Introduction au STAP: 1. Contexte Radar et Enjeu du Filtrage

Introduction au STAP: 1. Contexte Radar et Enjeu du Filtrage

Marc Montécot François Le Chevalier  Laurent Savy 

Thales Systèmes Aéroportés, 2 Avenue Gay Lussac, F-78851 Elancourt Cedex

THALES Air Operations, 3 Avenue Charles Lindbergh, F-94628 Rungis

ONERA, the French Aerospace Lab, BP 80100, F-91123 Palaiseau Cedex

Page: 
15-34
|
DOI: 
https://doi.org/10.3166/TS.28.15-34
Received: 
N/A
| |
Accepted: 
N/A
| | Citation

OPEN ACCESS

Abstract: 

Space-Time Adaptive Processing (STAP) is a technique useful when the distribution of disturbances exhibits a strong coupling between space (or angular) and time (or range, or Doppler) dimensions. A typical example of such situations is observed with airborne radars where clutter echoes from a specific direction come with a specific Doppler shift. The filtering of these clutter echoes will be more efficient if this relation is taken into account. The main examples of such situations for airborne radars are the detection of ground targets – where the targets are partly masked by clutter echoes coming through the main lobe of the antenna – , and the detection of air targets, where the target returns are competing with clutter echoes coming from other directions, through the sidelobes of the antenna. Space-time adaptive processing is also helpful in many other situations, e.g. communication systems, satellite navigations systems, or active sonar detection systems, where similar couplings exist between the space and time dimensions for disturbances (jamming, or reverberation in sonar).

RÉSUMÉ

Les traitements adaptatifs spatio-temporels, en anglais Space Time Adaptive Processing (STAP), sont des traitements qui exploitent conjointement les deux dimensions spatiale et temporelle des signaux reçus sur un réseau d’antennes, contrairement au traitement d’antenne classique qui n’exploite que la dimension spatiale, pour leur filtrage/séparation. L’arrivée des antennes actives à réception multivoies ainsi que l’accroissement des capacités de calcul des machines de traitements embarquées ont permis l’implémentation de ces techniques. L’objectif de cet article est de montrer dans un contexte radar aéroporté, l’apport de ces traitements en fonctions des différentes missions (ou fonctions radar) que ce soit en mission Air / Sol (détection des cibles terrestres mobiles) ou en mission Air / Air (détections des cibles aériennes). Deux configurations canoniques mettant en évidence l’intérêt des traitements STAP seront étudiées : la configuration radar à antenne à implantation latérale (application Air/Sol pour la détection des cibles lentes sur avion de surveillance) et la configuration radar à antenne à implantation frontale (application Air/Air et détection des cibles aériennes sur avion de combat). Des exemples concrets pour ces deux types de missions seront présentés. Cependant, en introduction, nous rappellerons quelques applications autres que celles du radar aéroporté où ces traitements spatio-temporel peuvent être appliqués.

Extended Abstract

In this paper, the airborne radar situation is described in detail, with examples of clutter localisation in space-time domain, and some results obtained with a real radar.

Airborne pulse-Doppler radars transmit bursts of periodic pulses, which provide a correct detection capability, but remain ambiguous in range and Doppler. The typical output of such a radar is a range Doppler map, as shown in Figure 1 for a medium repetition frequency mode (forward-looking radar), where clutter is distributed according to the geometrical configuration (platform movement, beam pointing, etc.). The detection performance is severely reduced for some Doppler areas, and STAP is a way to mitigate these limitations.

The other typical situation where STAP brings valuable benefits is the sidelooking configuration, where there is a direct relation between the azimuth and the Doppler effect of clutter echoes. In such situations, the minimum detectable velocity is largely improved with STAP due to the high resolution and adaptivity properties of such filtering (Figure 8).

In this example, STAP can simply be analysed either as an angular processing after Doppler analysis (post-Doppler architecture), or as a movement compensation implemented on time signals (pre-Doppler architecture).

