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How a 90 degree MS or strip line is converted to spiral which shows the same result?

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mfarhan1

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Dear all
I have a basic question, most of you had experience on that.
You often came across a paper of coupler, balun in which after designing, the author claims that he had made the coupled line in form of spiral and do the broadside coupling to save the space now I am utterly confused that how a 90 degree MS or strip line is converted to spiral which shows same result. Spiral has mutual inductance between lines and ground soHow to model a spiral equivalent of microstrip, (simulation do help but there has to be a good starting point).

Second question: Spiral once made will have some inductance in it and that will change the reactive part of input impedance! So i believe an impedence matching network is required now to connect this component to others, am i right? or is there any other method

Any resource which exactly talks about same problem will be highly appreciated
I hope I had made my question clear.
Many thanks

I am adding two picture from paper which did same thing with out mentioning any procedure.
 

spiral mutual inductance

Hi,
really spiral strip-microstrip coupled lines either conventional straight coupled lines have mutual inductance. Both cases are Electric-Magnetic coupling.

"Second question: Spiral once made will have some inductance in it and that will change the reactive part of input impedance! So i believe an impedence matching network is required now to connect this component to others, am i right? or is there any other method "

The fact is we have a distributed inductance and also distributed capacitance, if the distributed inductance is increased L' = k*L and distributed capacitance remains the same, a change in Zo result: Zo' = sqrt(k)*sqrt(L/C) = sqrt(k)*Zo

This balun remembers me a "scaled version to microwave" of HF transmission line transformers except for absence of ferrite core...

BR
 

Re: Microstip as spiral

@byteptr
Thanks for your reply, but can you tell me how can i model a spiral MS or SL,
i am modelling 90, 3dB broadside spiral coupler, Now is there any empirical formula or paper which talks on this issue,
Thanks
 

Re: Microstip as spiral

Hi,
Really microstrip acts as transmission line if the EM fields are confined between strip and ground plane, so in first approximation, no coupling must appear.

However, is well know that some dispersion of fields exist and the idea of mutual coupling takes sense. I think that you can see the spiral microstrip line as printed spiral inductor wich has a close a conductor ground plane, this plane acts as short circuited secondary transformer and his effect is viewed as an primary (the spiral microstrip) inductance reduction because short-circuited currents are induced in the ground plane, they are called "eddy currents" (remember the focault effect that is used in many industrial applications and avoided in RF magnetic cores). In addition to this some distributed capacitance effect appear.
Long time ago I founded some formulas in "Radion Engineering" Terman related to this subject.

I don't know if exist a detailed analysis for your case, but you can try one empirical model by means of measures/simulations and some notes.

You can start estimating the mutual coupling in printed inductor, i recommend you this application note: https://ww1.microchip.com/downloads/en/AppNotes/00710c.pdf
(but this assumes the electrical length is short)

And some literature such as Pozar, Wheeler's approximations etc.

Best regards
 

    mfarhan1

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Microstip as spiral

What is the range of Sipral inductor that you are looking at?
Becoz its trade off on capcitance and inductance for a substrate.
On LTCC we can get good cap but not inductor. opposite with the case of resin substrates.
 

Microstip as spiral

@kspalla
Dear i am not interested in having inductor or capacitor all i wanted to know is how to modify the transmission line in shape of spiral that gives same result.
 

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