A Harmonic and Size Reduced Ring Hybrid Using Coupled Lines

Parallel coupled lines are applied to design a microstrip ring hybrid for size reduction and harmonic suppression. A properly combined parallel coupled line with an open stub shows a low pass filter characteristic and equivalently lambda/4 electrical length. By substituting the coupled line for each one of the six lambda/4 parts in the conventional ring hybrid, we achieve both significant size reduction and excellent harmonic suppression without the degradation of the hybrid characteristic itself. The size of the fabricated ring hybrid is one fourth of the conventional one, and the simulated and the measured second and third harmonics are suppressed about 20dB