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1. Single-Sweep vs. Banded Characterizations of a D-band Ultra-Low-Loss SiC Substrate-Integrated Waveguide

   Li, L.; Reyes, S.; Asadi, M. J.; Jena, D.; Xing, H. G.; Fay, P.; Hwang, J. C. (June 2022, ARFTG Microwave Measurement Conference)

   A D-band (110‒170 GHz) SiC substrate-integrated waveguide (SIW) is characterized on-wafer by two different vector network analyzers (VNAs): a 220-GHz single-sweep VNA and an 110-GHz VNA with WR8 (90‒140 GHz) and WR5 (140‒220 GHz) frequency extenders. To facilitate probing, the SIW input and output are transitioned to grounded coplanar waveguides (GCPWs). Two-tier calibration is used to de-embed the SIW-GCPW transitions as well as to extract the intrinsic SIW characteristics. In general, the two VNAs are in agreement and both result in an ultra-low insertion loss of approximately 0.2 dB/mm for the same SIW, despite stitching errors at band edges. 

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2. Sub-terahertz devices and test metrology

   Li, L.; Asadi, M. J.; Li, T.; Wang, X.; Hwang, J. C. (September 2023, SRC TECHCON, Autsin, TX, Sep. 2023)

   As 6G wireless communications push the operation frequency above 110 GHz, it is critical to have low-loss interconnects that can be accurately tested. To this end, D-band (110 GHz to 170 GHz) substrate-integrated waveguides (SIWs) are designed on a 100-μm-thick SiC substrate. The fabricated SIWs are probed on-wafer in a single sweep from 70 kHz to 220 GHz with their input/output transitioned to grounded coplanar waveguides (GCPWs). From CPW-probed scattering parameters, two-tier calibration is used to de-embed the SIW-GCPW transitions and to extract the intrinsic SIW characteristics. In general, the record low loss measured agrees with that obtained from finite-element full-wave electromagnetic simulation. For example, across the D band, the average insertion loss is approximately 0.2 dB/mm, which is several times better than that of coplanar or microstrip transmission lines fabricated on the same substrate. A 3-pole filter exhibits a 1-dB insertion loss at 135 GHz with 20-dB selectivity and 11% bandwidth, which is order-of-magnitude better than typical on-chip filters. These results underscore the potential of using SIWs to interconnect transistors, filters, antennas, and other circuit elements on the same monolithically integrated chip. 

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3. Sub-terahertz devices and test metrology

   Li, Lei; Asadi, Mohammad J; Li, Tianze; Wang, Xiaopeng; Hwang, James CM (September 2023, ARGTEG Measurement Conference)

   As 6G wireless communications push the operation frequency above 110 GHz, it is critical to have low-loss interconnects that can be accurately tested. To this end, D-band (110 GHz to 170 GHz) substrate-integrated waveguides (SIWs) are designed on a 100-μm-thick SiC substrate. The fabricated SIWs are probed on-wafer in a single sweep from 70 kHz to 220 GHz with their input/output transitioned to grounded coplanar waveguides (GCPWs). From CPW-probed scattering parameters, two-tier calibration is used to de-embed the SIW-GCPW transitions and to extract the intrinsic SIW characteristics. In general, the record low loss measured agrees with that obtained from finite-element full-wave electromagnetic simulation. For example, across the D band, the average insertion loss is approximately 0.2 dB/mm, which is several times better than that of coplanar or microstrip transmission lines fabricated on the same substrate. A 3-pole filter exhibits a 1-dB insertion loss at 135 GHz with 20-dB selectivity and 11% bandwidth, which is order-of-magnitude better than typical on-chip filters. These results underscore the potential of using SIWs to interconnect transistors, filters, antennas, and other circuit elements on the same monolithically integrated chip. 

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4. High Power Characterization of SIW-based D-band Traveling Wave Amplifiers

   Wu, Weifeng; Li, Lei; Hwang, James_C_M; Fay, Patrick (September 2025, European Microwave Conference, 2025)

   The high-power performance of a D-band (110–170 GHz) traveling wave amplifier (TWA) is reported. The amplifier was designed and fabricated using a GaN-on-SiC high-electron mobility transistor (HEMT) technology integrated with a substrate integrated waveguide (SIW) structure for low-loss on-chip power combining. Active injection load-pull measurements of both discrete HEMTs as well as the completed MMIC TWA were performed. The discrete HEMT measurements at D-band supplement the available design data for these scaled GaN HEMTs. The TWA achieved a peak power-added efficiency (PAE) of 9.1% at 145 GHz. The available output power exceeded 23.5 dBm from 135-145 GHz, with a maximum output power of 24.7 dBm (295 mW) at 140 GHz. Keywords—millimeter 

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5. A Compact F-band Filter Based on SiC Substrate-integrated Waveguides

   https://doi.org/10.1109/APMC57107.2023.10439892  

   Wang, Xiaopeng; Asadi, Mohammad Javad; Li, Lei; Li, Tianze; Hwang, James_C M; Thome, Fabian; Brückner, Peter; Schwantuschke, Dirk (December 2023, IEEE)

   F-band substrate-integrated waveguides (SIWs) are designed, fabricated, and characterized on a SiC wafer, along with SIW-based filters, impedance standards, and transitions to grounded coplanar waveguides (GCPWs). The GCPW-SIW transitions not only facilitate wafer probing, but also double as resonators to form a 3-pole band-pass filter together with an SIW resonator. The resulted filter exhibits a 1.5-dB insertion loss at 115 GHz with a 34-dB return loss and a 19-GHz (16%) 3-dB bandwidth. The size of the filter is only 63% of previous filters comprising three SIW resonators. These results show the feasibility for monolithic integration of highquality filters with high-efficiency antennas and amplifiers in a single-chip RF frontend above 110 GHz, which is particularly advantageous for 6G wireless communications and nextgeneration automobile radars. 

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