Hi Jon,

It's an RF device that has at least three ports (but can have more). The
ports are numbered. RF energy entering at one port can only go "around" the
sequence of ports in one direction. So, for example, if the "circulation
direction" is from 1 to 2 to 3, then RF entering at port one can travel to
port 2 but not directly to port 3, it will only go to port 3 if it is not
completely absorbed at port 2 (i.e., if there isn't a correct match at port
2). RF energy entering at port 2 goes directly to port 3 but not directly
to port 1, etc. A more concise way of saying this might be "RF entering at
a particular port is directed completely to the next port in the
circulation direction, provided that next port is correctly terminated."

In practice, they work imperfectly and there is some insertion loss and
also some RF energy does go around the wrong way (even with properly
terminated ports), but it is usually attenuated by about 20dB (called the
isolation).

They are used in some situations to allow a transmitter and receiver to be
connected to the same antenna. In the above example, if you attach the
transmitter to port 1, the antenna to port 2 and the receiver to port 3,
theoretically all of the TX power would go to the antenna and all the RX
power would go to the RX.

They are usually made using ferrite materials which cause Faraday rotation
(that is, a rotation of the polarization of the wave which is different as
it goes through one direction versus the other direction). This
non-reciprocal behavior is used (along with polarizers, I think) to allow
propagation in one direction but not the other.

In my particular instance, although I have way too many irons in the fire
already, I am gathering parts that I need for my amateur weather radar
project (which I mentioned on the list a few months ago). The circulator
would be the main T/R "switch" for the system, allowing the TX and RX to be
connected to the same antenna. I already have a 20 Watt 3.45 GHz amplifier,
some microwave cables, and a 3 foot parabolic dish. I also just completed
the design of the local oscillator unit for the system (a dual PLL,
producing 640MHz and 2.8GHz signals) and I've got all the parts. I plan to
assemble and test it over my Christmas break coming up.

Sean


At 01:59 AM 12/16/01 +0000, you wrote:
>Forgive my naivety. but what is a circulator exactly? Its not a term I've
>come accross before.
>
>Jon
>
>--
>http://www.piclist.com hint: The PICList is archived three different
>ways.  See http://www.piclist.com/#archives for details.

----------------------------------------------------
Sign Up for NetZero Platinum Today
Only $9.95 per month!
http://my.netzero.net/s/signup?r=platinum&refcd=PT97

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.