Wideband branchline coupler using symmetrical four-strip interdigitated coupler

A wideband 180° branchline coupler with an interdigitated coupler is presented, which is composed of symmetrical four quarter-wavelength strips and replaces a long branch of 3λ_g/4 length in conventional ring hybrid couplers. Using the proposed structure, this coupler has a wideband performance of 62% at the centre frequency with compact size. Furthermore, an excellent power dividing balance of ±0.25 dB and a phase difference of ±2° between output ports are realised. The proposed coupler is easy to design and fabricate with a single dielectric substrate in a microstrip structure.