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[SOLVED] Transmission line based inductor(Choke)

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Full Member level 3
Aug 11, 2010
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HI all,

I am working on Transmission line based circuit at 38Ghz. I have to replace lumped RFc by TL. In MWO office simulation I am getting similar results when using my designed 1 turn meander inductor, 2 turn meander inductor and thin TL.

I know in for a choke , its value should be high, that is for 38GHz, it should be around 6 nH (around 1431 Ohms). Now when I measure the inductance of my designed inductor I ma getting 1.8nH, 1.8nH and 1.2 nH respectively. The highest XL is around 429 Ohm. It is still 5 times larger than 50 Ohms. Is it oky to use these designed inductor then?

As per simulation the results are same, but really do not know what to do?

Any help would be greatly appreciated.


I don't know much about the dynamics of transmission lines.

Regarding inductors...

To achieve a specific time constant, you must pair up a small choke with high current...
and you must pair up a large choke with small current.

If you examine behavior of all LR combinations which match a given TC...
They will also show matching internal EMF values throughout a cycle.
They will also show matching flux field intensities at all points in the cycle.

The only difference will be in amp flow.
Currents will be smaller with a large choke. And larger with a small choke.

Don't know if this helps.

If the device you need is a choke (passing DC but rejecting RF), then its RF impedance should be as high as possible. If it is ten times the 50 Ohms, it looks good. This means it will reflect the RF signal back and pass DC and low frequency if there is some.


When it is a narrow band application, can you make it electrically 0.25 lambda long (and short the DC supply side)?

Regarding the impedance, this depends on the impedance level at the connection. When it is 50 Ohms (low VSWR in that line), 5 .. 10 times will be fine, but when that 50 Ohms line is part of a resonator (so High VSWR), it may not be fine (depending on the position on that 50 Ohms line).


When I designed 38G system, I had used 1/4lamda+radio stub(45 deg fan stub), and it is good. It is very small at 38G, but it works. I remembered the simulated result of the foresaid is about -20dB attenuation for 38G.

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