A compact branch-line coupler with arbitrary power division and multi frequencies suppression

In this article, a compact uniplanar branch line coupler is designed to achieve arbitrary power division ratio and multi suppression frequencies simultaneously. By replacing conventional quarter wavelength lines with the equivalent multi T-shaped lines, the branch-line coupler could have multi frequencies suppression while maintaining the conventional performance of proposed power division ratio at the fundamental frequency. Its circuit parameters are determined by the transmission line theory, and explicit design formulas are derived by ABCD-matrix. For verification, a planar microstrip branch-line coupler is simulated, fabricated and measured. Experimental results show the suppression to be over -30 dB at 3 GHz and 4.5 GHz, while operating well at 1 GHz. The circuit area o f the prototype is only 50.4% of the conventional coupler.