10 GHz oscillator and switch

kitepassion said:

I am going deeper in the projects, I developed a board on FR4 material. I know it is not the best solution but this is what I have and I have to use it.
Thus, I am playing a bit with TXLINE from Microwave office.
I put all the parameters needed, tangent loss, dielectric constant and so on. Then I want to build a coplanar waveguide with the ground. Now what I do not understand is why when I specify 50 ohm of impedance does not matter the length of the line I have to build.
I mean, if I change the parameters such as the width of the trace or the gap the impedance change, but why when I change the length only the electrical length change?
I am a bit lost...
Moreover, attaching to my VCO (adapted) pcb an unmatched network what would happen? There is no spec in the VCO for the VSWR.

Thanks!!

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kh4n said:

yep, length does no change the impedance.
check the `frequency pulling` plot of the VCO to see what happens when the output load is not matched, it will give some idea.

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kitepassion said:

Just to give myself a reply

The impedance is defined as Zo = sqrt(L/C), if I match the characteristic impedance for my circuit (50 ohm), this will not depend on the length of the line. But it is true that going 'through' the line the impedance changes but at its end will be always 50 ohm.

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