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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 Microw. Meas. Conf., Denver, CO, USA)

   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 SIWGCPW 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. A compact F-band filter based on SiC substrate-integrated waveguides

   Wang, X. ; Asadi, M. J. ; Li, L. ; Li, T. ; Hwang, J. C. ; Thome, F. ; Brueckner, P. ; Schwantuschke, D. ( December 2023 , Asia-Pacific Microw. Conf. (APMC), Taipei, Taiwan, Dec. 2023)

   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 (GCPW). 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 high-quality 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 next-generation automobile radars. 

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4. Propagation Measurement System and Approach at 140 GHz-Moving to 6G and Above 100 GHz

   https://doi.org/10.1109/GLOCOM.2018.8647921  

   Xing, Yunchou ; Rappaport, Theodore S. ( December 2018 , 2018 IEEE Global Communications Conference (GLOBECOM))

   Abstract: With the relatively recent realization that millimeter wave frequencies are viable for mobile communications, extensive measurements and research have been conducted on frequencies from 0.5 to 100 GHz, and several global wireless standard bodies have proposed channel models for frequencies below 100 GHz. Presently, little is known about the radio channel above 100 GHz where there are much wider unused bandwidth slots available. This paper summarizes wireless communication research and activities above 100 GHz, overviews the results of previously published propagation measurements at D-band (110-170 GHz), provides the design of a 140 GHz wideband channel sounder system, and proposes indoor wideband propagation measurements and penetration measurements for common materials at 140 GHz which were not previously investigated. 

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5. Effect of Standing Wave on Terahertz Channel Model

   https://doi.org/10.1109/ICCWorkshops50388.2021.9473787  

   Tran, Ha ; Le, Thanh ; Singh, Suresh ( June 2021 , 2021 IEEE International Conference on Communications Workshops (ICC Workshops))

   null (Ed.)

   There is a growing interest in exploiting the terahertz frequency band for future communication systems that demand high data rates. Given the complex propagation behavior of this frequency band, various researchers have developed channel models that can be utilized in the development of communication systems. These models however do not include a crucial aspect of terahertz propagation at short distances – the presence of standing waves. Our measurements show that at specific distances, the effect of standing waves is significant. In this paper, we extend previous terahertz channel models to include the effect of standing waves and show a good fit with our measurements. Our measurements and modeling cover the five most promising terahertz frequency bands – 140, 220, 340, 410, 460 GHz. 

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