In the paper, a miniaturized wideband rat-race coupler with improved phase performance is designed and analyzed. Flat output ports phase differences are obtained by utilizing a component-loaded T-type transmission line (CLT-TL) with a stub-loaded short-circuited coupled line (SLS-CL). Let the CLT-TL and SLS-CL sections be equivalent to uniform 90° and 270° transmission lines, respectively. Design equations are derived, and an optimization is proceeded to obtain the circuit parameters. For validation, a prototype is designed, fabricated, and measured. Including the feeding lines, the circuit size is 0.31λg × 0.31λg. Under the criterion of return loss (RL) > 10 dB, the measured bandwidths for ports 1 and 3 excitations are both reach 48%. For amplitude imbalance (AP) < 0.5 dB, the overlap relative bandwidth is 46.88%. The measured bandwidths with 2° phase imbalance are 49.58% and 54.01% for ports 1 and 3 excitations, respectively.
2. Chang, W. S., C. H. Liang, and C. Y. Chang, "Slow-wave broadside-coupled microstrip lines and its application to the rat-race coupler," IEEE Microw. Wireless Compon. Lett., Vol. 25, No. 6, 361-363, Jun. 2015.
doi:10.1109/LMWC.2015.2421306
3. Chang, E. S. and C. Y. Chang, "A high slow-wave factor microstrip structure with simple design formulas and its application to microwave circuit design," IEEE Trans. Microw. Theory Techn., Vol. 60, No. 11, 3376-3383, Nov. 2012.
doi:10.1109/TMTT.2012.2216282
4. Wang, C. C., H. C. Chiu, and T. G. Ma, "A slow-wave multilayer synthesized coplanar waveguide and its applications to rat-race coupler and dual-mode filter," IEEE Trans. Microw. Theory Techn., Vol. 59, No. 7, 1719-1729, Jul. 2011.
doi:10.1109/TMTT.2011.2138713
5. Wang, Y. Q., K. X. Ma, N. N. Yan, and L. Y. Li, "A slow-wave rat-race coupler using substrate integrated suspended line technology," IEEE Trans. Compon. Packag. Manuf. Technol., Vol. 7, No. 4, 630-636, Apr. 2017.
doi:10.1109/TCPMT.2017.2661483
6. Tseng, C. H. and H. J. Chen, "Compact rat-race coupler using shunt-stub-based artificial transmission lines," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 11, 734-736, Nov. 2008.
doi:10.1109/LMWC.2008.2005225
7. Tseng, C. H. and C. L. Chang, "A rigorous design methodology for compact planar branch-line and rat-race couplers with asymmetrical T-structures," IEEE Trans. Microw. Theory Techn., Vol. 60, No. 7, 2085-2092, Jul. 2012.
doi:10.1109/TMTT.2012.2195019
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. Microw. Theory Techn., Vol. 52, No. 3, 798-804, Mar. 2004.
doi:10.1109/TMTT.2004.823541
9. Eccleston, K. W. and S. H. M. Ong, "Compact planar microstripline branch-line and rat-race couplers," IEEE Trans. Microw. Theory Techn., Vol. 51, No. 10, 2119-2125, Oct. 2003.
doi:10.1109/TMTT.2003.817442
10. Gu, J. and X. Sun, "Miniaturization and harmonic suppression of branch-line and rat-race hybrid coupler using compensated spiral compact microstrip resonant cell," IEEE MTT-S Int. Microw. Symp. Dig., 1211-1214, 2005.
11. Lee, H. S., K. Choi, and H. Y. Hwang, "A harmonic and size reduced ring hybrid using coupled lines," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 4, 259-261, Apr. 2007.
doi:10.1109/LMWC.2007.892954
12. Ahn, H.-R. and M. M. Tentzeris, "Compact and wideband General Coupled-line Ring Hybrids (GCRHS) for arbitrary circumferences and arbitrary power-division ratios," IEEE Access, Vol. 7, 33414-33423, 2019.
doi:10.1109/ACCESS.2019.2902852
13. Ahn, H.-R. and M. M. Tentzeris, "A novel wideband compact microstrip coupled-line ring hybrid for arbitrarily high power-division ratios," IEEE Trans. Circuits Syst. II, Exp. Briefs, Vol. 64, No. 6, 630-634, Jun. 2017.
doi:10.1109/TCSII.2016.2598227
14. Ahn, H. R. and S. Nam, "Wideband microstrip coupled-line ring hybrids for high power-division ratios," IEEE Trans. Microw. Theory Techn., Vol. 61, No. 5, 1768-1780, May 2013.
doi:10.1109/TMTT.2013.2251654
15. Liang, C. H., W. S. Chang, and C. Y. Chang, "Enhanced coupling structures for tight couplers and wideband filters," IEEE Trans. Microw. Theory Techn., Vol. 59, No. 3, 574-583, Oct. 2011.
doi:10.1109/TMTT.2010.2094202
16. Yeung, L. K. and Y. E. Wang, "A novel 180 hybrid using broadside-coupled asymmetric coplanar striplines," IEEE Trans. Microw. Theory Techn., Vol. 55, No. 12, 2625-2630, Dec. 2007.
doi:10.1109/TMTT.2007.910067
17. Pan, Y. F., S. Y. Zheng, Y. M. Pan, Y. X. Li, and Y. L. Long, "A frequency tunable quadrature coupler with wide tuning range of center frequency and wide operating bandwidth," IEEE Trans. Circuits Syst. II, Exp. Briefs, Vol. 65, No. 7, 864-868, Jul. 2018.
doi:10.1109/TCSII.2017.2738662
18. Zysman, G. I. and A. K. Johnson, "Coupled transmission line networks in an inhomogeneous dielectric medium," ” IEEE Trans. Microw. Theory Techn., Vol. 17, No. 10, 753-759, Oct. 1969.
doi:10.1109/TMTT.1969.1127055
19. Muraguchi, M., T. Yukitake, and Y. Naito, "Optimum design of 3-dB branch-line couplers using microstrip lines," IEEE Trans. Microw. Theory Techn., Vol. 31, No. 8, 674-678, 1983.
doi:10.1109/TMTT.1983.1131568
20. Kennedy, J. and R. Eberhart, "Particle swarm optimization," ICNN95 — International Conference on Neural Networks, 2002.
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