Optimization Design of Amplitude-Frequency Arithmetic Symmetry Linear Phase Filter

This paper proposes a direct coupling filter optimal design method in order to solve contradiction between the filter´s amplitude-frequency characteristic arithmetic symmetry and the phase-frequency straightness. Based on the circuit designed by network synthesis method, this paper applies pole placement and circuit optimization techniques to obtain arithmetic symmetrical amplitude-frequency characteristic. Then group delay equalizer is coupled to the circuit, the phase-frequency characteristic using least square method is approached to a straight line, and the coupled circuit is optimized by unconstrained optimization method. The simulation results indicate that the proposed method can get arithmetic symmetrical amplitude-frequency and preferable group delay characteristics in passband. The designed circuit has merits of simple structure, less order, and lower insertion loss.