A Compact Via-less Ultra-Wideband Microstrip Filter by Utilizing Open-Circuit Quarter Wavelength Stubs

Authors: Muhammad Yasir Wadood, Fatemeh Babaeian

Abstract:

By developing ultra-wideband (UWB) systems, there is a high demand for UWB filters with low insertion loss, wide bandwidth, and having a planar structure which is compatible with other components of the UWB system. A microstrip interdigital filter is a great option for designing UWB filters. However, the presence of via holes in this structure creates difficulties in the fabrication procedure of the filter. Especially in the higher frequency band, any misalignment of the drilled via hole with the Microstrip stubs causes large errors in the measurement results compared to the desired results. Moreover, in this case (high-frequency designs), the line width of the stubs are very narrow, so highly precise small via holes are required to be implemented, which increases the cost of fabrication significantly. Also, in this case, there is a risk of having fabrication errors. To combat this issue, in this paper, a via-less UWB microstrip filter is proposed which is designed based on a modification of a conventional inter-digital bandpass filter. The novel approaches in this filter design are 1) replacement of each via hole with a quarter-wavelength open circuit stub to avoid the complexity of manufacturing, 2) using a bend structure to reduce the unwanted coupling effects and 3) minimising the size. Using the proposed structure, a UWB filter operating in the frequency band of 3.9-6.6 GHz (1-dB bandwidth) is designed and fabricated. The promising results of the simulation and measurement are presented in this paper. The selected substrate for these designs was Rogers RO4003 with a thickness of 20 mils. This is a common substrate in most of the industrial projects. The compact size of the proposed filter is highly beneficial for applications which require a very miniature size of hardware.

Keywords: Band-pass filters, inter-digital filter, microstrip, via-less.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.2643704

References:

[1] F. C. Commission, "Revision of part 15 of the commission's rules regarding ultra-wideband transmission systems," First report and order, pp. FCC 02-48, 2002.
[2] W. Chen, X. Guo, B. Cao, X. Zhang, B. Wei, Y. Zhang, et al., "A superconducting microstrip ultra-wideband (UWB) bandpass filter at VHF-band," IEEE Microwave and Wireless Components Letters, vol. 19, pp. 635-637, 2009.
[3] C.-L. Hsu, F.-C. Hsu, and J.-K. Kuo, "Microstrip bandpass filters for ultra-wideband (UWB) wireless communications," in IEEE MTT-S International Microwave Symposium Digest, 2005, 2005, pp. 4 pp.-682.
[4] C.-W. Tang and M.-G. Chen, "A microstrip ultra-wideband bandpass filter with cascaded broadband bandpass and bandstop filters," IEEE Transactions on microwave theory and techniques, vol. 55, pp. 2412-2418, 2007.
[5] C.-H. Wu, Y.-S. Lin, C.-H. Wang, and C. H. Chen, "A compact LTCC ultra-wideband bandpass filter using semi-lumped parallel-resonance circuits for spurious suppression," in 2007 European Microwave Conference, 2007, pp. 532-535.
[6] L. Zhu, S. Sun, and R. Li, Microwave bandpass filters for wideband communications vol. 232: John Wiley & Sons, 2011.
[7] M. Hajebi, E. Zarezadeh, and F. Babaeian, "A Compact Ultra-Wideband Filter Based on Left Handed Transmission Line by Using Complementary Split Ring Resonators and Series Capacitor," Journal of Communication Engineering, vol. 4, pp. 111-121, 2015.
[8] C. P. Chen, H. Nihei, Z. Ma, and T. Anada, "Synthesis of compact UWB bandpass filter with improved performances," Microwave and Optical Technology Letters, vol. 52, pp. 1268-1271, 2010.
[9] P. Khare, "Design and analysis of a 5-pole interdigital band-pass filter at 2.4 GHz," in 2015 International Conference on Communication Networks (ICCN), 2015, pp. 93-96.
[10] X. Jia, Y. Na, S. Bingxia, and Z. Quanming, "The miniaturization design of microstrip interdigital bandpass filter," in 2009 2nd International Conference on Power Electronics and Intelligent Transportation System (PEITS), 2009, pp. 74-76.
[11] J. Zhu, Y. Yu, N. Yang, B. Zhou, and Y. Zhang, "Micromachined silicon via-holes and interdigital bandpass filters," MEMS, Systems for Information Processing and Storage, vol. 12, pp. 913-917, 2006.
[12] Babaeian, F. and N. C. Karmakar (2018). "A High Gain Dual Polarized Ultra-Wideband Array of Antenna for Chipless RFID Applications." IEEE Access 6: 73702-73712.