Microwave PCB design


Simon G8DMN
 

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


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


--
Robin Szemeti - G1YFG


geoffrey pike
 

Is the quadrant not a capacitor?
Geoff
GI0GDP

On Tuesday, 21 September 2021, 15:16:35 BST, Robin Szemeti - G1YFG <robin@...> wrote:


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


--
Robin Szemeti - G1YFG


Simon G8DMN
 

If it is a quarter-wave radius (or anything over the 1/10 or 1/8 wavelength rule of thumb) then it's into transmission line territory and all starts getting rather complicated. There's a lot of confusion about power / ground planes where the size means there's a significant transit time involved.
Simon G8DMN


Robin Szemeti - G1YFG
 

I always thought of them as 1/4 waves .. but, I could be wrong ...


On Tue, 21 Sept 2021 at 18:29, Simon G8DMN via groups.io <simon.rundle=talk21.com@groups.io> wrote:
If it is a quarter-wave radius (or anything over the 1/10 or 1/8 wavelength rule of thumb) then it's into transmission line territory and all starts getting rather complicated. There's a lot of confusion about power / ground planes where the size means there's a significant transit time involved.
Simon G8DMN


--
Robin Szemeti - G1YFG


Tim, VK2XAX
 

Hi all,

Do a search with google for "butterfly radial stub" for all the info and maths you might want :)

cheers

Tim


--
VK2XAX : QF56if : ITU59 : CQ30 : BMARC : WIA


Stefan
 

quarterwave radial stub

https://www.youtube.com/watch?v=IKXpeRDzdDI


----- Original Message -----
From:
UKMicrowaves@groups.io

To:
<UKMicrowaves@groups.io>
Cc:

Sent:
Tue, 21 Sep 2021 21:24:24 +0100
Subject:
Re: [UKMicrowaves] Microwave PCB design


I always thought of them as 1/4 waves .. but, I could be wrong ...


On Tue, 21 Sept 2021 at 18:29, Simon G8DMN via groups.io <simon.rundle=talk21.com@groups.io> wrote:
If it is a quarter-wave radius (or anything over the 1/10 or 1/8 wavelength rule of thumb) then it's into transmission line territory and all starts getting rather complicated. There's a lot of confusion about power / ground planes where the size means there's a significant transit time involved.
Simon G8DMN


--
Robin Szemeti - G1YFG

Email sent using Optus Webmail


Simon G8DMN
 

Thanks, everyone. This was my first post here, so I'm very pleased with the responses.

73, Simon G8DMN