[SI-LIST] Re: ADS Momentum simulation of a differential transmission line

Hello Chen,

It reflects that you are using thick substrate for these frequencies. 30GHz and 
beyond falls in millimeter wave region and the insertion loss may be impacted 
due to surface wave propagation or due to waveguide mode propagation.

You need to lower dielectric thickness to push out the dip towards higher 
frequencies. 

I do not have experience with FR4 substrate at these frequencies as for 
majority of MMWave applications I either used RT Duriod or Alumina. 
 
Sanjeev Gupta
Agilent Technologies

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Chen Jikai
Sent: Monday, July 27, 2009 12:48 PM
To: Aubrey Sparkman; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ADS Momentum simulation of a differential transmission 
line

Sorry by S21 I actually mean SDD21 as we defined the ports differentially.



________________________________
From: Aubrey Sparkman <asparkman@xxxxxxxxxxxxx>
To: Chen Jikai <yfgchen@xxxxxxxxxxxx>; si-list@xxxxxxxxxxxxx
Sent: Monday, July 27, 2009 3:19:56 PM
Subject: RE: [SI-LIST] ADS Momentum simulation of a differential transmission 
line

Chen,

If you are speaking about S21 instead of SDD21, that is expected behavior
due to the resonance between the two traces.  Does S41 have a peak at about
the same frequency?  Add a solder mask layer and you can bring down and
control the frequency of the dip point.

Try converting to Sdd21 and look at that for your expected behavior.


Aubrey Sparkman
Aubrey.K.Sparkman@xxxxxxxx

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Chen Jikai
Sent: Monday, July 27, 2009 1:44 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] ADS Momentum simulation of a differential transmission
line

Hi all,
We have been simulating a differential microstrip using ADS Momentum. One
weird thing we observed is that the loss is not monotonic. S21 rolls off as
expected from DC to around 30G. However, from 30G, it increases until about
60G. Since it's just a simple transmission line, involving no
discontinuities, shouldn't S21 be monotonic? Does anyone know what could be
causing this problem?

Thanks a million in advance.



      

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