A compact microstripbandpass filter using miniaturized hairpin resonators is presented in this letter. Two modified stepped impedance hairpin resonators connected by parallel coupling are designed for the bandpass filter. The proposed miniaturized hairpin resonator is composed of amicrostrip line and rectangular ring structures between parallel high impedance lines. A big capacitance in the hairpin resonator is provided by the gaps ofrectangular ring structures in the parallel high impedance lines. Therefore, the proposed bandpass filter using the hairpin resonators has a low insertion loss, low return loss and compact size. The proposed bandpass filter with acenter frequency of4.96GHz is designed with EM full wave simulator IE3D andverified with experiment.
2. Hsieh, L.-H. and K. Chang, "Compact lowpass filter using stepped impedance hairpin resonator," Electron. Lett., Vol. 37, No. 14, 899-900, 2001.
3. Cho, J. H. and J. C. Lee, "Compact microstrip stepped-impedance hairpin resonator low-pass filter with aperture," Microw. Opt. Technol. Lett., Vol. 46, No. 6, 517-520, 2005.
4. Tu, W.-H. and K. Chang, "Compact microstrip low-pass filter with sharp rejection," IEEE Microw. Wireless Compon. Lett., Vol. 15, No. 6, 404-406, Jun. 2005.
5. Li, L., Z.-F. Li, and J.-F. Mao, "Compact lowpass filters with sharp and expanded stopband using stepped impedance hairpin units," IEEE Microw. Wireless Compon. Lett., Vol. 20, No. 6, 240-242, 2010.
6. Hong, C. J.-S. and M. J. Lancaster, "Couplings of microstrip square open-loop resonators for cross-coupled planar microwave filters," IEEE Trans. Microw. Theory Tech., Vol. 44, 2099, 1996.
7. Pozar, D., "Microwave Engineering," Addison-Wesley, 1993.