Books on the subject of (airborne) radar

[aerolearner]

Speaking of free-of-charge publications, I would suggest this (click on the "Handle / proxy Url" link):
Electronic Warfare and Radar Systems Engineering Handbook

You can find other technical documents about military airborne radars here and here. Just keep the "site:oai.dtic.mil handle" part of the search string and use other keywords (like these or these).

BR,

aerolearner