Q:

Is it more correct to say uncouple or decouple? 

Which is the correct antonym of the verb "couple"? 

A:

AFAIK in Engineering ...

uncouple is used on physical couplings.  Like a train coupling (https://en.wikipedia.org/wiki/Railway_coupling).  To physically detach. 
decouple is used on conceptual and interaction couplings, to allow mutual independence in existence and operation.  For example

decouple the power supply fluctuation from interacting with the amplifier output. 
decouple the correlative interaction between number of active users and the negative feedback about the content of web pages, by providing sufficient resources to serve web pages. 
athletes seek to decouple their motivation to continue a race, from the tiredness of their body and limbs. 

uncouple (ʌnˈkʌpəl)

vb

to disconnect or unfasten or become disconnected or unfastened
(tr) to set loose; release

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

de·cou·ple  (dē-kŭp′əl)

tr.v.  de·cou·pled, de·cou·pling, de·cou·ples

Electronics To reduce or eliminate the coupling of (one circuit or part to another). 
Physics To decrease or eliminate airborne shock waves from (an explosion) by having it take place underground. 
To separate or detach: "Bipeds have a potential advantage over quadrupeds in decoupling their breathing from their locomotion" (Craig Stanford). 

de·cou′pler n.
American Heritage® Dictionary of the English Language, Fifth Edition.  Copyright © 2011 by Houghton Mifflin Harcourt Publishing Company.  Published by Houghton Mifflin Harcourt Publishing Company.  All rights reserved.