I am planning to build an amplifier with the HEMT CGH40010. In its datasheet (http://www.wolfspeed.com/downloads/dl/file/id/317/product/117/cgh40010.pdf), there is a picture of a evaluation kit on page 8, and an even better picture is on page 9. There, one can see several small 'copper islands' near the microstrip lines from the connectors to the FET, and near C1 for example is a tuning stub (that one which is bent towards the left hand side) and at the end of this stub, there are also a few of these strange copper islands.
I wonder what the purpose of these small copper pieces is. I guess it is either some kind of resonator, or it is for tuning. But in the 2nd case, how does it work? is the idea to 'scratch off' some of the copper with a scalpel to tune the stub, or what exactly is it?