FreeLists / si-list / [SI-LIST] Re: Balun measurement

[steve weir <weirsi@xxxxxxxxxx>]

Ron generally that is true.  However, PSPL has an interesting Tx line 
balun: 5310-104 that has very tight gain matching and phase linearity 
over the 100MHz to 4GHz range.

Best Regards,


Steve.
ronald miller wrote:
> dont use baluns for measurements.... using network analyzers.
> They are only useful for narrowband applications...
>
> ron
>
> john wrote:
>
>   
>> All,
>>
>>
>> I measured a 1:1 balun as a three port network, port 1 is the unbalanced 
>> input, port 2 is the 'through' connection and port 3 is the indirect
>> connection. I only have a two port VNA so the unused ports were 
>> terminated with 50 Ohms during the measurements
>>
>>
>> Port 1 -----OOOOOOOOO--------o Port 2
>>            o-OOOOOOOOO--o
>>            |            |
>>            |            |
>>           ---           |
>>           GND           |
>>                         |
>>                         ----o Port 3
>>
>>
>>
>> With this 1:1 Balun the Balanced port has differential impedance of 50 
>> Ohms so terminating with the VNA/terminator into 50 Ohms on say ports 2 
>> and 3 gives a large impedance mismatch. The the application circuits for 
>> the chip to which the balanced input connects shows a 100 Ohm resistance 
>> directly across the pins of the balance port (2-3) which is then tracked 
>> at 100 Ohms differential to the device where it is internally terminated 
>> with 100 Ohms. Now using the same test board, I solder a resistor 
>> (infarct three 300 Ohms in parallel) across ports 2 and 3 and re-measure 
>> I have should have the correctly terminated case.
>>
>> I took the balun off the test board and measured the terminator across 
>> ports 2 and 3.
>>
>> I then simulated the terminated case using the s-parameters from the 
>> first measurement and those from the resistor only measurement and 
>> compare them to the terminated case measurement.
>>
>> In general there is reasonable correlation in shape between S11, S22 and 
>> S33. However the simulated S11 has less loss than the measurement of the 
>> terminated case. the simulated S22 and S23 again have the same overall 
>> shape as the measured results although the anti-resonances are not as great.
>>
>> The through S21/S12 S13/31 however show little correlation between the 
>> simulated and measured results having large anti resonances where the 
>> measured results do not.
>>
>> As this is part of an overall simulation I would like to get the Balun 
>> measured and simulating correctly before addressing the rest of the 
>> simulation.
>>
>>
>> Can anyone suggest a better way of measuring the balun ?
>>
>>
>> Regards
>>
>>
>> John
>>
>>
>>
>>
>>
>>
>>
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>>
>>
>>  
>>
>>     
>
>   


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