Compact cascaded branch line coupler using T-sections conversion

The branch line coupler has many applications such as phase shifters, vector modulators, amplifiers and mixers and etc. The conventional branch line coupler consists of four arms each have μ/4 length with different impedances. To broaden the bandwidth, the couplers need to be cascaded, but due to the cascading, the overall size will be very large. To minimize the overall size, a T-section conversion was used instead of each of the quarter wave length arms. The new cascaded coupler occupies 33.5% of the area needed for the conventional cascaded coupler. Added to the size reduction, the new cascaded branch line coupler has nearly the same frequency response and fractional bandwidth as the conventional cascaded branch line coupler.