Hilbert‐shaped complementary ring resonator and application to enhanced‐performance low pass filter with high selectivity

In this article, a novel single negative metamaterial (MTM) transmission line (TL) consisting of a Hilbert-shaped complementary ring resonator (H-CRR) on the ground plane is initially presented and studied in depth. Then based on the proposed MTM TL, a novel six-section Hi-Lo microstrip low-pass filter (LPF) with a cut-off frequency 2.5 GHz is developed, fabricated, and measured. Measurement results indicate that: by integrating H-CRR, the selectivity has been significantly improved which is 77.3 dB/GHz due to the single negative permittivity; by etching a crown square on low-impedance section, the bandwidth characterized by 20 dB return loss was obviously enhanced by 26.2% and the maximal sidelobe level of in-band return loss was reduced from 22 to 24.6 dB. What' more, the developed LPF achieved a 36.3% size reduction with respect to its conventional counterpart. The design concept, which was confirmed by the measurement data, is of practical value and can be popularized in other microwave devices where high selectivity is requested. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. © 2011 Wiley Periodicals, Inc.