To Measure the Scattering Parameters of Circulator.

________ is a three-port microwave device that can be lossless and matched at all spots.
The total number of ones in the scattering matrix of an ideal circulator is:
A circulator device can also used as an isolator with a few modifications.
What is the primary characteristic of a circulator?
In which resonance region do most waveguide circulators operate?