Dual-/Tri-Band Branch Line Couplers With High Power Division Isolation Using Coupled Lines

Two novel dual-/tri-band branch line couplers with high power division isolation using coupled lines are proposed in this brief. Two conventional couplers loaded with quarter-wavelength open/shorted coupled lines are adopted to realize the dual or triple bands. Each band has a high isolation due to the introduced transmission zeros. The center frequencies of the two planar couplers can be adjusted over a wide frequency band by changing the even/odd-mode characteristic impedances of the coupled lines. Two planar dual-/tri-band couplers located at 0.75/1.32 GHz, 0.69/1.0/1.4 GHz are designed and fabricated for verification. Good agreement can be observed between measured results and theoretical expectations.