3 dB, 90°, DC Block Directional Coupler

The circuit equivalence between coupled-line structures and single-line structures is used to represent the four branches of the branchline directional coupler by means of coupled lines. A new type of directional coupler results (**), in which all the four ports show DC isolation between them. It can be utilized, with no design impairments, up to above 20 GHz, since discontinuities are minimized. It is easily realizable since the gaps between coupled lines are not too small. A compact structure results, suitable for the use in active circuits such as power amplifiers, mixers and so on. Infact, the structure needs no external DC-blocks, having them built inside.