The main objective of this project is to develop and implement novel detection and avoidance (DAA) systems for urban air mobility aircraft (UAM aircraft), also known as flying cars or air taxis. Indeed, micro-Doppler (mD) detection based on passive radar techniques represents a good avenue. Thereupon, cooperative and non-cooperative navigations are investigated in order to, safely and efficiently, integrate these next generation (NextGen) aircraft into the current airspace. Additionally, Unmanned Aerial Systems Traffic Management (UTM) is envisioned to manage a high magnitude of air traffic where multiple types of flying vehicles should be able to detect and avoid each other. However the existing DAA systems (ACAS, ADS-B and active radars or transponders) have vulnerability issues that make them not really appropriate for a safe navigation throughout a complex urban (dense and cluttered) environment. Furthermore, this project investigates the most suitable signal of opportunity (SOP) to be used in complex urban environment. Non exhaustively, 4G/5G Long Term Evolution (LTE), Digital Video Broadcasting – Terrestrial (DVB-T), WI-FI, Global Navigation Satellite System (GNSS) are considered SOP, should they not be used for their primary purpose but rather as illuminators of opportunity.