This paper presents a planar filtering magic-T with a simple structure. It consists of four half-wavelength microstrip resonators with one loaded with a shorted microstrip stub at its central location. The resonator loaded with a shorted microstrip stub has the even-symmetry resonant mode. Other three resonators have the odd-symmetry resonant mode. The planar filtering magic-T has four ports, which all adopt a tapped line structure. Its novelty lies in the simple structure. Compared with previous works in the literature, its inter-resonator coupling zones are apart away and have no influence on each other, which means a simple design. Furthermore, a different-properties coupling is not needed, and its filtering response can be easily extended to the high-order case. The operational mechanism and design method are introduced in details. A planar filtering magic-T with center frequency of 920 MHz was designed and fabricated. The measured results show that, at the center frequency, the return losses (S11/S44) is less than 20/12 dB; an isolation degree of 25 dB (S41) can be observed; the insertion loss of the difference port (S21/S31) and sum port (S24/S34) are 4.5/4.7 dB and 4.3/4.6 dB; the phase unbalance is 8˚/7˚(Σ/Δ). Totally, these results can verify the effectiveness of the proposed novel planar fiiltering magic-T.
2. Kim, J. P. and W. S. Park, "Novel configurations of planar multilayer magic-T using microstrip-slotline transitions," IEEE Trans. Microw. Theory Techn., Vol. 50, No. 7, 1683-1688, 2002.
3. He, F. F., K. Wu, W. Hong, H. J. Tang, H. B. Zhu, and J. X. Chen, "A planar magic-T using substrate integrated circuits concept," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 6, 386-388, 2008.
4. Yen, K. U., E. J. Wollack, J. Papapolymerou, and J. Laskar, "A broadband planar magic-T using microstrip-slotline transitions," IEEE Trans. Microw. Theory Techn., Vol. 56, No. 1, 172-177, 2008.
5. Wang, W., T. Shen, T. Huang, and R. Wu, "Miniaturized rat-race coupler with bandpass response and good stopband rejection," 2009 IEEE MTT-S International Microwave Symposium Digest, 709-712, 2009.
6. Chen, C., J. Li, G. Wang, K. Zhou, and R. Chen, "Design of compact filtering 180-degree hybrids with arbitrary power division and filtering response," IEEE Access, Vol. 7, 18521-18530, 2019.
7. Chen, C., T. Huang, C. Chen, W. Liu, T. Shen, and R. Wu, "A compact filtering rat-race coupler using dual-mode stub-loaded resonators," 2012 IEEE MTT-S International Microwave Symposium Digest (MTT), 1-3, 2012.
8. Liu, W., T. Huang, C. Chen, T. Shen, and R. Wu, "Design of a 180-degree hybrid with Chebyshev filtering response using coupled resonators," 2013 IEEE MTT-S International Microwave Symposium Digest (MTT), 1-3, 2013.
9. Lin, T.-W., J.-Y. Wu, and J.-T. Kuo, "Filtering rat-race coupler with transmission zeros using compact miniaturized hairpin resonators," 2015 IEEE International Wireless Symposium (IWS 2015), 1-4, 2015.
10. Lin, C. and J. Kuo, "Compact eighth-order microstrip filtering coupler," 2017 IEEE Asia Pacific Microwave Conference (APMC), 806-808, 2017.
11. Lin, C. and S. Chung, "A compact filtering 180◦ hybrid," IEEE Trans. Microw. Theory Techn., Vol. 59, No. 12, 3030-3036, 2011.
12. Wang, K., X. Y. Zhang, S. Y. Zheng, and Q. Xue, "Compact filtering rat-race hybrid with wide stopband," IEEE Trans. Microw. Theory Techn., Vol. 63, No. 8, 2550-2560, 2015.
13. Matthaei, G. L., L. Young, and E. M. T. Jones, Microstrip Filter, Impedance-matching Networks and Coupling Structures, Artech House, Norwood, MA, 1980.
14. Hong, J. S. and M. J. Lancaster, "Microstrip Filter for RF/Microwave Applications," John Wiley & Sons, 2001.