A question about CPW feed

There are two ways of CPW feed, one is CPW with ground, the other without ground. what is the difference between these two methods? And how to select between them?
Thanks a lot!

Hmm... I'm not sure what you mean by the two methods. I suppose you mean 'ground' to refer to the metal plane below the normal CPW?

The normal CPW is differential mode signal, but with the ground plane and with shorting pins, we're trying to reduce it to a common mode signal. This is usually preferable because ultimately our equipment needs a ground. But this need not always be the case since we can do a conversion to common mode at the input or output port.

in fact, there is always a metalic ground for support under the cpw substrate, which is called as CBCPW.

when the substrate is thick (thickness>gap), the mode of CBCPW is same as that of CPW (even mode).