Open quarter wave transformer question

Hello,

I'm using a microstrip quarter wave transformer with an open end connected to a short stub(part of impedance matching for a transistor).

As far as I know a wider microstrip(smaller Z0) for the transformer would result in better bandwidth. However I cannot understand why!

Can you help me with understanding the connection between the bandwidth and the impedance of the line?

I'm currently using "Microwave transistor amplifiers: analysis and design" by Gonzalez, and I don't have access to ieee or similar sites.

Any suggestions would be helpful. :D

Edit:
From: http://www.microwaves101.com/encyclo...ave.cfm#radial
This is what I'm trying to understand (not that i don't trust microwaves101 :P )

Thanks!

Hello,

When the Zo is lower then the tolerances of the line length becomes less critical. It happens because due to the formula Zo*j*tan(BL). So for large Zo the value of the expression will vary more with respect to the line length

cheers.
akr