation state of the hairpin structure.The simulation results show that the structure can effectively reduce the degradation of insertion loss caused by bending and more than 90%of the center frequency shift.(3)A novel ultra wideband(UWB)liquid metal filter with low deformation sensitivity is designed.Based on the parallel coupled filter,the flexible optimization effect of the loaded defected ground structure is verified.The measured results show that the frequency offset caused by bending is effectively reduced.The equivalent circuit change of defected ground structure caused by bending is analyzed.The high frequency attenuation pole is introduced to suppress the high frequency band frequency offset caused by the bending of microstrip patch structure.The simulation results show that the flexible structure filter has low deformation sensitivity.At the same time,the liquid metal filter was fabricated by PDMS.The filter proposed in this paper has the advantages of simple structure,stable deformation performance and high ductility,covering WiFi,Bluetooth frequency band of wearable devices and ultra wideband technology frequency band approved by FCC Committee,and can be widely used in RF/microwave wearable communication devices.