Distributed Cross-Coupled Non-Reciprocal Bandpass Filters for Mobile Communications

In this paper, we demonstrate for the first time a 4th order non-reciprocal filter with sharp cut-off using a cross-coupled distributed network. The non-reciprocity is brought about by the time modulation of space separated resonators using sinusoids having progressive phase shifts. The sharp cutoff is brought about by inserting transmission zeroes at finite frequencies using cross-coupled network. The circuit is designed using parallel coupled microstrip technology and the simulated results show enhanced results in terms of insertion loss, return loss, isolation, and sharp cutoff suited for mobile communications. More than 15 dB isolation has been achieved without compromising the insertion and the return loss throughout the passband.