A circuit board comprises at least a first wiring layer, a second wiring layer and a via. The first wiring layer is formed with a pair of first ends, a pair of second ends, a coupling portion, a pair of first trace portions and a pair of second trace portions. The coupling portion has a pair of first coupling points, a pair of second coupling points, an inner trace portion, an outer trace portion and a ground conductor portion. The inner trace portion has a length equal to a length of the outer trace portion. The ground conductor portion is arranged between the inner trace portion and the outer trace portion. The second wiring layer is formed with a ground pattern. The ground conductor portion is connected with the ground pattern through the via.