A Novel Wideband Quadrature Coupler with Unequal Power Division Ratio, Controllable Bandwidth and Reflection Level

In this letter, a novel wideband quadrature coupler with a wide range of unequal power division ratios ( k 2 ) is proposed. It consists of four transmission line (TL) sections, two types of coupled line (CL) sections and four short‐circuited stubs. The cascading of four TL sections and the intermediate CL section can effectively expand the realisable range of k 2 over a wideband. Using the proposed design methodology, not only a wide range of k 2 can be achieved, but also controllable fractional bandwidth and reflection level of S 11 (FBW S 11 and RL S 11 ) can be independently designed. From variation curves of characteristic impedances, it can be concluded that the realisable range of k 2 is from 3 to 20 dB when the in‐band isolation is deeper than 10 dB. For verification, a prototype with k 2 = 6 dB is fabricated. The measured results matched well with the simulated results, which verifies the effectiveness of the proposed design approach.