Multiband Filter Design from Bandpass Prototype Filter with using Frequency Transformation via SRFT

Abstract

Multiband filter design problem includes both analytical and implementation aspects. The main interest is defining a Transducer Power Gain (TPG) function characteristic over frequency bands. It is demanded to suppress or amplify the TPG at certain frequencies. In this study a new method is presented for creating the multiband response with using well defined analytical approach. A transformer-less bandpass filter prototype is synthesized with using well known Simplified Real Frequency Technique (SRFT) and multiband characteristic is derived with applying a basic frequency transformation on the bandpass prototype filter. A double band filter design example is prensented. Descriptive functions of each sections are given in scattering polynomail form. Certain advantages are provided with using this method besides the sequential application of basic low pass to band pass transfromation on a low pass transfer function such as low counts of elements, controlling the filter roll off, easy conversion to distributed domain without probable parasitic couplings.