[SI-LIST] Re: Fw: Re: why do I need mixed mode S parameters?
- From: Istvan Novak <istvan.novak@xxxxxxxxxx>
- To: axel stein <stein_axel@xxxxxxxxx>
- Date: Thu, 23 Dec 2010 10:28:03 -0500
Hi Axel,
You then need to go back to check the basics: pick a single frequency
where you see
amplification in Sdd21 and check all real and imaginary components that
go into the
formula. Make sure that S21 and S43 real and imaginary components are
<=1, and
S41 and S23 real and imaginary components are <<1, finally make sure you
divide
the sum by two.
Regards,
Istvan
On 12/23/10 09:49, axel stein wrote:
> Hi Peter, Istvan,
>
> yes, I made sure, that my port numbering is correct. I used the scheme, that
> is
> at the very bottom of Jeff's email (port 1 and port 3 being the ports of the
> differential pair on one end and port 2 and port 4 being the ports of the
> differential pair at the other end).
> I also made sure, that my unbalanced S-parameters were making sense. At low
> frequencies, S21 and S43 were close to zero dB and S41 and S23 being below
> -20dB.
>
> One strange thing is, that if I separate all the unbalanced S-parameters in
> real
> and imaginary part (linear) and use the formula from Jeff separately for real
> and imaginary, I end up in having the real part (or the imaginary part) of
> Sdd21
> already above 1 (amplified signal), which indicated to me already, that there
> is
> something wrong.
>
> Any idea what could be wrong?
>
> My Agilent PNA-X is saving the S-parameters in dB-angle format (angle should
> be
> in degrees, not radians). I have converted the amplitude to linear by using
> Sxx_lin = 10^(Sxx_dB / 20). The separation in real and imaginary was done by
> multiplying with cos(angle) and sin(angle).
>
> I can't find, where my blunder is, so any feedback would be greatly
> appreciated.
>
> Best regards,
> axel
>
> --- On Wed, 12/22/10, Peter.Pupalaikis@xxxxxxxxxx
> <Peter.Pupalaikis@xxxxxxxxxx>
> wrote:
>
>
>
>> From: Peter.Pupalaikis@xxxxxxxxxx <Peter.Pupalaikis@xxxxxxxxxx>
>> Subject: Re: [SI-LIST] Re: why do I need mixed mode S parameters?
>> To: "axel stein" <stein_axel@xxxxxxxxx>
>> Cc: si-list@xxxxxxxxxxxxx
>> Date: Wednesday, December 22, 2010, 2:01 PM
>>
>>
>> Hi Axel:
>>
>> I get S31-S41-S32+S42.
>>
>> The reason that this is different from Jeff's result is the port numbering
>> (which is why doing this with formulas really stinks).
>>
>> Jeff's result seems to be for ports numbered:
>>
>> 1 2
>> 3 4
>>
>> My formula is for ports numbered
>>
>> 1 3
>> 2 4
>>
>> (where the left two numbers are the +/- singled ended ports that form mixed
>> mode port 1 and the
>> right two numbers are the +/- single ended ports that form mixed mode port
>> 2).
>>
>>
>> You will need to verify your port numbering in order to get the correct
>> results.
>>
>> Pete
>>
>>
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>> |[SI-LIST] Re: why do I need mixed mode S parameters?
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>> I have tried to use the formula from below to convert 4-port S-parameters
>> to a
>> SDD21 value. Unfortunately, the results was not even close to what my VNA
>> would
>> give me when directly displaying SDD21.
>>
>> What I did was:
>> -measured the 4-port S-parameters --> results are available in dB-angle
>> format.
>> -I have converted the values first to linear-angle and then to linear_real
>> -
>> linear-imaginary format.
>> -I have added / subracted the linear_real values according to the formula
>> below.
>> -I have added / subtracted the linear_imaginary values according to the
>> formula
>> below.
>> -I converted the linear_real & linear_imaginary portions of the calculated
>> SDD21
>> back to linear-angle and finally dB-angle format.
>>
>> My expectating would have been, that the SDD21 values that I have
>> calculated
>> this way would be reasonably similar to the directly measured SDD21,
>> however
>> these two are showing significant differences.
>>
>> What have I missed here?
>>
>> Thanks for your kind help,
>> axel
>>
>> ___________________
>>
>> Loyer, Jeff wrote:
>>
>>
>>> The formula that I know of is:
>>> SDD21 = 1/2 (S21 - S41 - S23 + S43)
>>>
>>> For the reciprocal, symmetric system, S21 = S43, and S41 = S23. My
>>> algebra says that, for this system, SDD21 = S21 - S41. I didn't check
>>> your Maxim reference; please double-check it and let me know if it still
>>> disagrees with the formula.
>>>
>>> Also, a quick Google search of "Pozar book" would've found the
>>> information about that book - my thanks to Jeff of Agilent for providing
>>> that info.
>>>
>>> Not to beat you up, but please invest a few ergs before responding
>>> (especially to the entire list) - I invest a bit of time in my responses
>>> (to keep from asking the obvious, mis-stating information, and/or
>>> embarrassing my employer), and I appreciate others doing the same.
>>>
>>> Aside from that, I welcome folks letting me know if I've goofed and/or
>>> asking for clarification.
>>>
>>> Jeff Loyer
>>>
>>>
>>> -----Original Message-----
>>>
>>>> For example, for the following circuit:
>>>> p1 ------- p2
>>>> p3 ------- p4
>>>>
>>>>
>>
>>
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