High-frequency circuit board and antenna module

A high-frequency circuit board comprising:

• a first insulating layer having a first dielectric constant;
• a first metal layer provided to stack over the first insulating layer;
• a second insulating layer provided to stack over the first metal layer, and having a second dielectric constant lower than the first dielectric constant;
• a second metal layer provided to stack over the second insulating layer, on which a compound semiconductor device is mounted;
• and first vias penetrating the second insulating layer and connecting the first metal layer with the second metal layer, further comprising:
• a third metal layer arranged on an opposite side to the first metal layer with respect to the first insulating layer, and held at reference potential;
• and second vias penetrating the first insulating layer and connecting the first metal layer with the third metal layer.