Method to Determine the Far-Field Beam Pattern of A Long Array From Subarray Beam Pattern Measurements.

Donghwan Jung,Jeasoo Kim

doi:10.3390/s20041236

Abstract

Beam pattern measurement is essential to verifying the performance of an array sonar. However, common problems in beam pattern measurement of arrays include constraints on achieving the far-field condition and reaching plane waves mainly due to limited measurement space as in acoustic water tank. For this purpose, the conventional method of measuring beam patterns in limited spaces, which transform near-field measurement data into far-field results, is used. However, the conventional method is time-consuming because of the dense spatial sampling. Hence, we devised a method to measure the beam pattern of a discrete line array in limited space based on the subarray method. In this method, a discrete line array with a measurement space that does not satisfy the far-field condition is divided into several subarrays, and the beam pattern of the line array can then be determined from the subarray measurements by the spatial convolution that is equivalent to the multiplication of beam pattern. The proposed method was verified through simulation and experimental measurement on a line array with 256 elements of 16 subarrays.

Highlights

Beam-pattern measurement is essential to verify the performance of an array sonar
As near-field scanning is very time-consuming [2,14], we propose a method based on measurement of subarrays to measure the beam pattern of a long line array in a limited space
The method proposed in this study divides the long discrete line array into subarrays with the same size and estimates the long array beam pattern from the subarray beam pattern

Summary

Introduction

Beam-pattern measurement is essential to verify the performance of an array sonar Such measurements for long arrays generally need a huge testing field or a complex setup [1,2]. It is difficult to measure the beam pattern in an acoustic tank, especially for long arrays operating at high frequencies, because the acoustic tank usually does not meet the far-field conditions. To solve this problem, various studies has been conducted on methods of estimating beam patterns through near-field measurements. Kerns [4] studied planar scanning, and Wacker proposed a method of extracting modal coefficients from spherical near-field measurements and a scheme using the fast

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