Miniaturized quasi-asymmetric forward-wave coupled-line coupler with arbitrary coupling level

A design method is demonstrated for quasi-asymmetric forward-wave coupled-line couplers. By loading a symmetric coupled line asymmetrically with shunt capacitors, a miniaturized forward-wave coupler is constructed with an arbitrary maximum coupling level. Most importantly, elimination of lengthy impedance transformers makes the method the most effective miniaturization method. Experimental results are provided for a 3-dB coupler with a miniaturization rate of 92.9% at 5 GHz.