Patent ID: 8462074

Claim:
A planar antenna, disposed on a plate having a first surface and a second surface, the planar antenna comprising: a metal layer, disposed on the first surface, and having a slot line for exposing the first surface; an antenna body, disposed on the second surface, and having a ground end and a feed end; a coupling device, disposed on the second surface, and a partial area of the coupling device corresponding to the slot line of the metal layer; a matching device, disposed on the second surface and electrically connected to the coupling device and the feed end; and a stepped impedance device, disposed on the second surface, and comprises: a first impedance wire, having a first impedance Z 1 , and a distance between two ends thereof being D 1 ; and a second impedance wire, having one end electrically connected to the first impedance wire and another end electrically connected to the ground end of the antenna body, and having a second impedance Z 2 , and a distance between two ends thereof being D 2 , wherein when λ 1 is a first wavelength, θ 1 is a first phase angle, and r is a positive number, the aforementioned D 1 , D 2 , Z 1 and Z 2 are in accord with following equations: tan θ 1 ×tan( r·θ 1 )= Z 1 /Z 2 ,D 1 =(θ 1 ×λ 1 )/360 and D 2 =r×D 1 .