A low pass filter with ultra-wide band rejection and compact size using a proposed radial loaded transformed radial stubs is introduced and investigated. The implemented unite cell low pass filter with 1-dB cutoff frequency fc of 3.2 GHz demonstrates stopband rejection up to 11.8 fc i.e. 38 GHz. The design is further extended to the high-order LPF through cell cascading. The implemented four-cell LPF with fc of 3.6 GHz demonstrated 35dB rejection from 4.8GHz to 39GHz, 50 dB rejection from 5.4 GHz to 26 GHz (7.2 fc) and 20dB rejection from 4.4 GHz to 50 GHz (13.8 fc). The measured passband insertion loss is less than 1.7 dB, and group delay is from 0.45~0.8 nS. The size of the four-cell low pass filter is only 0.33λg × 0.135λg, (λg is the guide wavelength at center cutoff frequency) without using any lumped elements.
1. 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. doi:10.1109/LMWC.2005.850479
2. Luo, S., L. Zhu, and S. Sun, "Stopband-expanded low-pass filters using microstrip coupled-line hairpin units," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 8, 506-508, Aug. 2008. doi:10.1109/LMWC.2008.2001004
3. Sheen, J.-W., "A compact semi-lumped low-pass filter for harmonics and spurious suppression," IEEE Microw. Wireless Compon. Lett., Vol. 10, No. 3, 92-93, Mar. 2000.
4. Yang, G. M., R. Jin, J. Geng, X. Huang, and G. Xiao, "Ultra-wideband bandpass filter with hybrid quasi-lumped elements and defected ground structure," IET Microw.. Antennas Propag., Vol. 1, No. 3, 733-736, Jun. 2007. doi:10.1049/iet-map:20060288
5. Chen, J., Z.-B. Weng, Y.-C. Jiao, and F.-S. Zhang, "A multi-band meandered slotted-groundplane resonator and its application of low-pass filter," Progress In Electromagnetics Research, Vol. 70, 269-280, 2007. doi:10.2528/PIER07012603
6. Wang, C.-J. and T. H. Lin, "Lowpass filter design of Hilbert curve ring defected ground structure," Progress In Electromagnetics Research, Vol. 120, 249-262, 2011.
7. March, S. L., "Analyzing lossy radial-line stubs," IEEE Trans. Microw. Theory Tech., Vol. 33, No. 3, 269-271, Mar. 1985. doi:10.1109/TMTT.1985.1132997
8. Ma, K., K. S. Yeo, and Q. Sun, "A novel planar multimode bandpass filter with Radial perturbation," Microwave and Optical Technology Letters, Vol. 51, No. 4, 964-966, Apr. 2009. doi:10.1002/mop.24258
9. Ma, K. and K. S. Yeo, "Novel low cost compact size planar low pass filters with deep skirt selectivity and wide stopband rejection," IEEE MTT-S Int. Microwave Symp. Dig., 233-236, 2010.
10. Ma, 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, Mar. 2011. doi:10.1109/TMTT.2010.2095031
11. Wu, Y., Y. Liu, S. Li, and C. Yu, "A new wide-stopband low-pass filter with generalized coupled-line circuit and analytical theory," Progress In Electromagnetics Research, Vol. 116, 553-567, 2011.
12. Ma, K., J.-G. Ma, M. A. Do, and K. S. Yeo, "Characterizing and modeling conductor-backed CPW periodic band stop filter with miniaturized size," IEEE MTT-S Int. Microwave Symp. Dig., 983-986, 2007.