Miniaturization design of 3dB directional coupler applied to balanced power amplifier in WLAN system

Abstract

This paper designs a 3dB branch line coupler which is applied to the balanced power amplifier. By the traditional meandering method, the microstrips of the branch line coupler are bended to inside, thereby the size of the structure is reduced. The size of optimized branch line coupler is 0.18λ×0.13λ. Test results show that, in the 2.4∼2.485 GHz band, the magnitude of the straight port is consistent with that of the coupling port, and the phase difference can be 90 degree. Also, the isolation degree is greater than 15dB.