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line impedance transformer

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senmeis

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Hi,

as far as I know a line impedance transformer is only valid for a frequency, but the attached one has a bandwidth from 2.5 to 10 GHz. Do I make a mistake?

Senmeis
 

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as far as I know a line impedance transformer is only valid for a frequency, but the attached one has a bandwidth from 2.5 to 10 GHz. Do I make a mistake?
Yes, that is an incorrect assumption.
The line impedance value is valid over the frequency range for which the transformer is designed (has a flat frequency response).

Actually a transformer doesn't have an intrinsic line impedance, it's just the impedance that the input and output are designed for (such as 50Ω or 300Ω).
The transformer open-circuit impedance at its operating frequency is normally much higher.
 

What about λ/4 transmission lines? Does it mean the line length equals to λ/4 and relates only to a single frequency?

Senmeis
 

But if the line length = λ1/4, it cannot equal to λ2/4. That’s why I think a transmission line corresponds only to a frequency.

Senmeis
 

A Ruthroff transmission line transformer doesn't utilize λ/4 or λ/2 stubs. The usual implementation uses a magnetic core to raise the common mode impedance which potentially shorts the signal to a sufficient high level.

In a coreless design, you need to analyze the impedances and electrical lengths of the coupled lines. There may be doubts if it's still a Ruthroff 1:4 unun.
 

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