WhatColorIsIt you mentioned "manual" installation so I wonder if you're referring to the AntennaPod GitHub. I took a quick look and it appears to be purely source code, even for releases. So, if you downloaded a release zip file I am assuming that you'll need to build the app manually, too.
Edit: I have only done one GitHub install and that provided the APK easily. So, it is possible that I am just unfamiliar with where they would be located with the source directory tree...