Wiring board and vehicle display device

A wiring board comprising:

• a wiring layer provided on a first surface of an insulating substrate having a predetermined thickness, and a flat shape;
• and
• a ground plane provided on a second surface that opposes the first surface via the insulating substrate;
• wherein
• the wiring layer includes
• a signal transmission pattern serving as a transmission path that transmits a high-frequency signal,
• a first ground pattern serving as a first ground surface that defines a reference potential in the wiring board, and
• a second ground pattern serving as a second ground surface that is DC-isolated from the first ground pattern, and which functions as an AC ground for an AC signal flowing through the signal transmission pattern, the second ground pattern including a ground pattern for an electronic component, the ground pattern for an electronic component being connected to another pole of an electronic component that is mounted as a result of one pole being connected to the signal transmission pattern,
• the ground plane is formed with
• a first cutout portion, being a cutout portion for the electronic component, which is formed at a position facing the electronic component mounted on the wiring layer via the insulating substrate, and in which a conductor layer constituting the second ground pattern is removed, and
• a second cutout portion serving as a slit portion that electrically isolates a first ground plane corresponding to the first ground pattern of the wiring layer and a second ground plane corresponding to the second ground pattern of the wiring layer,
• in a transparent plan view as viewed from the first surface side of the insulating substrate, the first and second cutout portions are arranged such that at least a portion is overlapping,
• in a transparent plan view as viewed from the first surface side of the insulating substrate, the ground pattern for an electronic component included in the second ground pattern extends in a transmission direction of the AC signal across the second cutout portion serving as the slit portion,
• the first ground plane is electrically connected to the ground pattern for an electronic component by a first through-conductor that penetrates through the insulating substrate,
• the second ground plane is electrically connected to the ground pattern for an electronic component by a second through-conductor that penetrates through the insulating substrate, and
• the first through-conductor, the ground pattern for an electronic component, and the second through-conductor constitute a bypass path that causes a return current, which is generated in the ground pattern in response to the AC signal flowing in the signal transmission path, to flow around the second cutout portion serving as the slit portion.