Re: Microwave PCB design


Robin Szemeti - G1YFG
 

They are a 1/4 wave choke ... the track leading to it will be as thin as possible, to be as inductive as possible, the radius of the arc is 1/4 wave, taking into account the propogation velocity of the substrate. 

A quadrant arc allows them a point contact on the conductor, and the increased width lowers the impedance. Effectively it is like connecting lots of infinitely thin 1/4 wave stubs to the same point, then fanning them out.

I *think* they are normally placed around 3/4 of a wave up the thin track, to put them at a high impedance point and increase their effect.  Thats what I normally do with them anyway.



On Tue, 21 Sept 2021 at 14:44, Simon G8DMN via groups.io <simon.rundle=talk21.com@groups.io> wrote:
Hi,
Looking at various microwave PCB layouts, I see small quadrant shapes half-way along thin tracks feeding DC to amplifier stages. I presume they are capacitors forming a low-pass filter with the inductance of the thin tracks. However, despite searching online, I can find nothing about these gadgets, e.g. why quadrant shaped, how big etc. Can anyone point me at some information? Thanks for any help.
73
Simon G8DMN


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Robin Szemeti - G1YFG

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