Antenna Arrays: A Computational Approach

8 Smart Arrays

A smart antenna adapts its receive and/or transmit pattern characteristics in response to the signals in the environment. At least two different antennas comprise a smart antenna, usually in the form of an antenna array. The amplitude and phase of the received signals are weighted and summed in such a way as to meet some desired performance expectation. This chapter describes several different kinds of smart antennas. The first is a retrodirective array that retransmits a received signal back in the same direction. Another type of smart array finds the angular location of signals in the environment, so they are called direction finding (DF) arrays. The simple Adcock array was presented in Chapter 2. In this chapter, arrays that can automatically detect many signals are presented. Antennas that automatically reject interference while still receiving the desired signal are important in an environment with many signals. It may place a null in the direction of an interference source or steer the main beam in the direction of a desired signal. The sidelobe canceller was the first approach to placing a null in the sidelobe of the array pattern. This concept was generalized to the adaptive array that requires signal measurements at each element. A digital beamformer is ideal for this approach due to the complete control of the signals at the elements. It is also possible to adaptively place nulls using a conventional corporate-fed array by using an optimization algorithm ...