Wideband 180° hybrid coupler with unequal power division ratio and inputs absorptive behaviors

In this letter, a wideband 180° hybrid coupler with unequal power division ratio and inputs absorptive behaviors is proposed, which consists of a slotline-based four-port network (FPN) and two absorptive cells. The slotline-based FPN is implemented by four transmission line sections, a slotline resonator, two microstrip/slotline transitions and a shunted open-circuit stub, which can achieve wideband isolation and unequal power division. Both absorptive cells are composed of a coupled line and a resistor-loaded shorted stub, which can not only enhance the bandwidth of the hybrid coupler, but also achieve inputs absorptive behaviors for both Port 1 and Port 4. Explicit design equations and detailed analysis are given and discussed. Meanwhile, a prototype with unequal power division ratio of 1:2 and absorptive bandwidth of 200% is selected for design, fabrication and measurement. Finally, the excellent agreement between the EM simulated results and the measured results verifies the effectiveness of the design.