Miniaturized 7λ/6 rat race coupler with microstrip-to-CPW broadside-coupled structure and stepped-impedance sections

Miniaturization of the rat race coupler is implemented by incorporating a microstrip-to-coplanar waveguide (CPW) broadside-coupled structure and stepped-impedance line sections into the design. The former is used to replace the 4lambda/6-section and the latter is to substitute the lambda/6-sections in a 7lambda/6-rat race. The circuit occupies only 8.9% of the area of a traditional rat race of 3lambda/2 circumference. It is believed that it has the best size reduction in comparison with those in open literature. Measurement results are shown to validate the design and theoretical prediction.