Robust Beampattern Research Articles

Robust beampattern control for steerable frequency-invariant beamforming in the presence of sensor imperfections

Robust beampattern control for steerable frequency-invariant beamforming in the presence of sensor imperfections

Optimal synthesis of reconfigurable planar arrays for monopulse radar applications: Use of subarrays and distributions with common aperture tail

An approach for the synthesis of sum and difference patterns in monopulse antennas is described. The proposed approach provides a significant reduction in the complexity of the beam-forming network that is fulfilled by reducing the number of array elements and keeping the elements at the edges of the array that share common excitations for both sum and difference modes. An iterative constrained optimisation method is used where the non-convex lower-bound constraints on the beam pattern are cast as an equivalent multi-convex optimisation problem while concurrently minimising a reweighted l1-norm of the magnitudes of the elements in the beam-forming weight vector. Thus, better radiation performance of beam pattern (e.g. narrower beamwidth, lower peak sidelobe level), a much narrower spatial aperture and a smaller number of elements can be achieved compared with the case of uniformly spaced arrays. To compensate for array imperfection in practice, robust beam pattern constraints are derived in the optimisation stage using a worst-case performance optimisation technique. Numerical examples show the effectiveness and advantages of the proposed synthesis approach.

Robust Waveform Design of Ultrasound Arrays for Medical Imaging.

Sound speed is an effective parameter in designing an optimal beamformer. In conventional ultrasound imaging systems, the beamformer is designed assuming a fixed value of speed, whereas the speed in a tissue is not known precisely and also may fluctuate by a great value. The errors in estimating sound speed may lead to a severe degradation in the reconstructed image, as mainlobe width and sidelobe level of the beampattern are sensitive to the speed variations. In this paper, we consider the design of a transmit beamformer, which is robust to the speed variations. The problem is formulated as a convex optimization problem versus the covariance matrix of the excitation waveforms to obtain a beampattern with predefined mainlobe width and a minimum sidelobe level for all possible variations of speed. Then, by eigen-analysis of the obtained covariance matrix, a set of nonidentical single-carrier short-pulses for the excitation waveforms were designed. Various simulations indicate that the proposed method can yield a robust beampattern whose mainlobe width and sidelobe level almost remain constant by 10% speed variations. In contrast, the beampatterns obtained by nonrobust methods suffer extensive changes.

Design of frequency-invariant robust beam patterns by the oversteering of end-fire arrays

The end-fire steering of a data-independent beamformer is well suited to achieving superdirective performance by a linear array whose aperture is shorter than the wavelength. Here, we focus on frequency-invariant beam patterns obtained by filter-and-sum beamformers that are robust against errors and fluctuations. We demonstrate that the oversteering technique applied to a weakly directive beam pattern can considerably increase the directivity, providing a frequency invariance that is better than those of traditional methods. The performance is evaluated with respect to the maximum constrained directivity that a given array can provide at the lower bound of the frequency band.

Robust beamforming and beamspace DOA estimation using measured array manifold of arbitrary geometry acoustic array

The acoustic diffraction of array supporting structure will result in the large difference of the amplitude and phase response of each hydrophone, which leads to the distortion of beampattern. A method for obtaining the array manifold of arbitrary geometry acoustic array is proposed in this paper. We measured the array response vector in many directions with a fixed angular step in anechoic water tank. The array response vectors were smoothed to eliminate the measurement system error. Using these smoothed array response vectors, the robust beampattern of arbitrary geometry array is obtained via beam synthesis method. A 16 element volumetric acoustic array was constructed and tested in an anechoic water tank. Robust low sidelobe beampatterns based on the measured manifold were formed, and then the beamouputs were used to apply to beamspace high resolution DOA estimation methods. The experimental results show that our method can suppress noise and interferences outside the beam coverage regions, and get high resolution DOA estimation results. When the array geometry has some distortion, the weighting vectors of beamforming can still work well to form good beampatterns, and then get accurate DOA estimation results. This verifies the effectiveness of our proposed method.