There is an episode about a type of high DK microwave PCB ---- RT/duroid 6010.2LM PCB.

Rogers RT/duroid 6010.2LM high frequency PCBs are a type of high DK PCB boards of ceramic-filled PTFE composites which are designed for electronic and microwave circuit applications.

High dielectric constant material can reduce the size of microwave circuits because it requires narrower conductors for controlled impedance. It will make the resonator shorter and the overall filters smaller.

The dielectric constant of RT/duroid 6010.2LM is as high as 10.2 and dissipation factor is as low as 0.0023 at 10 GHz. It's well suited for electronic and microwave circuit applications requiring a high dielectric constant. The low loss is ideal for operating at X-band or below.

The thermal coefficient of dielectric constant is -425 ppm/℃ due to its filling ceramics.

The moisture absorption is as low as 0.01%. This helps to reduce effects of moisture on electrical loss. RT/duroid 1060.2LM also has good thermal mechanical stability because of the ceramic fillers, its thermal conductivity is as high as 0.86 W/mK.

The coefficient of thermal expansion on X and Y axis is similar to copper, and Z-axis CTE is as low as 47 ppm/℃, this property ensures the reliable plated through-holes in multi-layer boards.