What is meant by S-G-S and S-G-S-G-S ?

Do you mean G-S-G and G-S-G-S-G?

This desribes the pads where you touch down the wafer prober. G stands for ground and S stands for signal. So G-S-G is a normal coplanar port (one signal with ground on both sides) and G-S-G-S-G are two signals, with one ground pad between them and ground pads on the sides.

I guess Volker already explained very well. Just to add few more sentences and example to make it further.

Signal-Ground-Signal (SGS) is for types of coplanar probes used in especially high frequency chips&wafers to measure characteristics. GSGSG is double channel version.

You can take a look for further & better explanation (than mine )

http://www.mwjournal.com/article.asp?HH_ID=AR_3159

http://goliath.ecnext.com/coms2/gi_0...be-basics.html

Thank you both. So it must be important to make a detailed distinction about the order of ground and signal probes? I am trying to learn about de-embedding.