Thanks for all the reply online and offline. The problem is solved with the suggestions I received. SI list rocks ! Regards Perry ======================================= Perry Qu Design & Qualification, Alcatel Canada 600 March Road, Ottawa ON, K2K 2E6 DID: 613-7846720 Fax: 613-5993642 Email: perry.qu@xxxxxxxxxxx ======================================= -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Perry Qu Sent: Tuesday, September 26, 2006 2:14 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Question for CST Microwave Studio experts Hi, We are evaluating CST MWS recently and I'm having some issues with the waveguide port solutions. Set up a simple differential through via (microstrip on top layer of PCB to microstrip on bottom, no stubs) and try to study the impact of antipad clearance on the differential return loss and insertion loss. Using waveguide port and multipin definition, I got the differential insertion loss and return loss. The insertion loss curve looks rather wield, as I have -0.7dB loss from DC to about 4GHz, but then it climbs up to -0.4 dB from 4 to 10 GHz. I can't explain why I have higher insertion loss at low frequency. Single-ended S parameter computed from the mixed model results show the same trend. Using the exact same model but replace waveguide ports with discrete port and re-run the same simulation. The resulted single-ended insertion loss makes sense where I have a nice slope with very small insertion loss at low frequency and increase linearly as frequency goes higher. I had a few email exchange with CST tech support but I have not received a good explanation. I was wondering if any users here on the list have similar problem ? Thanks Perry ======================================= Perry Qu Design & Qualification, Alcatel Canada 600 March Road, Ottawa ON, K2K 2E6 DID: 613-7846720 Fax: 613-5993642 Email: perry.qu@xxxxxxxxxxx ======================================= ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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 ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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