Hello,

I am a new engineer to this forum and wanted to ask a question because it seems like you guys are very helpful/knowledgeable here =].

So I have a component in an RF system that looks like a Circulator, but from my understanding, acts like a Pin Diode Modulator.

The input (at Port 1) coming in via rigid (or semi rigid) coax tube is a CW RF signal and gets "modulated" by a digital (voltage) pulse at Port 3 via RG316 cable. The output at Port 2 is a pulsed RF signal.

There is no external power being supplied to this component in question (aside from Port 3's digital pulse), which originally led me to believe it is a circulator, but I did not know a circulator had properties where the input signal could influenced by the 3rd port.

Can you guys please help me identify this component in question?

*added note* The schematic calls this component a "LIMITER/ATTENUATOR"


Thanks in advance!

A big feature of PIN diodes is their large capacitance variation with respect to the bias voltage.  You can use this variation to pass/attenuate signals or tune a channel.  
 

Thank you very much for your response.
I believe it to be a PIN diode at this point.
This PIN diode does not have an external voltage source, which is why I originally believed it to be a circulator. The only voltage source it has is the the pulse voltage input (@ Port 3), which apparently pulses the RF to pass at those moments and causing the pulsed RF signals. My question then is, can circulators function as these PIN diodes the same way? Or alternatively, why does this PIN diode (without an external voltage source) act like a circulator?

Thanks again for the response!

you need to Google circulators and mixers/modulators (which often use PIN diodes). You'll see they are very different animals.   

Haha, thanks for the reply, Higgler.