Filter synthesis with improved group time delay

Summary form only given. Filters which can give a combination of a sharp cutoff rate outside the passband and a flat response with minimum insertion loss in the passband, having a minimum number of reactive elements are desirable in many applications. In this work new polynomials for filter design are proposed which are obtained as products of lower order Legendre polynomials. Their properties are shown and compared to the traditional filters derived from Butterworth and Chebyshev polynomials. Their frequency response curves give a smoother response in the passband than Chebyshev filters with a remarkable sharper cutoff rate closer to the Chebyshev than the Butterworth ones. Thus, compared with the classical solution of Chebyshev filters, there is less harmonic content in the bandwidth and lower phase distortion, which often is disqualification for video- and data applications. As a result these filters show improved group time delay performance. Tables of element values for low-pass filter prototypes and curves of attenuation versus normalized frequency are given for the design purposes. Designing a microwave band-pass filter shows the extension of the results to other types of filters.