Re: [SI-LIST] : Coplanar Transmission Line

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Thu Feb 03 2000 - 18:22:22 PST


Gupta, Garg, Bahl and Bhartia in the book "Microstrip Lines and Slotlines",
Artech House, 1996 discuss this subject in Chapter 7, Coplanar Lines:
Coplanar Waveguide and Coplanar Strips.

They cover both CPW and CPS analysis techniques, design techniques and
practical considerations such as loss, manufacturing tolerances and
transitions to coax, microstrip and slotlines.

They seem to support Jian's definitions.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

Ron Miller wrote:

> Jian > > If you will check MDS or ADS you will find HP's definition by their models > to be coplanar waveguide with or without a ground plane. No mention of > coplanar strips. Since they stole their models and terminology from the > origional research in the MTT Journals, I would tend to side with them. > > Ron Miller > > Jian Zheng wrote: > >> Hi, >> >> I noticed that some people in the SI list consider two coupled strips >> (without ground plane) as co-planar waveguide. However, in the microwave >> terminology, two coupled strips without ground plane is called co-planar >> strips (or CPS). Three strips with two gaps are normally called co-planar >> waveguide (CPW). >> >> Compared to normal microstrip structures (strip over a substrate over a >> ground plane), both CPS or CPW may have less dielectirc loss. The reason is >> that about 50% of the field will be in the air and dielectric loss is less >> important. For microstrip, about 60-95% of the field will be in the >> substrate and the dielectric loss is higher. As metallic loss (loss in the >> metal), CPW normally has less loss too because its metallic path is normally >> wider. It is hard to say for CPS because it really depends upon how wide the >> strip is. >> >> Some clear advantage of CPW and CPS over microstrip are: >> >> (1). CPW and CPS have less dispersion than microstrip. In the other word, >> their equivalent circuit parameters (LRCG) are more constant over a wide >> frequency range. >> >> (2). Another advantage is that it is easier to achieve short circuit which >> are common in microwave: On microstrip, you have to build the via holes for >> the short circuit. On CPW and CPS, you can build them on the surfaces. >> >> One important issue of CPW is the balance of the mode(s). Theoretically, >> there is one fundamental mode (cut off frequency at DC) for a two-conductor >> transmission line system. There are multiple fundamental modes for a >> 3-conductor system. For microstrip and CPS, there are two conductors. Only >> 1-fundamental mode exists. As long as the connectors are far away from >> discontinuities (microwave terminology for interconnects of different >> cross-section shape in the transmission line), only one single balanced >> differential mode can exist. For CPW, there are 3 conductors. There are >> multiple fundamental modes: (1) -1 1 -1; (2) -1 0 1; (3) -1 -1 1.... >> Normally, people use the 1st fundamental mode. However, any discontinuities >> such as a bend can induce the other fundamental modes. People normally use >> wire bonds to connect the -1 conductors to suppress the other higher order >> modes. >> >> I am not sure where you can find text books for this topic. Thanks! >> >> Best regards, >> ---------------------------------------------------------------------------- >> ------------ >> Jian-X. Zheng, Ph.D >> Zeland Software, Inc., Tel: 510-797-8109, Fax: 510-797-8241, Web: >> http://www.zeland.com >> ---------------------------------------------------------------------------- >> ------------ >> >> > -----Original Message----- >> > From: owner-si-list@silab.eng.sun.com >> > [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Roy Leventhal >> > Sent: Thursday, February 03, 2000 10:58 AM >> > To: si-list@silab.eng.sun.com >> > Subject: [SI-LIST] : Coplanar Transmission Line >> > >> > >> > >> > >> > Dear SI Experts, >> > >> > Who out there has worked with coplanar (waveguide-like) >> > transmission lines as >> > opposed to stripline/microstripline? >> > >> > What can you tell me about it other than what I can find in >> > Collins or Bahl & >> > Bhartia? >> > >> > >> > Thanks in advance, >> > >> > >> > Roy >> > >> > >> > >> > **** To unsubscribe from si-list: send e-mail to >> > majordomo@silab.eng.sun.com. In the BODY of message put: >> > UNSUBSCRIBE si-list, for more help, put HELP. >> > si-list archives are accessible at http://www.qsl.net/wb6tpu >> > **** >> > >> > >> >> **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, >> for more help, put HELP. >> si-list archives are accessible at http://www.qsl.net/wb6tpu >> **** > > -- > Ronald B. Miller _\\|//_ Signal Integrity Engineer > (408)487-8017 (' 0-0 ') fax(408)487-8017 > ==========0000-(_)0000=========== > Brocade Communications Systems, 1901 Guadalupe Parkway, San Jose, CA 95131 > rmiller@brocade.com, rbmiller@sjm.infi.net > >

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