Four-port Microstrip Coupler

Geometry of four-port coupler described in [1]

Schwab and Menzel described the design of microwave components, using planar multilayered structures in [1].  One of the structures described in this work was the four-port microstrip coupler that is shown here.

A FEKO model was created for this structure, with the following specifications:

• d1 = 2.22 mm
  
• d2 = 12.51 mm
  
• s = 10.0 mm
  
• w = 4.6 mm
  

A standard RT/Duroid 5880 substrate with the following characteristics were used in the model:

• ε =2.2
• h = 1.58 mm
  

This design features 4 slots that are cut into the ground plane between the top and bottom transmission line.  These slots are depicted as white squares in the geometry description.  FEKO's implementation of the planar Greens function features the ability to model the slots in the ground plane as magnetic triangles, which means that only the slots are meshed and not the ground plane itself, saving significantly on simulation resources.

Four-port coupler S-parameters

Surface current distribution of the coupler at 3.5 GHz