A 10dB Branch Line Coupler Using Defected Ground Structure

This paper presents a novel 90° branch-line coupler with DGS(Defected Ground Structure), which is etched on the backside metallic plane. The DGS section can implement high impedance transmission line easily with microstrip configuration. DGS sections under a conventional microstrip line are analyzed to find the characteristic impedance and electrical length by means of three dimensional field analysis. In order to show the validity of the proposed DGS section, a branch-line coupler with the loose coupling of lOdB is fabricated and measured. Measured performances of lOdB branch line coupler with DGS show excellent agreement with predicted results.