Research Of Microstrip Resonator And The Design Of Compact Microwave Filter

Modern microwave filters are widely used in daily life(such as the relay communication systems,mobile radio communication systems,etc.)and military defense(such as satellite communication systems,electronic warfare systems and radar communication systems,etc.).Thus,it is significant to design low cost,compact,high perform filters to meet the need in rapid development communications systems in recent years.Because of the compact structure,high integration density,low cost and easy processing,the microstrip filter has been attracted much attention among kinds of filters.Firstly,this paper introduced the background and design theories of the filter.Then,according to the actual application of the microwave filter,the significance of designing a high performance filter is explained;the function polynomials and characteristic polynomials of the classical filter prototypes are introduced,and the theory of transmission lines and coupling matrix theory of generalized Chebyshev filter are summarized.Then,in this paper,a lowpass filter(LPF)is proposed based on a new type broad band stop resonator and a complementary split-ring resonator(CSRR)attached with two C-shaped defect ground structures(DGS).The LPF was designed using the first two resonant points produced by the composite resonator,and operating mechanisms are investigated based on its equivalent models.The LPF is fabricated and measured,the measured results are in good agreement with the full-wave simulated results,showing the merits of compact size and sharp roll-off.Furthermore,in this paper,the equivalent circuit applied lumped elements was proposed to characterize the transmission characteristics of the spiral-shaped DGS.Parameters of the equivalent circuit were extracted based on three characteristic frequencies.To verify the feasibility of the equivalent circuit,a third order BPF were designed with two spiral-shaped defected ground structures and a microstrip resonator.Then,the proposed equivalent circuit was used to demonstrate the filter responses.The simulation results of the two filters showed good consistency with the analysis results.Finally,the third order BPF was fabricated and measured,the measured results agree well with the simulations.Finally,a novel spiral DGS resonator with two spiral stubs and a center stub was presented in this paper.Full-wave simulation was used to investigate the working principle of the resonator.The results show that the spiral resonator has two operating modes,so that it can produce two resonant frequencies.It is also found that it is convenient to control the two resonant frequencies by adjusting the dimensions of the two spiral stubs and the center stub.A dual-band bandpass filter(BPF)was designed using two resonators of this type and a T-shaped coupling node,having a bandwidth of 4.5% at 1.87 GHz and a bandwidth of 3.3% at 2.43 GHz.The measured results of the designed dual-band BPF agree well with the simulated responses.