This paper presents a monolithic 3D printed twisted waveguide bandpass filter. The component integrates filtering and polarization rotation functionalities. It operates with a center frequency of 60 GHz and a fractional bandwidth (FBW) of 5%. The filter was made from stainless steel using micro laser sintering (MLS) process. It was designed and printed in such a way that no internal support structures are required. The measured response of the as-printed filter showed a very decent frequency response with a minimum insertion loss of 1.3 dB and a return loss better than 18.7 dB without any tuning. The filter was then gold coated using electroless process which significantly improved the insertion loss to a minimum of 0.3 dB. The results demonstrate the capability of the high-precision 3D metal printing technology in fabricating complex geometries that are challenging using conventional milling techniques, as well as an effective plating technique.

We report a $D$ -band waveguide diplexer, with two passbands of 130–134 and 151.5–155.5 GHz, fabricated using micro laser sintering (MLS) additive manufacturing with stainless steel. This is the first demonstration of metal 3-D printing technology for multiport filtering devices at a sub-terahertz (THz) frequency. For comparison, the same diplexer design has also been implemented using computer numerical controlled (CNC) milling. The diplexer, designed using coupling matrix theory, employs an all-resonator and $E$ -plane split-block structure. The two channels are folded for compactness. A staircase coupled structure is used in one channel to increase the isolation performance. The printed waveguide flanges are modified to adapt to the limited printing volume from the MLS. Effects of fabrication tolerance on the diplexer are investigated. An effective and unconventional electroless plating process is developed. The measured average insertion losses of the gold-coated diplexer are 1.31 and 1.37 dB, respectively. The respective frequency shifts from design values are 0.92% and 1.1%, and bandwidth variations are 4% and 15%. From a comprehensive treatment of the end-to-end manufacturing process, the work demonstrates MLS to be a promising fabrication technique for complex waveguide devices at a sub-THz frequency range.

This article explored the use of high-precision metal three-dimensional printing in subterahertz waveguide devices and demonstrated a 300 GHz waveguide bandpass filter made by micro laser sintering (MLS) process. The filter structure is composed of five rectangular waveguide cavities (fundamental TE 101 mode), two back-to-back right-angle bends and WR-03 waveguide sections. It is made of two identical blocks of stainless steel and two brass plates were used to clamp them together and achieve secure contact in the E plane cut. The measured response of the as fabricated stainless-steel filter showed minimum passband insertion loss of 4.7 dB due to the degraded effective conductivity of the stainless steel and surface roughness. To reduce the insertion loss, the filter was gold plated using an electro-less process with nickel undercoat layer. Plating the filter significantly improved the passband insertion loss, measured to be between 1.1 and 2.7 dB. Inspection of the filter using an Alicona optical system showed that dimensional accuracy within ± 15 μm on average has been achieved by the MLS printer. The investigative study tested the boundary of the technology in subterahertz device applications.

This paper presents a fifth-order waveguide bandpass filter fabricated by 3D printing technology. The filter has a centre frequency of 180 GHz, a fractional bandwidth FBW=11% and a Chebyshev filtering response. The filter is fabricated by the micro laser sintering process and it is made as an all-metal monolithic device. Two samples of the specified filter are made of stainless steel and tested. The measured results are encouraging and demonstrate the excellent reproducibility of the fabrication process.

This brief presents a fifth-order W-band waveguide bandpass filter with a Chebyshev response, operating at center frequency of 90 GHz and having fractional bandwidth of 11%. The filter is fabricated by micro laser sintering process which is a powder bed based additive manufacturing technology. Use of this technology allows the filter to be made accurately with high resolution and good surface quality in one piece. This results in better performance in term of insertion loss and reproducibility. For the purpose of comparison, two similar filters are presented in this brief with the same structure and specification, one made from stainless steel and the other made from stainless steel coated with copper. Both filters are tested and have excellent agreement between measurements and simulations.

This paper presents reproducibility and quality assessment of two identical 90 GHz micro laser sintered waveguide bandpass filters. Both filters operating at center frequency of 90 GHz, with bandwidth of 10 GHz and return loss of 20 dB. The filters are fabricated by micro laser sintering process which is a metal 3-D printing technique, allowing the components to be fabricated in a single piece with high resolution and good surface quality accurately. This paper shows that micro laser sintering can be used to reproduce high frequency filters repeatedly with almost identical responses. The micro laser sintering process can provide reproducibility for small to medium batch size production of high frequency components. The paper discusses the quality of both filters by comparing the measured results with simulated results and providing the surface roughness measurements. Both filters are tested, and measurement results have excellent agreement with simulated results.