Reduced-length tandem directional couplers designed in microstrip technique for use in balanced amplifiers

In this paper, a tandem connection of hybrid couplers realized in microstrip technique is presented. The proposed structure is designed as a tandem connection of two coupled-line sections having different electrical lengths and the same value of coupling coefficient. Such approach can be used to reduce overall size of the component, what is more attractive in comparison to the classic tandem hybrid topology. Furthermore, to verify possibility of implementation in conjunction with active devices, the proposed directional coupler is implemented in two balanced amplifiers utilized in PCB and MMIC technologies operating at 1 GHz and 20 GHz, respectively.