I needed to find out what this little device does:
So I started typing into the Chrome address bar, "mini circuits" and this is what I saw:
(Click on the image to see clearly what happened.) It somehow KNEW I was going to type 15542 next! I haven't EVER looked up ANYTHING for "Mini Circuits". The last time I looked up something like this was in a paper catalog in the 1990's.
(Answer: It takes the RF signals in 1 and 2 and sums them to the S port, or it takes an RF signal in the S port and splits it evenly into the 1 and the 2 ports. The latter is how it is used in the circuit I am looking at.)