Common-Mode Suppression in Microstrip Differential Lines by Means of Complementary Split Ring Resonators: Theory and Applications

• Published in: IEEE transactions on microwave theory and techniques Vol. 60; no. 10; pp. 3023 - 3034
• Main Authors: Naqui, J., Fernandez-Prieto, A., Duran-Sindreu, M., Mesa, F., Martel, J., Medina, F., Martin, F.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.10.2012; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Balancing; Bandwidth; Circuit properties; Circuits; Complementary split-ring resonator (CSRR); Couplings; differential transmission lines; Dispersion; Dispersions; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Equivalent circuits; Exact sciences and technology; Frequency filters; Ground plane; Integrated circuit modeling; Materials; metamaterial-inspired lines; Microstrip; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Microwaves; Oscillators, resonators, synthetizers; Rejection; Resonant frequency; Resonators; split-ring resonator (SRR); Strategy; Ground plane; Complementary split-ring resonator (CSRR); Dispersion relation; differential transmission lines; Microstrip line; Common mode rejection rate; split-ring resonator (SRR); Mode filter; Engraving; Transmission line; metamaterial-inspired lines; Wide band; Ring resonator; Band pass filter; Printed circuit; Metamaterial
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2012.2209675

This paper is focused on the application of complementary split-ring resonators (CSRRs) to the suppression of the common (even) mode in microstrip differential transmission lines. By periodically and symmetrically etching CSRRs in the ground plane of microstrip differential lines, the common mode can be efficiently suppressed over a wide band whereas the differential signals are not affected. Throughout the paper, we present and discuss the principle for the selective common-mode suppression, the circuit model of the structure (including the models under even- and odd-mode excitation), the strategies for bandwidth enhancement of the rejected common mode, and a methodology for common-mode filter design. On the basis of the dispersion relation for the common mode, it is shown that the maximum achievable rejection bandwidth can be estimated. Finally, theory is validated by designing and measuring a differential line and a balanced bandpass filter with common-mode suppression, where double-slit CSRRs (DS-CSRRs) are used in order to enhance the common-mode rejection bandwidth. Due to the presence of DS-CSRRs, the balanced filter exhibits more than 40 dB of common-mode rejection within a 34% bandwidth around the filter pass band.