There are a couple of other free transmission line calculators available.
1. - TXLINE 2003 from AWR http://www.mwoffice.com
(you'll need to register to enter the download section.)
It does Microstrip, Stripline, Co-planar Waveguide, CPW Ground, Round Coxial, Slotline, Coupled Microstrip and...
A ground ring is also used to meet NEBS EMC Compliance, GR-78-CORE. A requirement for RBOC equipment.
"Since the discharge is applied to the edge of the modules,
one protective measure to consider is a guarding trace around the perimeter that is clear (say 3/8") of components. This trace should...
