Design of Trapezoidal-DMS Structured Filters by Direct Bandpass Synthesis Methods

This paper describes a method of direct bandpass synthesis of ladder-DMS hybrid structure filter based on Chebyshev filter function. This method overcomes the complexity and structural limitation of traditional design methods and combines the advantages of the two structures. According to the design requirements of the filter, the direct bandpass synthesis method takes the transmission zero and return loss as initial conditions, and first calculates the characteristic polynomial of the filter function. Then, according to the circuit relationship such as Kirchhoff's law, the impedance and admittance of the circuit are expressed by characteristic polynomials, and the parameters of each element of the resonator are extracted by impedance or admittance and converted into BVD parameters. In order to prove the effectiveness of the method, a BAND25 RX ladder-DMS filter is designed, and the advantages of the bandpass synthesis method compared with the traditional design method are analyzed.