Hi Steve,

"Steve Nosko" wrote in message
...
This appears to be a blend of co-planar and microstrip.

The freebie program TxLine 2003 "knows" about (can compute dimensions from
impedances, etc.) CPWs, CPWs w/ground planes, microstrips, etc. and you can
get some feel for how wide you can make a CPW w/GP gap before it's effectively
a microstrip -- when the signal trace widths became nearly the same. I dug up
some more Hittite app notes, and it does seem as though they're clearly
playing in the CPW w/GP arena. They do point out that a major downside is
that you eat up a fair number of routing channels with all those vias.

I was part of a program to design a family of his same type of switch on
GaAs, back in the early 90's and the co-planar line was used.

I'm surprised just how much "chaos" there seems to be in the RF IC (primarily
MMIC) arena... there are plenty of old standbys like Hittite, MA/COM (now
Tyco), and Watkins-Johnson, but they seem to have a pretty well stocked
"stable" of components and only introduce a handful of new ones every year.
On the other hand, the little guys and mergers like Freecell, California
Eastern, and RF Micro Devices seems to have lots of good parts that suddenly
get discontinued, product introductions that turn out to be vaporware (a
friend claims that RFMD is great for this -- their data sheets are really part
of their marketing department, with specs drawn strictly from simulation --
they initially quote everyone a lead time of, say, 3 months, and if they don't
get orders for large quantities, they just never fab the chip in the first
place), and otherwise seem a little difficult to rely on at times!

---Joel