The diodes are there because that's what HP did. I would also like to know the exact reason they did that too. :) It seems to work, so I'm sure there's a good reason for that layout.
The Coplanar waveguide specs are as follows:
PCB thickness = 1.6mm
Conductor width = 1.5mm
Conductor gap = 0.28mm
So that makes the trace Impedance = 50.1 ohms according to the Saturn PCB Design Toolkit.
Is there a benefit to going to a thinner board for signal integrity etc? I designed around 1.6mm thickness as it's the most common size (so cheapest, easiest, and quickest to get from China).
I'll have a go at straightening those traces too.
Jared Cabot