All patents covering the PDP-11 architecture are expired by now. The PDP-11 is completely unencumbered from an intellectual property point of view since 1995. But it's quite interesting to look through the patents. They are now easily accessible via Google Patents. The key PDP-11 architecture patents are:

Other PDP-11 and UNIBUS related patents are:

Design patents covered the visual appearance (uspto term: ornamental design) of the PDP-11 systems and peripherals, for example

The trademarks PDP, UNIBUS, MASSBUS, DEC, and DIGITAL ( d|i|g|i|t|a|l ) are all marked as dead and are thus expired, the last one in April 2010.