Research On Microwave Flexible Filter Based On Microstrip Structure

With the rapid development of the wireless communication system,the performance of the microstrip microwave filter is more and more high,which promotes the development of the high performance,low loss and miniaturized microwave flexible microstrip filter.Compared with the traditional rigid microstrip filter,the flexible filter has the advantages of bending,folding,extension and light weight,etc.,owing to the flexible substrate,and it can be realized by conventional lithography process,has low cost,simple manufacturing process and high efficient.The characteristics of the organisms are soft,bendable,and the traditional rigid filter does not apply in the biomedical field.However,the flexible filter will be easier match with the curved surface of the organism due to the advantages of bending easily.It will have large potential application value in biomedical detection and treatment.This subject aims at optimising the design of resonant circuit to bring a constant or minor change of the flexible filter's performance in the case of different bending,extending the application of microstrip filter.In this paper,the design of the miniaturized microstrip flexible filter choosing Rogers 3850 as the substrate.The substrate material is Liquid Crystal Polymer,which has low dielectric loss,broadband stability,low moisture absorption and thermal expansion coefficient,etc.in the radio frequency,microwave and millimeter wave(up to 110GHz).Four compact different types microwave microstrip filters are developed,stepped impedance structure,the open-circuit and short-circuit stub structure,0?pseudo interdigital structure and defect structure.The 0?pseudo interdigital structure is achieved by the traditional interdigital structure to remove short-circuit connection(via hole).The connection of the two resonance units can also form an electric short-circuit at the center frequency so as not to change the voltage and the current distribution,and is easy to realize the small size and the plane manufacture.The structure of spiral defect increases the surface area of the ground to increases the equivalent inductance,and decreases the resonant frequency so that the filter size is smaller.The method of flexible modeling in 3D full wave electromagnetic simulation software is studied,using the method of Wrap Sheet to complete the simulation and the performance of the microwave flexible filter under different bending radius is analysed in detail.TheS-parameters show that the flexible filter is not sensitive to the structural bending compared with flat case.Moreover,the performance of the flexible filter are optimized under a specific bending condition,such as: return loss(RL)and insertion loss(AL).And the physical test is carried out to verify the correctness of the analysis results,which provides a new idea for us to realize miniaturized microstrip filter with high performance.Compared with the traditional rigid microstrip filter,the flexible filter has advantages of low cost,small size,easy to match with biological curved surfaces and so on.There have a very wide application prospect in the miniaturized microwave circuit,and wearable electronic devices with conformal characteristics.The ultra wide band(3.1-10.6GHz)flexible bandpass filter has the advantages of low loss and high stopband rejection,and the flexible bandpass filter which is work in the WLAN band of 5GHz will alleviate the congestion of traditional communication 2.4GHz channel.