A compact Pi-structure transformer operating arbitrary dual band is proposed in this paper. To achieve the ideal impedance matching, the exact design formulas with no restrictions are obtained. In addition, it is found that there are infinite solutions for this novel transformer considering the fact that three independent variables exist in two equations. And to verify the design formulas, the reflection characteristics in different cases are shown by numerical simulations. The horizontal length of this transformer is half of the Monzon's dual band transformer. The proposed dual band transformer can be used in many compact dual band components design such as antennas, coupler and power dividers.
2. Mitilineos, S. A., S. C. Thomopoulos, and C. Capsalis, "Genetic design of dual-band, switched-beam dipole arrays, with elements failure correction, retaining constant excitation coefficients," Journal of Electromagnetic Waves and Applications, Vol. 20, 1925-1942, 2006.
3. He, Z., X.-L. Wang, S. Han, T. Lin, and Z. Liu, "The synthesis and design for new classic dual-band waveguide band-stop filters," Journal of Electromagnetic Waves and Applications, Vol. 22, 119-130, 2008.
4. Guo, C., H.-J. Sun, and X. Lu, "A novel dualband frequency selective surface with periodic cell perturbation," Progress In Electromagnetics Research B, Vol. 9, 137-149, 2008.
5. Zainud-Deen, S. H., S. M. Gaber, and S. M. M. Ibrahem, "Built-in dual frequency antenna with an embedded camera and a vertical ground plane," Progress In Electromagnetics Research Letters, Vol. 3, 51-60, 2008.
6. Chow, Y. L. and K. L. Wan, "A transformer of one-third wavelength in two sections-for a frequency and its first harmonic," IEEE Microw. Wireless Compon. Lett., Vol. 12, No. 1, 22-23, 2002.
7. Monzon, C., "Analytical derivation of a two-section impedance transformer for a frequency and it first harmonic," IEEE Microw. Wireless Compon. Lett., Vol. 12, No. 10, 381-382, 2002.
8. Monzon, C., "A small dual-frequency transformer in two sections," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 4, 1157-1161, 2003.
9. Wu, L., Z. Sun, H. Yilmaz, and M. Berroth, "A dual-frequency wilkinson power divider," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 1, 278-284, 2006.
10. Wu, L., H. Yilmaz, T. Bitzer, A. Pascht, and M. Berroth, "A dual-frequency Wilkinson power divider: For a frequency and its first harmonic," IEEE Microw. Wireless Compon. Lett., Vol. 15, No. 2, 107-109, 2005.
11. Kawai, T., Y. Jun, Y. Kokubo, and I. Ohta, "A design method of dual-frequency wilkinson power divider," Asia-Pacific Microwave Conference (APMC), 913-916, 2006.
12. Wu, Y. L., H. Zhou, Y.-X. Zhang, and Y.-A. Liu, "An unequal wilkinson power divider for a frequency and its first harmonic," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 11, 737-739, 2008.
13. Wu, Y., Y. Liu, Y. Zhang, J. Gao, and H. Zhou, "A dual band unequal wilkinson power divider without reactive components," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 1, 216-222, 2009.
14. Cheng, K. K. M. and F. L. Wong, "A novel approach to the design and implementation of dual-band compact planar 900 branch-line coupler," IEEE Trans. Microw. Theory Tech., Vol. 52, No. 11, 2458-2463, 2004.
15. Mohra, A. S. S., "Compact dual band Wilkinson power divider," Microwave and Optical Technology Letters, Vol. 50, No. 6, 1678-1682, 2008.
16. Pozar, D. M., Microwave Engineering, 3rd Ed., Wiley, New York, 2005.
17. Milligan, T. A., "Transmission-line transformation between arbitrary impedances," IEEE Trans. Microw. Theory Tech. (Letters), Vol. 24, 159, 1976.
18. Potok, M. H. N., "Comments on `transmission-line transformation between arbitrary impedances'," IEEE Trans. Microw. Theory Tech. (Letters), Vol. 25, No. 77, 1977.