An RF isolator is a seemingly magic device that allows signals to pass in only one direction. Signals applied to the input port are sent to the test port and signals coming into the test port can only go to the output port. This one-way property is usually accomplished with special non-linear ferrite/magnet structures operating at very high frequencies.
For a typical setup the test generator is connected to the input port, the antenna or device to be tested is connected to the test port, and a signal level monitor is connected to the output port. When the test port is terminated with 50 ohms, no energy