Research And Implementation Of Flexible Microwave Filter

With the rapid development of flexible electronic technology,flexible electronic devices designed and manufactured by relevant technologies are emerging.At the same time,the manufacture of flexible electronic devices is also promoting the research and development of flexible wireless communication system.Wireless communication system is composed of many kinds of microwave RF devices.As one of the most critical components in the wireless communication system,the flexible implement of microwave filter is very important to the realization of flexible wireless communication system,and it has great research value.The purpose of this paper is to design a flexible microwave filter with high selectivity and wide stopband,so that the microwave filter has good filtering performance and deformable ability.At the same time,the structure of the flexible microwave filter is optimized,so that the change of transmission characteristics of the filter can be suppressed in the deformation state,and it has good anti-deformation sensitivity.The main works and innovations of this paper consist of:1)Using transversal signal-interaction concept,this paper designs two flexible bandpass filters.One is based on shorted stubs and shorted coupled line,the other is based on enhanced coupled line.Due to the effect of interference of the two path signals,these two filters have transmission zeros which near the passband,make the filters have good selectivity.The first filter’s stopband suppression range is extended through the cascade harmonic suppression unit.The center frequency of the filter is 4.21 GHz,the 3-dB fractional bandwidth of 22%,the selectivity of the lower band is 45dB/GHz,and 63dB/GHz for the upper band.In the second filter,defected ground structure is used to enhance the coupling strength of coupled line.The center frequency of the filter is 3.98GHz,the 3-dB fractional bandwidth of 20%,the selectivity of the lower band is 61.5dB/GHz,and 43dB/GHz for the upper band.The performances of these two filters almost do not change under bending state in measurement,have great anti-deformation sensitivity.2)The changes of transmission characteristics of microstrip line in bending state is analyzed,and the optimized design of flexible microstrip line based on defected ground structure is proposed.This optimized design method is applied to the stepped impedance lowpass filter,and propose the design of flexible stepped impedance lowpass filter based on the defected ground structure.After adding the defected ground structure,the cutoff frequency offset of the flexible stepped impedance lowpass filter under bending state is reduced by 31%～83%in simulation,and the cutoff frequency and other parameters of the filter under bending state almost do not change in measurement,which indicates that the filter has good anti-deformation sensitivity.The performances of the flexible bandpass filters designed in this paper almost do not change under bending state in measurement,which prove these filters have good anti-deformation sensitivity.These two kinds flexible filters can be used in the flexible wireless communication system.The optimized design method of flexible microstrip line based on defected ground structure proposed in this paper has been applied to the flexible stepped impedance filter to prove its effectiveness.It can be applied to the optimized design of flexible microwave filter based on microstrip line with large frequency offset in bending state.