Research And Implementation Of Flexible Microwave Filter

In recent years,the rapid development of flexible electronic technology has attracted the attention of many research institutions and research enterprises.Compared with traditional rigid circuits,flexible electronic devices have the characteristics of light weight,bendability,folding,extensibility,and easy to fit with complex surfaces,so they have broad application prospects in many aspects.RF filter is an important device in RF transceiver system,and its performance affects the performance of the entire communication system.There are various types of RF filters,among which microstrip filters are favored for their compact physical structure,lightweight volume,ease of assembly with other components,and simple manufacturing processes,and have been widely used in various fields.1)The purpose of this paper is to design a miniaturized flexible filter with good passband performance and high out-of-band rejection performance.The main research contents are as follows:A flexible ultra-wideband bandpass filter is designed based on the cascaded matching of low-pass structure and periodic bandpass structure.Based on this,a parallel resonant circuit is constructed using an interdigital coupling structure and an etched defective ground loop.The passband range of the filter is 3.13-11 GHz,the insertion loss in the passband is less than 1dB,and the return loss is better than 15dB.And because the parallel resonant circuit generates transmission zeros out of band,the out of band suppression level is improved,and the insertion loss out of band suppression characteristic reaches 39.5dB at 17GHz.The performance simulation and test results of the filter in both straight and bent states show that the passband in and out of band performance of the filter in bent state is basically consistent with that in straight state.2)A dual-band bandpass filter was designed based on a T-shaped resonator.In response to the weak coupling strength caused by a thin substrate,a pseudo interdigital structure was used to enhance the internal coupling strength of the T-shaped resonator and reduce the overall filter volume.At the same time,the zero-degree feeding structure is adopted,and the transmission zero point is added outside the passband to improve the out of band suppression level of the filter.The center frequency of the second frequency band of the filter can be adjusted independently by adjusting the length of the open circuit branch line of the resonator.The center frequency of the filter is 2.28GHz/4.46GHz,the insertion loss in the passband is less than 2.11dB,and the return loss is better than 11dB/13dB.The out of band suppression characteristics of the filter at 3.18GHz and 5.14GHz are 45.5dB and 38.5dB respectively,with good out of band rejection performance.The performance simulation and test results of the filter in both straight and bent states show that the passband in and out of band performance of the filter in bent state is basically consistent with that in straight state.3)A dual-band bandpass filter is designed based on microstrip transmission lines,open circuit stubs,and coupled microstrip lines.Each transmission line is cascaded.Each transmission line is cascaded in the circuit.By calculating the overall network parameter matrix of the circuit,the frequency position of the transmission zeros and poles can be determined from the electrical length and impedance of the corresponding transmission line.The test results indicate that:the center frequency of the filter is 2.32 GHz/5.23 GHz,and the insertion loss in the passband is less than 1.5dB.The insertion loss characteristics of the filter at 3.71 GHz and 6.22GHz are 81.2dB and 93.5dB respectively,with good out of band rejection performance.The performance simulation and test results of the filter in both straight and bent states show that the passband in and out of band performance of the filter in bent state is basically consistent with that in straight state.The flexible microstrip filter designed in this article is not sensitive to bending deformation and has broad application prospects in fields such as flexible wireless communication systems,wearable devices,and electronic skins.