3-D printed slotted spherical resonator bandpass filters with spurious suppression

Fan Zhang, Sufang Gao, Jin Li, Yang Yu, Cheng Guo, Sheng Li, Moataz Attallah, Xiaobang Shang, Yi Wang, Michael J. Lancaster, Jun Xu

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)
245 Downloads (Pure)


In this paper, a third-order waveguide bandpass filter (BPF) based on slotted spherical resonators with a wide spurious-free stopband is presented. The resonator consists of a spherical cavity with slots opened at the top and bottom. Compared with a non-slotted spherical resonator, the slotted resonator suppresses the two spurious modes (TM211 and TE101) whilst maintaining the fundamental TM101 mode. The unloaded quality factor of the TM101 mode is not significantly degraded. This is achieved by interrupting surface current and radiating the unwanted spurious modes with the slots. The BPF is designed at a center frequency of 10 GHz with a fractional bandwidth of 1%. Two filter prototypes are fabricated, one using metal-based selective laser melting (SLM) and the other by polymer-based stereolithography apparatus (SLA) techniques. The slots also facilitate the copper electroplating process for the SLA-printed filter. The measured results show that the average passband insertion losses of the SLM- and SLA-printed filters are 0.33 and 0.2 dB, respectively. The corresponding passband return losses are better than 22 and 20 dB. The filters demonstrate excellent passband performance and wide spurious-free stopbands up to 16 GHz with stopband rejections of over 20 dB.
Original languageEnglish
Pages (from-to)128026-128034
Number of pages9
JournalIEEE Access
Early online date2 Sept 2019
Publication statusPublished - 20 Sept 2019


  • Bandpass filter
  • selective laser melting
  • slotted spherical resonator
  • spurious suppression
  • stereolithography apparatus
  • 3-D printing


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