Detection and estimation in antenna processing: theory

Sensor array antennas play a vital role in many technical fields (sonar, radar, seismic, radio astronomy, echography, transmission and even optics), where they are a highly advantageous replacement for "conventional" antennas, i.e. antennas whose performance is determined by geometry, in particular parabolic reflector antennas.

Among the obstacles encountered in improving "conventional" antennas and resolved by sensor array antennas, we can cite:

• The dilemma between antenna gain (sensitivity) and coverage (ideally panoramic): by using an array antenna with a large number of sensors, you benefit from antenna gain on reception, without compromising panoramic coverage by using electronic pointing.

• The problem of interference in an increasingly congested world: antenna arrays can use much more sophisticated processing than is possible to wire into the geometry, such as supervised cancellation of the interference signal or adaptive apodization.

• The problem of geometric constraints: large antennas (conventional or array) inevitably have to contend with the limited size of the support platform. Array antennas can be adapted to any geometry. They can be deployed in the field (RIAS radar or seismic prospecting). They can even be fitted with variable geometries (towed streamers for seismic prospecting or TBF sonar).

All these problems are solved by using antenna arrays, but they also have other useful properties. The most interesting of these is the ability to share an antenna between several independent users. For example, a base station could serve several subscribers simultaneously in the same channel (SDMA: Spatial Division Multiple Access); a satellite antenna could be pointed at several satellites simultaneously; a radar could provide panoramic coverage without mechanical movement, using several reception channels in parallel (strategic watch). Multisensor recording can be used a posteriori for more efficient antenna processing (seismic, surveillance). Sharing is also a possibility for amortizing the operating costs of an installation.

Furthermore, sensor array antennas are to conventional antennas what sampling is to analog signals (in fact, array antennas are referred to as "spatial" sampling). As such, these antennas are part of the digital revolution.

The intelligence of antenna arrays lies not in their geometry, as might be the case with a parabolic antenna, but in their processing. Talking about antenna processing is therefore unavoidable. We have chosen to present antenna array processing [ ] by first introducing [ ] the useful tools of the statistical...