Partial disk 36GHz passive component 1

[logbook]

I have just seen an interesting planar structure on a microwave mixer (Agilent AMMC-3040) which operates up to 36GHz. The structure looks like metalisation in the shape of a sector of one sixth of a circular disk (ie 60 degrees worth of a circular disk, 180 degrees being half a circular disk), with the input going to the centre of the circular disk. At a lower frequency this would be a lumped capacitor, but it looks like a distributed line of some type with the capacitance increasing and the inductance decreasing with distance from the feed point.

Can anybody suggest a link to what this structure is or does?

 

[biff44]

Most likely is a quarter wave radial stub, and there is a diode between it and the input line (but it is too small to see). Radial stub gives a fairly broadband short circuit.

 

[logbook]

Biff,
"radial stub" is the key technical phrase here. Just giving it a name has unleashed the power of Google onto the problem. I found the exact structure on the Integrated Engineering Software web page.

http://www.integratedsoft.com/products/singula/examplesradialstub.asp

Your help is greatly appreciated