A 3-D printed bandpass filter using tm-mode slotted spherical resonators with enhanced spurious suppression

Fan Zhang, Cheng Guo, Yi Zhang, Yang Gao, Bing Liu, Minjie Shu, Yi Wang, Yuliang Dong, Michael J. Lancaster, Jun Xu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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This article presents a Ka-band fourth-order slotted spherical resonator waveguide bandpass filter (BPF) with a wide spurious suppression stopband. It uses the first higher-order TM211 mode rather than the fundamental TM101 mode of the spherical resonator in order to obtain a higher unload quality factor (Qu) for smaller in-band insertion loss, as well as a larger filter volume that gives better tolerance to fabrication errors in high frequency applications. By introducing slots that interrupt surface currents, the fundamental TM101 and two higher spurious modes (TE101 and TM311) can be suppressed without compromising the unloaded quality factor of the TM211 mode. In addition, the filter topology is optimized to further enhance the suppression level of the spurious passbands. A Z-shaped topology has been found effective in decreasing the coupling strength of the spurious TM311 mode. An analysis is performed to demonstrate the better tolerance of the Z-shaped filter over the conventional TM101-mode spherical resonator filter. For verification, a fourth-order slotted spherical resonator waveguide BPF with a center frequency of 31 GHz and bandwidth of 880 MHz is designed and manufactured using a selective laser melting (SLM) 3-D printing process. The measured results show an average in-band insertion loss of 1.53 dB, and a passband return loss better than 13.6 dB. The stopband of the filter is extended up to 40.9 GHz with a rejection level greater than 20 dB.

Original languageEnglish
Pages (from-to)213215-213223
JournalIEEE Access
Publication statusPublished - 24 Nov 2020

Bibliographical note

Funding Information: This work was supported in part by the National Natural Science Foundation of China under Grant 62001367, and in part by the U.K. Engineering and Physical Science Research Council under Contract EP/S013113/1. The work of Fan Zhang was supported in part by the China Scholarship Council through the State Scholarship Fund.


  • 3-D printed
  • Bandpass filter
  • selective laser melting
  • slotted spherical resonator
  • spurious suppression
  • TM

ASJC Scopus subject areas

  • Computer Science(all)
  • Materials Science(all)
  • Engineering(all)


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