A novel rat-race coupler with wide adjustable range of power-dividing ratio and uncrossed input/output ports is presented by using coupling adjustable trans-directional (TRD) coupled lines, parallel coupled lines and a 180° phase shifting line. Wide adjustable range of power-dividing ratios is accomplished by varying the coupling of the TRD coupled lines. Moreover, with the combination of the TRD coupled lines and parallel coupled lines, the input and output ports of the rat-race coupler are uncrossed. The structure of the proposed rat-race coupler is analyzed, and the design equations are derived. As an example to validate the feature of the proposed rat-race coupler, a prototype operating at 1.6 GHz is devised, fabricated and measured. The measured results show that the designed coupler has a wide adjustable range (-7 ~ 15 dB) of power dividing ratio with a controlled voltage range of 3.5 to 13.5 V.
2. Alimenti, F., P. Mezzanotte, S. Giacomucci, M. Dionigi, C. Mariotti, M. Virili, and L. Roselli, "24 GHz single-balanced diode mixer exploiting cellulose-based materials," IEEE Microw. Wireless Compon. Lett., Vol. 23, No. 11, 596-598, 2013.
3. Gandini, E., M. Ettorre, R. Sauleau, and A. Grbic, "A lumped-element unit cell for beam-forming networks and its application to a miniaturized butler matrix," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 4, 1477-1487, 2013.
4. Fardin, E. A., A. S. Holland, and K. Ghorbani, "Electronically tunable lumped element 90◦ hybrid coupler," Electronics Letters, Vol. 42, No. 6, 2006.
5. Djoumessi, E. E., E. Marsan, C. Caloz, M. Chaker, and K. Wu, "Varactor tuned dual band quadrature hybrid coupler," IEEE Microwave Compon. Lett., Vol. 16, No. 11, 603-605, Nov. 2006.
6. Ferrero, F. and G. Jacquemod, "A tunable quasi-lumped microstrip coupler and RF applications," IEEE/MTT-S International Microwave Symposium, 2007.
7. Hsieh, H. H., Y. T. Liao, and L. H. Lu, "A compact quadrature hybrid MMIC using CMOS active inductors," IEEE Trans. Microwave Theory Tech., Vol. 55, No. 6, 1098-1104, Jun. 2007.
8. Lehmann, T., H. Mextorf, and R. Knoechel, "Design of quadrature directional couplers with continuously variable coupling ratios," Proc. Eur. Microw. Conf., 199-202, 2008.
9. Yeung, L. K., "A compact directional coupler with tunable coupling ratio using coupled-line sections," Proc. Asia-Pacific Microw. Conf., 1730-1733, 2011.
10. Abdalla, M. A. Y., K. Phang, and G. V. Eleftheriades, "A compact highly reconfigurable CMOSMMIC directional coupler," IEEE Trans. Microw. Theory Tech., Vol. 56, No. 2, 305-319, Feb. 2008.
11. Hur, B. and W. R. Eisenstadt, "Tunable broadband MMIC active directional coupler," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 1, 168-176, Jan. 2013.
12. Zhou, M., B. Arigong, H. Ren, R. G. Zhou, and H. L. Zhang, "A varactor based 90 directional coupler with tunable coupling ratios and reconfigurable responses," IEEE Trans. Microw. Theory Tech., Vol. 62, No. 3, 416-421, Mar. 2014.
13. Cheng, K. K. M. and S. Yeung, "A novel rat-race coupler with tunable power dividing ratio, ideal port isolation, and return loss performance," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 1, 55-60, 2013.
14. Cheng, K. K. M. and M. C. J. Chik, "A frequency-compensated rat-race coupler with wide bandwidth and tunable power dividing ratio," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 8, 2841-2847, 2013.
15. Wang, Z. B., Y. Cao, S. J. Fang, and Y. A. Liu, "Miniaturized rat-race coupler with tunable power dividing ratio based on open-and short-circuited transdirectional coupled lines," Microwave Opt. Technol. Lett., Vol. 58, No. 11, 2683-2689, 2016.
16. Napijalo, V. and B. Kearns, "Multilayer 180 hybrid coupler," IEEE Trans. Microw. Theory Tech., Vol. 56, No. 11, 2525-2535, Nov. 2008.
17. Napijalo, V., "Coupled line 180 hybrids with lange couplers," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 12, 3674-3682, Dec. 2012.
18. Liu, H. M., S. J. Fang, and Z. B. Wang, "Novel coupled line 180 hybrid with non-interspersed input and output ports," IEEE Trans. Microw. Theory Tech., Vol. 62, No. 11, 2641-2649, Nov. 2014.
19. Collin, R. E., Foundations for Microwave Engineering, 2nd Ed., McGraw-Hill, New York, NY, USA, 1992.