A new method to design a miniaturized ring coupler consisting of multiple open stubs on the inside of the ring is proposed. It is shown that this coupler topology may be seen as fully-distributed composite right/left handed (CRLH) small-size phase shifters, cascaded in a ring configuration. The CRLH phase shifter is analyzed in detail and a design method is proposed, pointing out the condition to obtain a reduction of its length. Using the fully-distributed CRLH based phase shifter, a ring coupler is configured and analyzed in comparison with the traditional ring coupler, showing that both couplers have similar characteristics. To validate the proposed design method, a 3-dB CRLH based ring coupler is designed and fabricated. The experimental results show a very good agreement with the predicted results obtained by electromagnetic simulation. The printed area of the fabricated coupler is 49% smaller compared to the traditional ring coupler.
2. Kim, , D. I. and G. S. Yang, "Design of new hybrid-ring directional coupler using /8 or /6 sections," IEEE Trans. on Microwave Theory and Techniques, Vol. 39, 1179-1784, 1991.
3. Coupez, , J. P., A. Peden, and C. Person, "Analysis and design of ultra miniature hybrid ring directional coupler," Proc. 22nd European Microwave Conf., Vol. 1, 443-447, 1992.
4. Murgulescu, , M. H., , M. Moisan, P. Legaud, E. Penard, and I. Zaquine, "New wideband, 0.67g circumference 180 hybrid ring coupler," Electronics Letters, Vol. 30, No. 4, 299-300, 1994.
5. Murgulescu, , M. H., E. Penard, and I. Zaquine, "Design formulas for generalized 180 hybrid ring couplers," Electronics Letters, Vol. 30, No. 7, 573-574, 1994.
6. Wang, T. and K.Wu, "Size-reduction and band-broadening design technique of uniplanar hybrid ring coupler using phase inverter for M(H)MIC's," IEEE Trans. on Microwave Theory and Techniques, Vol. 47, 198-206, 1999.
7. Chi, , P. L., "Miniaturized ring coupler with arbitrary power divisions based on the composite right/left-handed transmission lines," IEEE Microwave and Wireless Components Letters, Vol. 22, 170-172, 2012.
8. Okabe, , H., C. Caloz, and T. Itoh, "A compact enhanced-bandwidth hybrid ring using an artificial lumped-element left-handed transmission-line section," IEEE Trans. on Microwave Theory and Techniques, Vol. 52, 798-804, 2004.
9. Fouda, , A. E., A. M. E. Safwat, and H. El-Hennawy, "On the applications of the coupled-line composite right/left-handed unit cell," IEEE Trans. on Microwave Theory and Techniques,, Vol. 58, 1584-1591, 2010.
10. Chuang, M. L., "Miniaturized ring coupler of arbitrary reduced size," IEEE Microwave and Wireless Components Letters, Vol. 15, 16-18, 2005.
11. Simion, , S., "Small-size ring coupler design method based on fully distributed composite right/left handed approach ," Electronics Letters,, Vol. 48, No. 23, 1481-1483, 2012.
12. Kim, , D. I. and Y. Naito, "Broad-band design of improved hybrid-ring 3-dB directional couplers," IEEE Trans. on Microwave Theory and Techniques, Vol. 30, No. 11, 2040-2046, 1982.
13. Ho, , C. H., , L. Fan, and K. Chang, "Broadband uniplanar hybrid ring coupler," Electronics Letters , Vol. 29, No. 1, 44-45, 1993.
14. Chi, P. L. and T. Itoh, "Miniaturized dual-band directional couplers using composite right/left-handed transmission structures and their applications in beam pattern diversity systems," IEEE Trans. on Microwave Theory and Techniques, Vol. 57, 1207-1215, 2009.
15. Pozar, , M. D., Microwave Engineering, 3rd Ed., Wiley, New York, 2005.