WordNet records no synonym and no antonym for electronic reconnaissance. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the detection and identification and evaluation and location of foreign electromagnetic radiations (other than radioactive)
Synonyms, antonyms and the broader and narrower relations for electronic reconnaissance come from Princeton University’s WordNet. Full sources and licences.