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66 DESIGN007 MAGAZINE I APRIL 2022 Over the past several years there has been a steady increase in millimeter-wave (mmWave) applications. is was probably sparked by the chip industry, which has the capability to produce chips in large volume that have good mmWave performance. As the mmWave appli- cations increased, most aspects of the electron- ics industry, including the PCB industry, were forced into a steep learning curve. As a general statement, the quality of the circuit board is more critical to mmWave applications as com- pared to lower frequency applications. To be more specific, the quality concerns are mostly related to consistency of circuit features such as conductor widths, conductor shapes, con- ductor spacing, substrate thickness, copper thickness, and final plated finishes. Millimeter-wave applications are more sen- sitive to circuit features, due to wavelength. Wavelength is the physical length of a propa- gating wave and, as an example, the physi- cal length of a wave at 3.3 GHz is about 2.3 inches. at is assuming a microstrip built on a thin laminate with a Dk of approximately 3.0. Within that 2.3 inches, the wave is made up of 360 degrees, which is also referred to as phase angles. If the propagating wave encounters an anomaly which is 0.023" in size, this is the same thing as 1% of the wavelength or about 3.6 degrees. is small anomaly, in relation to the wavelength, will have very little effect on the propagating wave. However, at a mmWave frequency, such as 77 GHz, the physical length of the wave is about 0.095" and if the same The Importance of Circuit Features for Millimeter-Wave Applications Lightning Speed Laminates by John Coonrod, ROGERS CORPORATION

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