Narrowband Beamforming Research Articles

Adaptive antenna array under directional and spatial derivative constraints

The author examines the beampattern dependency on the choice of phase centre location, when a narrow band beamformer is subjected to directional and spatial derivative constraints. He then presents a technique based on a power response approach, for deriving a new set of constraints for controlling the beampattern spatial derivates. The new set of constraints ensure that the array beampattern is independent of the choice of the phase centre co-ordinate origin. It is shown that for the first-order case, the constraint is linear, but for the second-order case, the constraint is quadratic. The author then presents a technique for approximating the effect of the quadratic constraint by two linear constraints. Finally, he presents a technique for optimising the beampattern with respect to the choice of the phase centre location, when the quadratic constraint is being approximated with linear constraints. >

On superresolution effects in maximum likelihood adaptive antenna arrays

The superresolution performance of maximum likelihood (Frost) adaptive antennas is analyzed. Assunming that the adaptive weights have had enough time to converge to the optimal (Wiener) solution, the beampattern and spatial resolution of the array are computed. Simple expressions are derived which allow close-approximation computations of converged adaptive beampatterns using only scalar operations. The analysis applies to narrow-band line-array adaptive beamformers. Computer simulations are presented to verify the excellent match between theoretical and measured beampatterns for small angle deviations from the look direction.

The TAP III beamforming system

The Three-Array Processor (TAP III) beamforming system incorporating both wide-band time-domain beamforming and narrow-band frequency-domain beamforming is described. This paper briefly develops the beamforming theory and shows how the fast Fourier transform (FFT) is applied to accomplish frequency-domain beamforming. The frequency-domain beamformer operates in the frequency domain to form beams and power spectrum data over narrow frequency bands of interest. A real-time digital filtering technique is used to extract the narrow bands of interest from the broad-band input signal. The frequency-domain beamformer accomplishes real-time digital filtering and beamforming by using a high-speed array processor to do the complex calculations and data handling required by the algorithm. The time-domain beamformer operates in parallel with the frequency-domain beamformer to form up to 16 broad-band beams in the time domain. A programmable all-pass digital filter is used to create the fine time delays required by the time-domain beamformer.