A novel kind of symmetrical backward-wave coupled-line coupler with arbitrary coupling level is proposed in this paper which is based on resonant-type composite right-/left-handed transmission lines (CRLH TLs). First, an equivalent circuit model and procedure for circuit parameters extraction are presented to reveal the inherent nature of the unit cell of the CRLH coupler. Then a CRLH TL composed of four cascaded unit cells is demonstrated to point out the way to achieve balanced condition. At last, even/odd modes analysis based on full-wave simulation is employed to explain the operating principle of the coupler. Both quasi 0-dB and 3-dB CRLH couplers are demonstrated experimentally. The quasi 0-dB backward coupling is achieved over the range from 1.69 GHz to 2.19 GHz (-3 dB bandwidth in measurement), which represents the fractional bandwidth 25.8%. The maximum coupling coefficient 0.52 dB is obtained at 1.96 GHz, where the directivity and isolation is 20.8 dB and 21.3 dB, respectively. The 3-dB couplers shows an amplitude balance of 2 dB and quadrature phase balance of 90±5 degree over the fractional bandwidth of around 11.4%, from 1.99 to 2.23 GHz.
2. Nguyen, H. V. and C. Caloz, "Simple-design and compact MIM CRLH microstrip 3-dB coupled-line coupler," IEEE MTT-S International Microwave Symposium Digest, 1733-1736, San Francisco, CA, Jun. 2006.
3. Nguyen, H. V. and C. Caloz, "Generalized coupled-mode approach of metamaterial coupled-line couplers: Coupling theory, phenomenological explanation, and experimental demonstration," IEEE Trans. Microw. Theory Tech., Vol. 55, No. 5, 1029-1039, May 2007.
4. Gil, M., J. Bonache, J. Garcia-Garcia, J. Martel, and F. Martin, "Composite right/left-handed metamaterial transmission lines based on complementary split-rings resonators and their applications to very wideband and compact filter design," IEEE Trans. Microw. Theory Tech., Vol. 55, No. 6, 1296-1304, 2007.
5. De la Mata Luque, T. M., N. R. K. Devarapalli, and C. G. Christodoulou, "Investigation of bandwidth enhancement in volumetric left-handed metamaterials using fractals," Progress In Electromagnetics Research, Vol. 131, 185-194, 2012.
6. Chen, J.-X., J. Shi, Z.-H. Bao, and Q. Xue, "Tunable and switchable bandpass filters using slot-line resonators," Progress In Electromagnetics Research, Vol. 111, 25-41, 2011.
7. Segovia-Vargas, D., F. J. Herraiz-Martinez, E. Ugarte-Munoz, L. E. Garcia-Munoz, and V. Gonzalez-Posadas, "Quad-frequency linearly-polarized and dual-frequency circularly-polarized microstrip patch antennas with CRLH loading," Progress In Electromagnetics Research, Vol. 133, 91-115, 2013.
8. Mujumdar, M. D., J. Cheng, and A. Alphones, "Double periodic composite right/left handed transmission line based leaky wave antenna by singular perturbation method," Progress In Electromagnetics Research, Vol. 132, 113-128, 2012.
9. Cao, W.-Q., B. Zhang, A. Liu, T. Yu, D. Guo, and Y. Wei, "Novel phase-shifting characteristic of CRLH Tl and its application in the design of dual-band dual-mode dual-polarization antenna," Progress In Electromagnetics Research, Vol. 131, 375-390, 2012.
10. Shamaileh, K. A. A., A. M. Qaroot, and N. I. Dib, "Non-uniform transmission line transformers and their application in the design of compact multi-band Bagley power dividers with harmonics suppression," Progress In Electromagnetics Research, Vol. 113, 269-284, 2011.
11. Nguyen, H. V. and C. Caloz, "Dual-band CRLH branch-line coupler in MIM technology," Microw. Opt. Techn. Let., Vol. 48, No. 11, 2331-2333, 2006.
12. Gil, M., J. Bonache, J. Selga, J. Garcia-Garcia, and F. Martin, "Broadband resonant-type metamaterial transmission lines," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 2, 97-99, Feb. 2007.
13. Caloz, C. and T. Itoh, Application of the transmission line theory of left-handed (LH) materials to the realization of a microstrip LH line, Antennas and Propagation Society International Symposium, 412-415, Jun. 2002.
14. Falcone, F., T. Lopetegi, J. D. Baena, R. Marques, F. Martin, and M. Sorolla, "Effective negative-epsilon stopband microstrip lines based on complementary split ring resonators," IEEE Microw. Wireless Compon. Lett., Vol. 14, No. 6, 280-282, 2004.
15. Liu, L., C. Caloz, C. C. Chang, and T. Itoh, "Forward coupling phenomena between artificial left-handed transmission lines," J. Appl. Phys., Vol. 92, No. 9, 5560-5565, Aug. 2002.
16. Caloz, C., A. Sanada, L. Liu, and T. Itoh, A broadband left-handed (LH) coupled-line backward coupler with arbitrary coupling level, IEEE MTT-S International Microwave Symposium Digest, 317-320, Philadelphia, PA, Jun. 2003.
17. Jarauta, E., et al., Metamaterial microstrip backward couplers for fully planar fabrication techniques, Proc. Joint 29th Int. Conf. Infrar. Millim. Waves 12th Int. Conf. Terahertz Electron., 185-186, Sep. 27-Oct. 1, 2004.
18. Bonache, J., M. Gil, I. Gil, J. Garcia-Garcia, and F. Martin, "On the electrical characteristics of complementary metamaterial resonators," IEEE Microw. Wireless Compon. Lett., Vol. 16, No. 10, 543-545, 2006.
19. Gil, M., J. Bonache, I. Gil, J. Garcia-Garcia, and F. Martin, "On the transmission properties of left-handed microstrip lines implemented by complementary split rings resonators," International Journal of Numerical Modelling: Electronic Networks, Devices and Fields, Vol. 19, No. 2, 87-103, 2006.
20. Gil, I., J. Bonache, M. Gil, J. Garcia-Garcia, and F. Martin, "Left-handed and right-handed transmission properties of microstrip lines loaded with complementary split rings resonators," Microw. Opt. Techn. Let., Vol. 48, No. 12, 2508-2511, 2006.
21. Lin, X., P. Su, Y. Fan, and Z. B. Zhu, "Improved CRLH-TL with arbitrary characteristic impedance and its application in hybrid ring design," Progress In Electromagnetics Research, Vol. 124, 249-263, 2012.
22. Mongia, R., I. J. Bahl, P. Bhartia, and S. J. Hong, RF and Microwave Coupled-line Circuits, Artech House, Norwood, MA, 1999.
23. Caloz, C. and T. Itoh, "Novel microwave devices and structures based on the transmission line approach of meta-materials," IEEE MTT-S International Microwave Symposium Digest, 195-198, Philadelphia, PA, Jun. 2003.