- Ray-tracing output (white lines) and electron density profile (colour map). It is worth noting that for a fixed frequency by decreasing the elevation angle.
- Ray-tracing output (white lines) and electron density profile (colour map). It is worth noting that: greater distances are reached for a fixed elevation angle by increasing the transmitted frequency.
- Example of 3D electron density profile carried out by means of a network of ionosondes. The profile is updated whenever the network of ionosondes records new values
- Receiving antenna array: 3D receiving element
- Receiving antenna array: 3D close look of the receiving antenna array geometry
- Transmitting antenna array: prototype scaled model (1:4) of the transmitting element
- Transmitting antenna array: 3D representation of the transmitting antenna array
- High-level architecture of the LOTHAR system (TX radar site in pink colour, RX radar site in blue colour)
- Example of the ssurveillance area (blue area) which can be illuminated by the LOTHAR system
- HF OTH sky-wave radar principle: the transmitted HF signal is reflected by the ionospheric layers and illuminates targets over the horizon. As a matter of fact the e.m. waves at the aforementioned frequencies are gradually bended through the ionosphere thus extending the coverage of the radar well beyond the line of sight (LoS).
The project is devoted to the feasibility study of a pseudo-monostatic Over The Horizon (OTH) HF sky-wave radar for the surveillance of the Mediterranean area.
The physical principle of a HF OTH sky-wave radar is the ionospheric reflection. Specifically, the transmitted signal is progressively bended during the propagation through the ionospheric layers until it reflects back to the Earth’s surface.
A number of characteristics differentiates these systems respect to conventional microwave radars, for instance:
- The propagation channel is space-time variant;
- The radar performances are strongly dependent on atmospheric, cosmic and man-made noise;
- The HF spectrum is heavily crowded by communication and broadcasting radio.
The main purposes of the project are:
- The characterization and analysis of the critical issues related to system design;
- The definition of technical and functional requirements of the radar;
- The design of the system architecture and the implementation of the radar signal processing chain.
LOTHAR is a distributed system, characterized by following main elements:
- 2D circular phased array. The transmitting array is made up of 50 individual radiating elements and it allows the digital beam-forming at different frequencies. The receiving array is composed by 300 radiating elements;
- The MCU (Main Control Unit) responsible of the management of all radar subsystems. The MCU includes the radar console, the FMS (Frequency Management System) and the ionosphere sounding unit. The MCU provides the 3D electron density profiles and the frequency/elevation angle pairs to be used for covering the surveillance area. The radar console displays detection and tracking data as well as ionospheric data and external noise spectrum;
- The Tx_LCU (Transmitting Local Control Unit) is in charge of generating the signals relative to each transmitting unit as well as the Tx array beamforming;
- The Rx_LCPU (Receiving Local Control Processing) which manages all receiving units to collect and pre-process the received signals.
A network of ionosondes, as well as a sensing system for external noise characterization, are used to adapt the radar functionality to the environment.
The LOTHAR system presents the following innovative concepts:
- High level of flexibility and re-configurability thanks to the SDR implementation;
- 2D antenna array composed of novel wide band radiating elements;
- Independent waveform generation for each transmitting element;
- Innovative techniques for digital array pattern synthesis and radar signal processing;
Multifunction radar (tracking, early-warning and remote sensing);
Introduzione ai sistemi HF-OTH SKYWAVE (Journal Article)
Rivista Marittima, (6), pp. 88-102, 2014, (LOTHAR-FATT).
PROGRESS IN ELECTROMAGNETICS RESEARCH B, 50 , pp. 97–111, 2013, ISSN: 1937-6472, (LOTHAR-FATT).
MSA System Concept for Mediterranean Sea Surveillance (Journal Article)
Information & Security: An International Journal, (2), 2011, (LOTHAR-FATT).
Proceedings of the 2010 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2010, (LOTHAR-FATT).
Cognitive Adaptive Waveform Technique for HF Skywave Radar (Inproceeding)
Cognitive Information Processing (CIP), 2010 2nd International Workshop on, pp. 247–252, Isola d'Elba, Italy, 2010, (LOTHAR-FATT).
Proceedings of the 2009 European Radar Conference, 2009, (LOTHAR-FATT).
A Software-Defined Frequency Management System for HF-OTH Skywave Radar (Inproceeding)
Proceedings of the SENSORS & ELECTRONICS TECHNOLOGY PANEL Specialists Meeting SET-136/RSM-11 on Ã¢ÂÂSOFTWARE DEFINED RADARÃ¢Â?, pp. –, Lisbona, 2009, (LOTHAR-FATT).
HF-OTH Skywave Radar for Missile Detection (Inproceeding)
Proceedings of the SENSORS & ELECTRONICS TECHNOLOGY PANEL Specialists Meeting SET-125 on Ã¢ÂÂSensors and Technology for Defence against TerrorismÃ¢Â?, pp. –, Mannheim, 2008, (LOTHAR-FATT).