Novel compact dual-band branch-line couplers are presented. By using ahalf elliptical-ring impedance stub as a basic unit, dual-band branch-line couplers are obtained. Sincea couple of half elliptical-ring impedance stubs can be folded inward to its enclosed areawithout overlap, the branch-line couplercan be miniaturized. In order to verify the effectiveness of the half elliptical-ring impedance stub, two different branch-line couplers operating at 2.4/5.8 GHz are designed, fabricated and tested. Measured results agree well with simulated ones. Compared with the stepped-impedance-stub branch-line couplers, sizes of the proposed couplers are reduced by 43% and 30%, respectively.
2. Park, M.-J. and B. Lee, "Dual-band, cross coupled branch line coupler," IEEE Microwave Wireless Components Letters, Vol. 15, No. 10, 655-657, Oct. 2005.
3. Collado, C., A. Grau, and F. De Flaviis, "Dual-band planar quadrature hybrid with enhanced bandwidth response," IEEE Transactions on Microwave Theory and Techniques, Vol. 54, No. 1, 180-188, Jan. 2006.
4. Zhang, H. L. and H. L., "A stub tapped branch-line coupler for dual-band operations," IEEE Microwave Wireless Components Letters, Vol. 17, No. 2, 106-108, Feb. 2007.
5. Tanaka, H., Y. Sasaki, T. Hashimoto, Y. Yagi, and Y. Ishikawa, "Miniaturized 90 degree hybrid coupler using high dielectric substrate for QPSK modulator," IEEE MTT-S International Microwave Symposium Digest, Vol. 2, 793-796, Jun. 1996.
6. Toyoda, I., T. Hirota, T. Hiraoka, and T. Tokumitsu, "Multilayer MMIC branch-line coupler and broad-side coupler," IEEE Microwave and Millimeter-Wave Monolithic Circuits Symposium Digest, 79-82, Jun. 1992.
7. Eccleston, K. W. and S. H. M. Ong, "Compact planar microstripline branch-line and rat-race couplers," IEEE Transactions on Microwave Theory and Techniques, Vol. 51, No. 10, 2119-2115, Oct. 2003.
8. Sheta, A. F., A. S. Mohra, and S. F. Mahmoud, "A new class of miniature quadrature couplers for MIC and MMIC applications," Microwave and Optical Technology Letters, Vol. 34, No. 3, 215-219, Aug. 2002.
9. 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 Transactions on Microwave Theory and Techniques, Vol. 60, No. 7, 2085-2092, Jul. 2012.
10. Ahn, H. R. and S. Nam, "Compact microstrip 3-dB coupled-line ring and branch-line hybrids with new symmetric equivalent circuits," IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 3, 1067-1078, Feb. 2013.
11. Chin, K. S., K. M. Lin, Y. H, and Wei, "Compact dual-band branch-line and rat-race couplers with stepped-impedance-stub lines," IEEE Transactions on Microwave Theory and Techniques, Vol. 58, No. 5, 1213-1221, May 2010.