Differnce between Duplexer and Diplexer also Circulator and

Dear all
Could you please explain in simple and clearly, the differnce between duplexer and diplexer .
Other one is the difference between circulator and isolator.
Thank you

Duplex and diplex depends on the use. There is not physical difference. If signals go both directions, like transmitting and receiving, it is called a duplexer. (Think of full duplex to remember the difference.) If signals go one direction only and are sorted by frequency into different paths, it is called a diplexer.

Circulators and isolators are almost exactly the same. The only difference is the third port (relative to the main input and output) being available for the user (circulator) or terminated into a resistive load inside the case (isolator).

A circulator is a three port device. An input to Port A will appear at port B but will not appear at port C. Likewise an input to Port B will appear at port C but will not appear at port A and an input to Port C will appear at port A but will not appear at port B. An isolator is identical except one of the ports is terminated in 50 ohms. Isolators are used on the output of Power Amplifers since they isolate the PA from a load with varying VSWR. If the PA is on Port A, the forward wave appears at Port B (the antenna). Any reflected energy from the antenna will appear on Port C (50 ohm resistor), not on Port A, so the PA will never see the reflected energy. So it always sees a good VSWR.