Title changed and old thread deleted. OOPS - you're right. I had "microstrip" and "stripline" backwards in my last e-mail. I meant to question your assertion that stripline is more lossy than microstrip. Thanks for the links, Orin. Looking these over and my old data (including postings to this forum), here's what I think: 1) The IEEE paper is for microstrip w/o soldermask. My own data agrees that microstrip w/o soldermask is slightly less lossy than stripline. 2) Regarding the 2nd link (Eric B.'s posting), I'll ask Eric to share his source data for the assertion that microstrip provides less attenuation than stripline (perhaps he's referring to the same paper). 3) I'm including some verbiage from a previous posting of mine below, including empirical data demonstrating that the difference in loss was negligible. In looking at the data again, there does seem to be more loss on the stripline at 20 GHz, but not until then (the difference between microstrip and stripline at frequencies less than 20GHz are in the noise range). Overall, I think the difference in loss between the 2 is not significant enough to use as a criteria in layer selection. Though I would stress again that, in the practical real-world case, you might well be able to use wider traces on microstrip and thus reduce your loss significantly. That has to be balanced against more crosstalk and worse impedance control, etc. Enjoyed the chat - cheers! NOTE: I apologize to those besides Orin, since I know this data below is going to be converted into "plain text" and the table will look like garbage. With a little work, you can turn it back into reasonable data. ______________ Previous posting verbiage ___________________ Eric's comments got me looking at my data again (that lead me to believe the losses of microstrip and stripline are equivalent). That data was based on simulations (XFX -> Hspice), which my past experience has shown to correlate well to measurements. Assuming the trace width and thickness is kept constant (adjusting the dielectric thickness to achieve the proper impedanct), it showed little difference between microstrip and stripline for our current frequencies of interest (say, up to ~5GHz). I also validated this using ADS, but would love to see anyone's conflicting data. I should point out that this is with soldermask, which I'm assuming most designs will be forced to use. Similar experiments with pure microstrip (no soldermask) showed microstrip to be slightly less lossy than stripline. I also went searching for empirical data comparing microstrip vs. stripline (with trace width/thickness kept constant), and could only come up with differential insertion loss data (which my experience shows to be about the same as single-ended) from some previous test boards. Again, this data suggests there isn't a significant difference in insertion loss between microstrip (ms) and stripline (sl). designator ms/sl length SDD21 (dB/inch) SDD21 (dB/inch) SDD21 (dB/inch) SDD21 (dB/inch) SDD21 (dB/inch) (inches) @ 2GHz @ 5GHz @ 10GHz @ 15GHz @ 20GHz tx ms 3.70 -0.31 -0.64 -1.09 ty ms 6.72 -0.33 -0.68 -0.93 -1.41 -1.95 tz ms 14.73 -0.29 -0.65 -1.24 -1.78 -1.94 sx sl 4.70 -0.32 -0.84 -1.39 -2.82 -2.89 sy sl 10.70 -0.31 -0.70 -1.39 -2.40 -2.48 sz sl 20.00 -0.32 -0.69 -1.10 -1.72 -2.18 When I look at this data, here's what I see: (1) at 2GHz, there's no difference (as expected - conductor loss dominates) (2) at 5GHz, "sx" has significantly more loss than the rest - but hard to believe it's solely because it's stripline. (3) at 10GHz, 2 of the striplines exhibit more loss, but the longest stripline ("sz", which is probably the most reliable, due to its long length), shows the same as the microstrips (actually less than the longest microstrip, "tz"). (4) roughly the same trend as (3) continues up to 20GHz (the data from the shortest microstrip, "tx", was too noisy to make sense of). The dimensions (in mils) were: ms: h=3.5, w=5, s=5, t=1.4; microstrip had soldermask on it. sl: h1=h2=6, w=5, s=5, t=1.4 Standard FR4 was used. ______________ End Previous posting verbiage ___________________ Disclaimer: The content of this message is my personal opinion only and although I am an employee of Intel, the statements I make here in no way represent Intel's position on the issue, nor am I authorized to speak on behalf of Intel on this matter. Jeff Loyer ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu