Miniaturization and harmonic suppression of branch-line and rat-race hybrid coupler using compensated spiral compact microstrip resonant cell

In this paper, a compensated spiral compact microstrip resonant cell (SCMRC) is applied to design a miniaturized microstrip rat-race and branch-line hybrid coupler. The proposed structures can achieve both a significant reduction of size and harmonic suppression. As the SCMRC are constructed entirely from microstrip lines, the couplers are easily fabricated using conventional printed-circuit board fabrication process. The proposed rat-race coupler occupies only 30% of conventional one's area, while the area of the branch-line coupler with the compensated SCMRC is 24% of the conventional case. On the other hand, the performance of the proposed couplers is as good as that of the corresponding conventional structures and deep harmonic suppression in addition. The design and simulation have been performed using full-wave analysis based on ADS Momentum.