Patent ID: 8022880

Claim:
A coupling device for transmitting a circular polarized wireless signal, comprising: a substrate, comprising a first surface and a second surface, wherein the first surface is opposite to the second surface; a ground layer, disposed on the second surface, wherein the ground layer has a circular opening, and the circular opening has an opening edge and an opening center; and a feed conductor, extending on the first surface, wherein the feed conductor comprises a conductive portion and a feed portion, the conductive portion is connected to the feed portion, and the feed portion corresponds to the circular opening, and the opening center is on a base line, the conductive portion extends parallel to the base line, a radial line is formed between the opening center and the opening edge, a radial distance is formed on the radial line between the opening edge and the feed portion, and a length of the radial distance varies with an angle between the radial line and the base line, wherein when the angle between the radial line and the base line varies in a counterclockwise direction, the radial distance increases; and wherein the feed portion comprises a first edge curve C 1 and a second edge curve C 2 , and the first edge curve C 1 and the second edge curve C 2 satisfy the following functions: C 1 ⁢ : ⁢ ⁢ ρ = D 2 ⁢ ⅇ - α ⁢ ⁢ ϕ , ( 1 ) C 2 ⁢ : ⁢ ⁢ ρ = ( D 2 - t ) ⁢ ⅇ - β ⁢ ⁢ ϕ , ( 2 ) wherein D is a diameter of the circular opening, α is a spiral rate coefficient of the first edge curve C 1 , β is a spiral rate coefficient of the second edge curve C 2 , and t is an initial thickness of the feed portion.