Can't see the fun in that. A rigid axle is a rigid axle, as opposed to the classic tatra swinging half-axle.
Portals are a gear to offset the diff and driveshaft from the center of the hub to get better ground clearance.
Rigid axles comes with, like in the case of the Unimog, or without, like LR Defender, portals.
Independent suspension can also be fitted with portals like the Humvee.
Tatra normally don't use rigid axles - thats why they call it tatra-rigid - because it's exactly what it is...