Miniature directional coupling device

Differing from conventional directional coupling device being implemented on a coin-like planar board, the present invention stacks a bottom substrate, at least one phase retarding unit, at least one reference ground unit, a coupled circuit layer, a main circuit layer, and a top substrate to form a miniature directional coupling device. Because this miniature directional coupling device not occupies too much circuit area when being applied in a mobile communication product, the miniature directional coupling device can meet the requirements of light weight and compact size demanded by high-technology mobile communications for the electronic components. It is worth explaining that, since the said phase retarding unit consists of many end-to-end connected transmission wires, engineers skilled in designing microwave circuit are able to carry out the modulation of coupling flatness of the miniature directional coupling device by changing a total length of the end-to-end connected transmission wires.