For forward-looking radars, the situation, though more complex to visualize, is similar, but the clutter echoes are distributed along an ellipse in the angle-Dopppler plane. In this situation, STAP again brings substantial benefits, by drastically reducing the range-Doppler areas where detection is limited by clutter. This has been demonstrated in realistic simulations (Figure 16) and validated through real measurements (Figure 17).

This brief overview of STAP application for airborne radars illustrates how nonisotropic distribution of disturbances can be taken into account, and the expected benefits for typical situations, through high resolution in angle and velocity and adaptivity to real situations.

Keywords: 

radar, STAP, GMTI, air to air, post or pre doppler.

MOTS-CLÉS

radar, STAP, GMTI, air/ air missions, post ou pré doppler

1. Introduction
2. STAP et Traitement des Signaux Radar
3. Conclusion
  References

Bidon S. (2011). Introduction au STAP. Partie II : Modèle des signaux et principe du filtrage. Revue Traitement du signal, 2011.

Brennan L.E., Reed I.S., (1973). Theory of adaptive radar. IEEE Transactions on Aerospace and Electronic Systems, vol. 9, n°. 2, p. 237-252.

Carrie G., Vincent F., Deloues T., Piétin D., Renard A., Letestu F., (2006). Adapting STAP Processors to GNSS Receivers. European Navigation Conference.

Doisy Y., Deruaz L., Van Ijsselmuide S.P., Beerens S.P., Been R., (2008). Reverberation Suppression Using Wideband Doppler-Sensitive Pulses. IEEE J. Oceanic Engineering, vol. 33, n°4.

Kelly E.J., (1986). An adaptive detection algorithm. IEEE Transactions on Aerospace and Electronic Systems, vol. 22, n° 1, p. 115-127.

Klemm R., (2002). Principles of Space-time adaptive processing. London, UK, The Institution of Electrical Engineers.

Lacomme Ph., Marchais J.C., Hardange J.P., Normant E., (2001). Air and spaceborne systems: An Introduction. SPIE

Le Chevalier F., (2002). Principles of radar and sonar signal processing. Artech House.

Le Chevalier F., Montécot M., Doisy Y., Letestu F., Chevalier P., (2009 ). STAP developments in Thales. Radar conference Eurad 2009.

Le Chevalier F., Savy L., (2009). Traitements adaptatifs spatiotemporels en radar: une analyse relative des traitements radar STAP Pré-Doppler et Post-Doppler. Techniques de l’Ingénieur.

Melvin W.L., (2004). A STAP overview. IEEE Aerospace and Electronic Systems Magazine, vol 19, Issue 1, Part 2, p 19-35.

Nickel U., (2007). Detection with Adaptive Arrays with Irregular Digital Subarrays. 2007 IEEE Radar Conference, 17-20, p 635-640.

Paulraj A.J., Papadias C., (1997). Space-Time Processing for wireless Communications. Signal Processing Magazine, vol. 14, n°6, p.49-83.

Pipon F., Chevalier P, Vila P., Monot JJ., (1997). Joint spatial and temporal equalization for channels with ISI and CCI – Theoretical and experimental results for a base station reception. Proc. IEEE SP Workshop on Signal Processing advances in Wireless Communications, SPAWC, Paris (France), p. 309-312.

Richardson P.G., (1999). Space-time adaptive processing for manoeuvring airborne radar. IEE Electronics and Communication Engineering Journal, p. 57-63.

Savy L., (2006). Benefits of Space-Time Adaptive Processing for Air to Air Operations. Proc. CIE Int’l Conf of Radar (IEEE Press), Shanghai, China.

Savy L., Richardson P., Medley J., Buerger W., (2009). The relative merits of pre/post-Doppler STAP, Radar’09 international Conference, October 12th-16th 2009, Bordeaux.

Ward J., (1994). Space-time adaptive processing for airborne radar. Lincoln Laboratory MIT aTechnical report n° 1015.