截断阶梯Legendre函数加权阵列恒定束宽波束特性分析*

连续Legendre函数加权的恒定束宽换能器(CBT)阵列可以在一定频率范围内采用与频率无关的简单阵元权重实现恒定束宽的波束特性。然而常规CBT阵列需要为每个阵元配置相应的阵元权重,当阵元数量较大时会增加复杂度。该文分析了截断阶梯Legendre函数加权的面阵列,包括球面阵、柱面阵和平面阵,并且分别分析了Legendre函数球面加权方法和Legendre函数柱面加权方法应用于上述阵列的性能。结果表明,截断阶梯Legendre函数加权对波束方向的影响可以忽略,而主要影响波束宽度。对于面阵列,当采样阶梯不大于3 dB,截断点不大于-21 dB时,截断阶梯Legendre函数加权能很好近似连续Legendre函数加权。因此截断阶梯Legendre函数加权可以在保证CBT阵列性能的前提下有效减少阵元加权系数的数量。

Analysis of constant beamwidth array using stepped and truncated Legendre shading

A conventional constant beamwidth transducer CBT array using continuous Legendre shading achieves frequency-independent beam pattern at a particular frequency band using frequency-independent element weightings. However, it is necessary to assign individual weighting to every array element, and the complexity increases significantly while the element number is larger. Thus, the stepped and truncated Legendre shading is applied to various two-dimensional arrays, including spherical array, cylindrical array and planar array. Both spherical and cylindrical Legendre shading methods are analyzed. The results indicate that the influence of stepped and truncated Legendre shading on the beam direction is negligible, and the stepped and truncated Legendre shading mainly affects the beamwidth. In the cases of the two-dimensional arrays, the stepped and truncated Legendre shading achieves good approximation to the conventional continuous Legendre shading when the step is not greater than 3 dB and the truncation is not greater than ?21 dB. It is concluded that the stepped and truncated Legendre shading reduces the number of element weightings effectively.