Indra has recently completed the development and demonstration of the functionalities of a passive high-resolution primary radar system. The project was sponsored by the European Defence Agency (EDA).

This is the first passive system in the world that is capable of offering images with the application of inverse synthetic aperture radar (ISAR) techniques.

The APIS project (Array Passive ISAR Adaptive Processing) had a 24-month duration. The following entities participated in the project: CNIT (IT) (National Telecommunications Engineering Consortium), Vitrociset Spa (IT), University of Alcala (ES) and University of Cyprus (CH), as well as the Hungarian Science Academy (MTA).

The passive radar is characterised by not emitting any form of radiation, i.e., it uses the signals present in the environment. In the case of Indra's system, the radar uses Digital Terrestrial Television signals as the non-cooperative sources of illumination in the environment.