Implementation of harmonics-free narrow-band microstrip bandpass filter using complementary split ring resonator

Abstract

This article discusses harmonics-rejected microstrip narrow-band bandpass filter (NBBPF) using complementary split ring resonator (CSRR) structure. The proposed harmonics-rejected NBBPF is first derived from the established lumped element LC bandpass filter (BPF) and then converted into a distributed microstrip BPF by using series and open transmission line stubs. This microstrip BPF resonates with centre frequency fo and its 2nd- and 3rd-order harmonics (2fo and 3fo) because of their inherent nature. These unwanted 2nd- and 3rd-order harmonics will degrade the overall performance of wireless systems. Therefore harmonics rejection is the best solution to boost the behaviour of wireless systems. The harmonics-rejection behaviour of this microstrip BPF is improved by embedding CSRR in its ground plane. In order to verify the superior performance of the desired design, distributed BPF is designed, simulated, realised and tested. To authenticate the harmonics-rejection ability of the proposed BPF, BPFs with and without CSRRs are fabricated and the experimental results are compared. This comparison shows that the projected design has acceptable bandpass frequency responses to the fo and wide stop-band performance in 2fo and 3fo because 2nd- and 3rd-order harmonics are suppressed by the CSRRs. The measured results are in line with the simulated results. The performance valuation plainly indicates that the proposed design both has superior harmonics-rejection ability and is also very easy to manufacture. Hence, the planned NBBPFs have the potential to be an ultimate device in future harmonics-free narrow-band communication system with minimum design complexity.