Research On Reconfigurable Surface Acoustic Wave Resonator Based Filters

With the rapid development of information industry,the communication systems gradually become multi-functional and highly integrated.As one of the significant components of the communication system,the reconfigurable filter can work in the multi-frequency and multi-mode electromagnetic environment.It has gradually become a hot spot of researchers due to its multiple functions,compact structure and low cost.Surface acoustic wave resonators are widely used in the design of radio frequency filters due to their compact size,high frequency selectivity and low insertion loss in the ultra-high frequency band.In this paper,the design of single-band and multi-band bandpass-to-bandstop filter,bandwidth tunable bandstop filter and bandwidth tunable bandpass filter are reported.They are based on the hybrid-technology design approach in which surface-acoustic-wave(SAW)resonators are combined with microstrip or lumped-elements.The main contents are as follows:Firstly,we propose a class of bandpass-to-bandstop reconfigurable SAW filters whose transformation is realized by adjusting the PIN diodes to select the transmission path.The responses of loading the ground inductor on the SAW resonator in different ways are opposite.Based on this principle,a microstrip dual-path structure and a lumped single-path structure that employs PIN diode to control the the on-off between source and load are used to realize the single-band and dual-band bandpass-to-bandstop reconfigurable filters.The two filters operate in the UHF frequency band,and they have the characteristics of compact structure and high in-band isolation.Secondly,based on the SAW symmetric ?-type bandstop structure,a single-band bandwidth tunable bandstop to zeros tunable bandpass filter and a dual-band bandwidth tunable bandstop filters are proposed in this paper.Variable elements are introduced into the two symmetrical ?-type fixed response notch structures.The odd-even mode analysis method is used to illustrate the influence of variable element values on the positions of transmission poles and zeros.It is found that various values of variable elements can affect the bandwidth and transmission response switching through transmission poles reallocation.The measured results show that the proposed two filters have the characteristics of compact structure,enhanced bandwidth adjustment ratio,and quick adjusting methods.Finally,based on the method of variable capacitors or inductors loading surface acoustic wave resonators,single and multi-band bandwidth tunable bandpass filters are proposed.The concept of tuning resonance and anti-resonance frequency is introduced into the resonator series inductor bandpass structure,that is,the parallel and series variable capacitors are loaded simultaneously.By analyzing the influence of variable capacitors on transmission zeros and poles,single and dual-band bandwidth tunable bandpass filters can be achieved.In order to realize the independent adjustment of the bandwidths,a transversal hybrid module is proposed.It consists of one SAW resonator,one series inductor and one parallel inductor.The positions of the transmission zeros and poles are changed through the tuning of the inductor values.In this manner,a desired filter with reconfigurable bandpass-to-bandstop responses and continuously tunable bandwidths is obtained.A bandwidth tunable bandpass-to-bandstop filter and a bandwidth independently tunable dual-band bandpass filter are designed.The measured and simulation results show that the bandwidth adjustment ratios of the bandwidth tunable bandpass-to-bandstop filter are respectively 2.63 and 3.09 in bandpass and bandstop mode.The synchronous and independent tuning of the bandwidth is realized in the bandwidth independently tunable dual-band bandpass filter.The above results prove the feasibility and practicability of the design.