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90 DESIGN007 MAGAZINE I AUGUST 2020 For the past several years, I have been working with many different millimeter-wave (mmWave) applications. I have also been working more with high-speed digital (HSD) applications, and when looking at some of the data, I had become somewhat frustrated. Sometimes, the insertion loss curves gener- ated for HSD applications have a tremendous amount of noise, and the few times I inves- tigated, I found the testing results had poor return loss, and the HSD engineer was not concerned. From my mmWave background, that really disturbed me because return loss is one of the critical properties for obtaining valid data. However, as I have learned more about HSD, I find the technology is commonly focused on the time domain—and return loss has much less influence on most time-domain performance issues. With my learning curve improving for HSD—and more specifically, Utilizing mmWave Technology to Optimize High-Speed Designs very high-speed digital (vHSD)—I now see a lot of areas where understanding the tricks of mmWave technology could help improve design and performance for vHSD technology. Impedance transitions for mmWave are extremely important to characterize, and this is typically done to get the best return loss behavior for the circuit. Just as a quick side note and clarification, return loss is also some- times called reflected loss and refers to how much energy is reflected from a propagation medium. For example, the transition from the connector to the circuit usually has an imped- ance anomaly. If that is not well characterized, much of the energy that would be desired to be inserted on the circuit will get reflected back to the source due to poor return loss (reflected loss). In this case, the poor return loss is prob- ably due to the impedance transition between the connector and the circuit, and that transi- Lightning Speed Laminates by John Coonrod, ROGERS CORPORATION

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