Linear Time-Invariant Behavioral Digital Models of Frequency-Periodic RF/Microwave Filters

Analog RF/microwave passive filters are traditionally realized by means of electromagnetically-coupled-resonator circuit networks. Nevertheless, alternative design techniques can be exploited to synthesize advanced filtering transfer functions, such as those based on signal-interference principles and generalized stub-loaded-circuit approaches. Contrary to the filtering responses that are synthesized through conventional coupling-matrix-based procedures, the theoretical power transmission parameters of these filtering circuits are usually frequency periodic. Hence, they can be directly matched with the frequency response of an associated digital model. In this paper, this behavioral methodology is applied to the design of novel linear time-invariant digital systems with transfer functions that are inspired by frequency-periodic analog RF/microwave passive filters. Specifically, the coefficients corresponding to the two following synthesis examples are extracted and presented: i) signal-interference quasi-elliptic-type bandpass filter with in-band linear-phase profile and ii) stub-loaded-based dual-passband filter with multiple transmission zeros (TZs). Furthermore, the properties of their associated analog-inspired linear time-invariant digital systems are discussed.