Design of a compact branch line coupler with harmonic suppression using T-shaped lines and open stubs for wireless applications

In this paper a novel branch line coupler with harmonic suppression and size reduction is designed. The proposed coupler is designed by using T-shaped lines, cross lines and open ended stubs. The presented coupler is designed at the operating frequency of 1.8 GHz, which can suppress up to fifth harmonic. Moreover, more than 78.5% size reduction is achieved, compared to the conventional coupler. In the other words the proposed coupler suppresses second, third, fourth and fifth harmonics with more than 15 dB, 27 dB, 24 dB, and 21 dB attenuation levels, respectively. The obtained insertion loss is less than 0.05 dB for both output ports. In addition, more than 28.3 dB and 27.9 dB return loss and output port isolation are obtained respectively. The designed coupler has a wide operating band from 1.67 GHz up to 1.93 GHz with center frequency of 1.8 GHz which shows 15% fractional bandwidth (FBW).