| Smart antennas involve processing of signals induced on an array of sensors such as antennas, microphones, and hydrophones. They have applications in the areas of radar, sonar, medical imaging, and communications.
Smart antennas have the property of spatial filtering, which makes it possible to receive energy from a particular direction while simultaneously blocking it from another direction. This property makes smart antennas a very effective tool in detecting and locating an underwater source of sound such as a submarine without using active sonar. The capacity of smart antennas to direct transmitting energy toward a desired direction makes them useful for medical diagnostic purposes. This characteristic also makes them very useful in canceling an unwanted jamming signal. In a communications system, an unwanted jamming signal is produced by a transmitter in a direction other than the direction of the desired signal. For a medical doctor trying to listen to the sound of a pregnant mother’s heart, the jamming signal is the sound of the baby’s heart.
Processing signals from different sensors involves amplifying each signal before combining them. The amount of gain of each amplifier dictates the properties of the antenna array. To obtain the best possible cancellation of unwanted interferences, the gains of these amplifiers must be adjusted. How to go about doing this depends on many conditions including signal type and overall objectives. For optimal processing, the typical objective is maximizing the output signal-to-noise ratio (SNR). For an array with a specified response in the direction of the desired signal, this is achieved by minimizing the mean output power of the processor subject to specified constraints. In the absence of errors, the beam pattern of the optimized array has the desired response in the signal direction and reduced response in the directions of unwanted interference. |