Highly Selective Lowpass Filter with Wide Stopband in Suspended Stripline Technology for Millimeter-wave Diplexer Applications

Document Type : Research Article


1 Communication Department, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran

2 Communication Department, Alumnus of Electrical and Computer Engineering, Shiraz University, Shiraz, Iran


This paper presents a low loss and high selective lowpass filter which is implemented using suspended stripline (SSL) technology. The proposed structure is comprised of a 13th order generalized Chebyshev lowpass filter which enjoys integrated waveguide-to-SSL transitions. This filter is designed and fabricated to be used as lowpass channel of a U-band diplexer employed in frontend of a U-band down converter. Designed filter has cut-off frequency of 50 GHz with high performance out-of-band rejection and wide stopband associated with stepped-impedance resonators realized using generalized Chebyshev prototype. Final design of filter is analyzed and optimized using 3D full-wave simulator. Filter circuit is realized on one side of a 0.127 mm-thick TLY5 substrate with dielectric constant of 2.2, which is suspended symmetrically in a waveguide channel with height of 0.961 mm and maximum width of 2 mm. Higher order modes propagation effects on filter performance are investigated to have proper single mode operation. In addition, parametric study of SSL is done to predict probable malfunctioning due to misalignment or other fabrication and packaging errors. Measurement results also are presented to verify performance of filter. The filter displays a maximum passband insertion loss of 2 dB and a return loss of better than 10 dB over the passband. Band-edge steepness reaches over 50 dB at 5 GHz away from cut-off and out-of-band rejection is higher than 45 dB at entire stopband, which are in good agreement with simulation.


Main Subjects

[1] B. Rupakula, A. Nafe, S. Zihir, Y. Wang, T.-W. Lin, G. Rebeiz, 63.5–65.5-GHz Transmit/Receive Phased-Array Communication Link With 0.5–2 Gb/s at 100–800 m and±50 Scan Angles, IEEE Transactions on Microwave Theory and Techniques, 66(9) (2018) 4108-4120.
[2] M.J. Horst, M.T. Ghasr, R. Zoughi, Design of a Compact V-Band Transceiver and Antenna for Millimeter-Wave Imaging Systems, IEEE Transactions on Instrumentation and Measurement,  (2019).
[3] A. Mirbeik-Sabzevari, S. Li, E. Garay, H.-T. Nguyen, H. Wang, N. Tavassolian, Synthetic ultra-high-resolution millimeter-wave imaging for skin cancer detection, IEEE Transactions on Biomedical Engineering, 66(1) (2018) 61-71.
[4] A.F. Elshafey, M.A. Abdalla, Low Loss High Power Air Suspended Stripline Power Divider for High Power Division Sub-Systems Applications, Progress In Electromagnetics Research, 73 (2018) 153-162.
[5] J. Sorocki, I. Piekarz, S. Gruszczynski, K. Wincza, J. Papapolymerou, Application of 3D Printing Technology for the Realization of High-Performance Directional Couplers in Suspended Stripline Technique, IEEE Transactions on Components, Packaging and Manufacturing Technology,  (2019).
[6] N.B.M. Najib, N. Somjit, I. Hunter, Design and characterisation of dual-mode suspended-substrate stripline filter, IET Microwaves, Antennas & Propagation, 12(9) (2018) 1526-1531.
[7] L. Song, B. Wu, L. Xia, Y. Guo, J. Chen, T. Su, Compact tunable cavity filter with high selectivity using double‐layer suspended stripline resonator, Microwave and Optical Technology Letters, 61(5) (2019) 1177-1180.
[8] M. Assaf, A. Malki, A.A. Sarhan, Synthesis and Design of MMR-Based Ultra-Wideband (UWB) Band Pass Filter (BPF) in Suspended Stripline (SSL) Technology, Progress In Electromagnetics Research, 84 (2019) 123-130.
[9] Z. Xu, Y. Hu, Y.P. Chen, K. Kang, J. Le Wei Li, A suspended stripline bandpass filter using hybrid transmission line stepped impedance resonator, Microwave and optical technology letters, 58(4) (2016) 892-895.
[10] J. McDaniel, J.B. Yan, P. Gogineni, Super‐wideband cascaded bandpass filter using suspended substrate stripline technology, Microwave and Optical Technology Letters, 61(6) (2019) 1491-1499.
[11] Z.-X. Xu, X. Yu, J.-Q. Liu, O.K. KS, J.L.-W. Li, Suspended stripline UWB bandpass filter with adjustable transmission zero, in:  2014 Asia-Pacific Microwave Conference, IEEE, 2014, pp. 929-931.
[12] M.H. Ho, W. Hong, L.J. Lin, Low‐pass filter of suspended stripline design with finite transmission zeros for stop‐band rejection improvement, Microwave and Optical Technology Letters, 56(2) (2014) 297-301.
[13] I. Ashiq, A. Khanna, Ultra-broadband contiguous planar DC-35–65 GHz diplexer using softboard suspended stripline technology, in:  2013 IEEE MTT-S International Microwave Symposium Digest (MTT), IEEE, 2013, pp. 1-4.
[14] I. Ashiq, A. Khanna, A novel planar contiguous diplexer DC-67-100 GHz using Organic Liquid Crystal Polymer (LCP), in:  2015 IEEE MTT-S International Microwave Symposium, IEEE, 2015, pp. 1-4.
[15] S.A. Alseyab, A novel class of generalized Chebyshev low-pass prototype for suspended substrate stripline filters, IEEE Transactions on Microwave Theory and Techniques, 30(9) (1982) 1341-1347.
[16] J.D. Rhodes, S. Alseyab, The generalized chebyshev low‐pass prototype filter, International Journal of Circuit Theory and Applications, 8(2) (1980) 113-125.
[17] S.M. Miri, K. Mohammadpour-Aghdam, S.O. Miri, A Millimeter-wave High Selective Lowpass Filter in Suspended Stripline Technology, in:  2018 Fifth International Conference on Millimeter-Wave and Terahertz Technologies (MMWaTT), IEEE, 2018, pp. 12-15.