This paper introduces an optimal design method of constant-delay filter. Our aim is to design a filter having high selectivity and constant group-delay within the pass-band and according with the demand of equal pass-band attenuation ripple

to meet the requirements of distortionless transmission of television

facsimile and data signals. Starting directly with the group delay

we use electronic computer with high speed and improved damping least square method to carry out optimal approximation. A desired filter is then designed through several times of iteration. This method has been proved to be very efficient by the fabrication and testing of actual design examples.