This paper presents a novel quasi-elliptic function lowpass filter (LPF) by using quasi-lumped elements. The proposed LPF is firstly based on a seven-order Chebyshev response lowpass prototype. Then, a series branches of shunt resonant LC circuit is introduced in the filter design to provide a transmission zero close to the transition band, which can improve the roll-off rate of proposed LPF significantly. To implement the lumped elements of lowpass prototype, the high-impedance meander lines are employed to realized the inductors while inter-digital microstrip lines and the microstrip parallel-plate structures are used to realize the capacitors. To validate the proposed method, a LPF with 3 dB cutoff frequency fc at 1.9 GHz is designed and fabricated. The measured results show that the fabricated LPF has a sharp roll-off rate up to -142 dB/octave and -15 dB harmonic suppression from 1.1fc to 9.7fc. Moreover, the fabricated LPF also has a compact size of 0.1λgc × 0.11λgc. Good agreement can observed between the simulation and measurement.
2. Li, L., Z.-F. Li, and Q.-F. Wei, "Compact and selective lowpass filter with very wide stopband using tapered compact microstrip resonant cells," Elecron. Lett., Vol. 45, No. 5, 267-268, 2009.
3. Li, J.-L., S.-W. Qu, and Q. Xue, "Compact microstrip lowpass filter with sharp roll-off and wide stop-band," Elecron. Lett., Vol. 45, No. 2, 110-111, 2009.
4. Li, K., M. Zhao, Y. Fan, Z. Zhu, and W. Cui, "Compact lowpass filter with wide stopband using novel double-folded SCMRC structure with parallel open-ended stub," Progress In Electromagnetics Research Letters, Vol. 36, 77-86, 2013.
5. Ka, K. and K. S. Yeo, "New ultra-wide stopband low-pass filter using transformed radial stubs," IEEE Trans. Microw. Theory Tech., Vol. 59, No. 3, 604-611, 2011.
6. Cao, H., W. Guan, S. He, and L. Yang, "Compact lowpass filter with high selectivity using G-shaped defected microstrip structure ," Progress In Electromagnetics Research Letters, Vol. 33, 55-62, 2012.
7. Chen, Q. and J. Xu, "DGS resonator with two transmission zeros and its application to lowpass filter design," Elecron. Lett., Vol. 46, No. 21, 1447-1449, 2010.
8. Al Sharkawy, M. H., D. Abd El-Aziz, and E. Galal, "A miniaturized lowpass/bandpass filter using double arrow head defected ground structure with centered etched ellipse," Progress In Electromagnetics Research Letters, Vol. 24, 99-107, 2011.
9. Wang, C. J. and T. H. Lin, "A multi-band meandered slotted-ground-plane resonator and its application of lowpass filter," Progress In Electromagnetics Research, Vol. 120, 249-262, 2011.
10. Hayati, M., H. A.-D. Memari, and H. Abbasi, "Compact microstrip lowpass filter with sharp roll-off and wide stopband using semicircle stub resonator," Progress In Electromagnetics Research Letters, Vol. 35, 73-81, 2012.
11. Hayati, M. , H. Asadbeigi, and A. Sheikhi, "Microstrip lowpass filter with high and wide rejection band," Elecron. Lett., Vol. 48, No. 19, 1217-1219, 2012.
12. Wang, J. P., H. Cui, and G. Zhang, "Design of compact microstrip lowpass filter with ultra-wide stopband," Elecron. Lett., Vol. 48, No. 14, 854-856, 2012.
13. Hong, J. S. and M. J. Lancaster, Microstrip Filter for RF/Microwave Applications,, Wiely, New York, 2001.