Digital-Filter-Based Flat-Group-Delay RF Analog Circuits: Application to Dolph-Chebyshev Windows

The direct synthesis of a family of digital-filter-based RF analog circuits with transmission zeros (TZs) and constant-group-delay behavior is reported. The adopted RF circuit consists of a transversal filtering network composed of transmission-line segments that are connected through a multi-way power divider and combiner at its input and output terminals, respectively. The synthesis procedure starts by obtaining the coefficients of a finite-impulse-response (FIR) digital filter of interest and finalizes with the determination of the electrical parameters of the RF circuit. In particular, designs corresponding to Dolph-Chebyshev windows are addressed in this brief. For experimental-demonstration purposes, two 5-GHz proof-of-concept microstrip prototypes of a symmetrical-quasi-reflectionless bandpass filter (BPF) with Dolph-Chebyshev-type response and the in-series cascade connection of two replicas of it are designed, manufactured, and tested.