A stub tapped compact hybrid coupler with broad-band harmonic rejection

This paper presents a modified, stub tapped hybrid ring coupler for broadband harmonic suppression. In the new design, a tapped stub is used to realize 900 transmission line sections of the conventional coupler. The slow wave effect and the stopband produced by shunt open stub are utilized to achieve the size reduction and harmonic suppression respectively. Explicit design equations are derived using the ABCD-matrix. A prototype coupler operating at 1.0 GHz is designed, fabricated and measured for demonstration. The circuit area of the proposed coupler is only 45.6% of that of the conventional one. In addition, the proposed coupler has spurious pass-band suppression of up to at least nine harmonics.