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

[ronald miller <ron@xxxxxxxxxxx>]

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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-- 
Ronald Miller
Ghz Data, Signal Integrity Consulting
7721 Sunset Ave.
Newark CA  94560
tel     510-793-4744
cell    510-377-9380
fax     510-742-6686
www.ghzdata.com



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