Jeff wrote:

They're different animals,

http://www.microwaves101.com/encyclopedia/diplexers.cfm
http://www.microwaves101.com/encyclopedia/duplexers.cfm


That site is wrong!! What they describe as a 'duplexer' in radar is in
fact a circulator, although it is acting as a duplexer.

The term duplexer is generally used for a device that permits
simultaneously transmission and reception on a single antenna, but a
duplexer can be a diplexer where the transmit and receive bands differ.
That is, a diplexer that splits an antenna into 2 isolated ports at
different frequencies is being used as a duplexer. A circulator that
isolates a transmit and receive port at the same or similar frequencies
is also a duplexer but not a diplexer.

Jeff

The definitions I've found generally seem to say a duplexer isolates two
ports on the same, or very close to the same, frequency and that a diplexer
isolates two ports on different bands.

The definitions I've found also generally seem to say a circulator is a 3
or 4 port device in which a signal to a port is directed to only the next
port in order and says nothing about frequencies. And, as you said, is
often used at microwave to act as a duplexer.

I would guess the definative definitions would be what the IEEE dictionary
says, but I don't currently have access to that.