A straight split dual-mode microstrip resonator is proposed. The frequencies of the two first oscillation modes in the resonator may be brought closer together by adjusting a split parameter whereas the frequency of the third mode remains approximately equal to the doubled average frequency of the first and the second modes. It is shown that formulas derived within 1D model give qualitatively true relations between the resonant frequencies and the structure parameters of the resonator. Examples of narrowband bandpass filters of the fourth and the sixth order are described. Transmission zeros below and above the passband substantially improve the filter's performance. The simulated frequency response of the three-resonator dual-mode filter is compared with the measured response of the fabricated filter.
2. Chen, H.-J., T.-H. Huang, L.-S. Chen, J.-H. Horng, and M.-P. Houng, "New design concept of dual-mode bandpass filter by using nonorthogonal input and output ports for wireless application," Microwave and Optical Technology Letters, Vol. 48, 639-641, Apr. 2006.
3. Wang, H. and L. Zhu, "Microstrip dual-mode filters with miniaturized size and broadened stopband using meander-shaped stepped-impedance ring resonator," IEICE Electronics Express, Vol. 2, 159-164, Mar. 2005.
4. Helvaci, A. K., C. Karpuz, and A. Görür, "Compact dual-mode microstrip resonator for 900MHz bandpass filter applications," Microwave and Optical Technology Letters, Vol. 45, 376-377, Jun. 2005.
5. Makimoto, M. and S. Yamashita, "Bandpass filters using parallel coupled stripline stepped impedance resonators," IEEE Trans. Microw. Theory Tech., Vol. 28, 1413-1417, Dec. 1980.
6. Zhu, L., S. Sun, and W. Menzel, "Ultra-wideband (UWB) bandpass filters using multiple-mode resonator," IEEE Microwave and Wireless Components Letters, Vol. 15, 796-798, Nov. 2005.
7. Hua, C., C. Miao, B. Li, H. Wang, and W. Wu, "Dual-mode bandpass filter using internally coupled stub-loaded resonators," Microwave and Optical Technology Letters, Vol. 53, 643-646, March 2011.
8. Hua, C., C. Miao, B. Li, H. Wang, and W. Wu, "Microstrip bandpass filters using dual-mode resonators with internal coupled lines," Progress In Electromagnetics Research C, Vol. 21, 99-111, 2011.
9. Belyaev, B. A., Yu. G. Shikhov, and P. N. Sergienko, "Spektr of own oscillations of an irregular microstrip resonator," Proc. 1998 4th International Conference on Actual Problems of Electronic Instrument Engineering, APEIE-98, Vol. 2, 105-106, Novosibirsk, Sep. 1998.
10. Tyurnev, V. V., "Coupling coe±cients of resonators in microwave filter theory," Progress In Electromagnetics Research B, Vol. 21, 47-67, 2010.
11. Dovbysh, I. A. and V. V. Tyurnev, "Synthesis and investigation of three-section microstrip filter on folded dual-mode stepped-impedance resonators," Progress In Electromagnetics Research M, Vol. 12, 17-28, 2010.