Post-wall waveguide based short slot directional coupler, butler matrix using the same and automotive radar antenna

A short slot directional coupler comprising:

• a dielectric substrate having both surfaces each covered by a metal film;
• a first via-hole string and a second via-hole string, each of which has via-holes penetrating through the substrate, and formed so that a distance between the first via-hole string and the second via-hole string is narrow at a center of the string and wider along directions of both ends of the string;
• and
• a pair of third via-hole strings each having via-holes penetrating through the substrate, and formed between parts adjacent to both ends of the first via-hole string and parts adjacent to both ends of the second via-hole string to form a first post-wall waveguide along with the first via-hole string and a second post-wall waveguide along with the second via-hole string, wherein the first post wall waveguide, the second post wall waveguide and third post waveguides defined by the first via-hole string and the second via-hole string vary in width in multi-stepped form.

A short slot directional coupler comprising:

• a first dielectric substrate and a second dielectric substrate whose one-side surfaces are opposed to each other and whose other-side surfaces each are covered by a metal film;
• an intermediate dielectric layer interposed between the one-side surfaces of the first dielectric substrate and the second dielectric substrate;
• a first via-hole string and a second via-hole string each having via-holes penetrating through the first dielectric substrate and the second dielectric substrate, and formed so that a distance between the first via-hole string and the second via-hole string is narrow at a center of the string along a length direction thereof and wider along directions of both ends of the string;
• and
• a pair of third via-hole strings each having via-holes penetrating through the first dielectric substrate, the intermediate dielectric layer and the second dielectric substrate, and formed between parts adjacent to both ends of the first via-hole string and parts adjacent to both ends of the second via-hole string to form a first post-wall waveguide along with the first via-hole string and a second post-wall waveguide along with the second via-hole string,
• wherein each via-hole interval in the first via-hole string, the second via-hole string and the third via-hole string is set to a value not more than 90% in an area on which each width of the first post-wall waveguide, the second post-wall waveguide and third post wall waveguides defined by the first via-hole string and the second via-hole string satisfies a following equation:
• w
• >
• 1
• f
• 0
• ⁢
• c
• ɛ
• r
• where f0 represents an operating frequency, ∈r represents a relative conductivity of the substrate, and c represents a light velocity.