Reconfigurable And Tunable Microwave Filters

In today's society,wireless communication technology is developing rapidly.At present,5G wireless networks are preparing for operation,and 6G has become a new research focus.At the same time,the previous communication standards are still widely used in some scenarios.The coexistence of multiple communication standards has made spectrum resources more and more precious.In order to improve the utilization of spectrum resources and the capacity of wireless communication systems,spectrum technologies such as frequency hopping,spread spectrum,and multi-frequency are widely used.The key components of these spectrum technologies-reconfigurable filters and multi-frequency filters have become the focus of researchers at home and abroad.At present,researches on reconfigurable filters focus on reconfigurable center frequencies,but research on reconfigurable bandwidths is seriously insufficient.This thesis presents a scheme for reconfigurable bandpass and bandstop filters,which has certain application value.The introduction of this thesis reviews the current development of microwave reconfigurable filter design,and then introduces the basic theory of microwave filter design in Chapter 2.The third chapter of this thesis proposes a combline reconfigurable bandpass filter with binary bandwidth.The ability to reconfigure bandwidth can be introduced by inserting M switchable electrical coupling reducers(SECRs)into each of the internal or external coupling structures of the comb bandpass filter.Each SECR contains a metal strip,one end of which is grounded through a PIN diode switch,which can be switched between open and shorted states.The n SECRs in each coupling structure will provide 2~M circuit states,each state has a different coupling coefficient,thus achieving2~M bandwidths.The thesis designs and processes a second-order bandwidth reconfigurable bandpass filter with four switchable bandwidth states(M=2).The bandwidth is in the range of 35MHz to50MHz and the bandwidth step is 5MHz.The insertion loss of the filter is less than 4 d B.The overall size of the filter is small(38mm*80mm),which is equivalent to the size of a non-reconfigurable microstrip filter.The experimental results agree well with the simulation results.The fourth chapter of this thesis proposes a wideband binary bandwidth reconfigurable parallel stub bandpass filter.By using a parallel short stub combination in place of a single parallel short stub in a traditional structure,the ability to reconfigure bandwidth can be introduced.Each parallel stub combination consists of M switchable short-circuit stubs with different characteristic impedances.Each switchable short-circuit terminal stub consists of a quarter-wavelength stub.One end is connected to the main transmission line through a PIN diode.It can be switched between open and shorted states under the control of external voltage,and the other end is grounded through a DC blocking capacitor.Each parallel stub combination can realize 2~M-1 circuit states under the control of M control voltages.The equivalent characteristic impedance of the parallel stub combination of each state is different,so that 2~M-1 filter bandwidth can be achieved.The fourth chapter of this thesis also proposes a binary bandwidth reconfigurable parallel stub band-stop filter.A parallel open stub combination is used to replace a single parallel open stub in the traditional structure.Each parallel stub combination consists of M switchable parallel open stubs with different characteristic impedances.Each parallel stub combination can achieve 2~M-1 circuit states under the control of M control voltages,the equivalent characteristic impedance of the parallel stub combination of each state is different,so that 2~M-1 filter bandwidths can be realized.The two filters proposed in this chapter have the advantages of more bandwidth states,larger adjustable ranges,and standing waves that do not deteriorate with bandwidth switching.The fifth chapter of the thesis proposes a dual-band band-stop filter(DBBSF)design that combines the traditional quarter-wavelength microstrip band-stop filter structure and the defect ground structure(DGS).The upper quarter-wavelength microstrip resonator introduces a low-frequency stopband,and the open-loop DGS resonator on the ground plane introduces a high-frequency stopband.A reasonable tuning method is used to adjust the center frequency and bandwidth of the two stopbands to meet the design requirements.In this chapter,a third-order dual-band rejection filter is designed and fabricated.The filter has the advantages of compact structure and good frequency selectivity.