FWIW, the "single loop terminated in a diode" that provides both
magnetic and electric coupling at the same time is not the only way to
make a directional coupler. It can be done with a ferrite toroid to
measure the current and a capacitive voltage divider to measure the
voltage; it can be done with a pair of identical RF transformers, one
to monitor the voltage (connected step-down across the line) and one to
monitor the current (connected step-up in series with the line). In
fact, RFSim99 has a window you can access from the
Tools--Component--Coupler pulldown menu, that will help design a
directional coupler in several different ways. (Beware that the
coupling they tell you for coupled lines is only for coupling sections
1/4 wave [or 3/4 or 5/4 or...] long.) Of the ones shown there, only
the transformer one is broadband.

Cheers,
Tom