Design And Research Of CPW Microwave Wide Stopband Filter

With the stimulating demand for wireless communication equipment,more and more wireless devices are flooding all aspects of life.As a result,the electromagnetic spectrum has become increasingly crowded,and the interference between wireless communication devices has become a problem for electromagnetic engineers and scholars.As an important component of the communication system,microwave filter plays an important role in the frequency selection and suppression of other frequency band signals in communication equipment.Therefore,in today's increasingly complex electromagnetic environment,microwave filters with wide stopband suppression have become a popular research direction.Moreover,with the trend of high integration and miniaturization of microwave circuits,coplanar waveguide is more and more used in microwave integrated circuits because it is easy to connect with other components,and has the advantages of simple structure,flexible design and low cost.Firstly,based on the synthesis theory of generalized Chebyshev N+2 coupling matrix,the synthesis process of coupling matrix is programmed by using MATLAB,and the correctness of the program is verified by an example.Secondly,based on the analysis of the resonant characteristics of a Conductor-backed coplanar waveguide?CPW?cavity,the second harmonic is shifted to the high frequency near the third harmonic by adding a grounded through-hole,and then a slot-coupled feed structure is used to generate a transmission zero at the high frequency to suppress the second and third harmonics simultaneously.Finally,by increasing the surface current path of the filter and moving the passband to a lower frequency,a single-cavity CPW broadband filter with stopband rejection less than-17 dB and stopband width of 6.541)₀?1?₀ is the center frequency of the filter)is obtained.In addition,a wide stopband CPW filter with stopband rejection less than-20 dB and stopband width of 7.291)₀ is obtained by making the input port orthogonal to output port.Both filters are processed.Finally,on the basis of single-cavity wide-stopband CPW filter,a dual-cavity CPW filter with wide stopband characteristics is proposed by using NRN?Non-Resonating-Node?cascade method,and its input and output ports are also orthogonal.Two dual-cavity wide-stopband CPW filters are obtained.The stopband rejection of“Direct”and“Orthogonal”CPW filters are-28 dB and-38 dB,respectively.Besides,their width of bandstop are 5.311)₀ and 5.231)₀,respectively.Their coupling topologies are proposed,and the relationship between the structural parameters of the cascaded NRN and the coupling strength of the modes in the two cavities is analyzed.The two dual-cavity CPW filters are fabricated and measured,and the measured results are in good agreement with the simulated results.In addition to the mentioned above,the CPW filter with dual-band characteristic is simulated and analyzed on the basis of single-cavity CPW resonators,and the coupling matrices of two passbands are extracted.