Testing
the hybrid branch line coupler to see how the PC shop did. FR4 can be
unpredictable as a microwave substrate, but this one measures up pretty well
against the original prototype. In fact, I was concerned about the
repeatability, so I placed compensation pads into the layout. These pads (note
the jumpers) on the small vertical traces allow some adjustment for balancing
the port-to-port coupling.
These couplers balanced out with one pad on each side jumpered over to the trace.
The chart below shows the measurement results.