Dual-Band Coupled-Line Couplers With Wide Separation Between Bands

In this paper, we developed three designs of dualband coupled-line couplers with wide separation between bands. Coupler A was constructed using three cascaded coupled-line sections with a band ratio fH/fL of up to 7. Coupler B, with a stub-tapped coupled line, was developed for compactness and has advantages of high band ratio and controllable bandwidth. Couplers A and B are most suited for weak coupling applications. Coupler C was developed for achieving strong coupling while maintaining a high band ratio, and it was constructed using a coupled-line section connected by two uncoupled lines at its two ends. Coupler C has advantages of high band ratio, strong forward-wave coupling, compact size, and easy fabrication. Coupler A, operating at 0.84 and 5.17 GHz with f
_H
/f
_L
= 6.15 and a coupling of -10 dB, and Couplers B and C, operating at 0.7 and 2.6 GHz with f
_H
/f
_L
= 3.71 and couplings of -11 and -3 dB, respectively, were fabricated for demonstration. The measured results validate their superior dual-band performance.