ABSTRACT
Adaptive beamforming is used to optimize the signal-to-noise ratio (SNR) in the look-direction (LD) by carefully steering nulls in the beam pattern toward the direction(s) of interference sources. This chapter presents adaptive beamforming using two distinct techniques that parallel the two adaptive filtering techniques these are block least squares and projection-based least-squared error. Fundamental to the traditional approach to adaptive beamforming is the idea of exploiting some of the received signal information to improve the SNR of the array output in the desired LD. The array SNR gain and LD beam-width are still defined based on the wavelength-to-aperture ratio, but an additional interference rejection can be obtained by adaptively “nulling” the array output in the direction of an interfering source. Frequency-modulated continuous wave signals have the advantage of concentrating the transmitted signal in a narrowband to give high SNR and sweeping the signal in frequency precisely to measure propagation times to multiple reflectors in the transmitted beam.
