Low dielectric loss (tanδ)
Crucially, mmWave substrates require low dissipation factor (tanδ, or loss tangent) materials, so less energy from high frequency waves passing through is lost in the substrate material. Circuit designers can work around high dielectric constants, but will find it much more difficult to work with materials that dissipate significant electromagnetic energy at the high frequencies of mmWave.
As part of the 5G/6G MAESTRO project, work on this page is supported by the Office of Advanced Manufacturing in the National Institute of Standards and Technology (NIST), under the Federal Award ID Number 70NANB22H050.