Design Of Frequency Invariant Beamformers Research Articles

Design and implementation of a rectangular frequency invariant beamformer with a full azimuth angle coverage

A novel design of the frequency invariant beamformer based on a rectangular array is proposed with two unique features: there are no taped delay-lines (TDLs) or any other temporal processing involved and the resultant beamformer has a full 360° azimuth angle coverage. This leads to a wideband beamformer with complex-valued coefficients and its implementation is not as straightforward as the traditional ones. Depending on whether the input signal is complex-valued or real-valued, special arrangements and structures are required for its effective implementation. Several design examples are provided with a satisfactory frequency invariant property. Two sets of implementation results are given based on both simulations and data collected by a planar microphone array system.

Subband design of fixed wideband beamformers based on the least squares approach

Subband method is an effective way to reduce the computational complexity of a wideband system and in this paper we study the subband design problem for fixed wideband beamformers, with an emphasis on the design of frequency invariant beamformers (FIBs). We first express the equivalent fullband beam response as a function of the subband beamformer coefficients and then formulate the design problem based on the least squares approach. One direct least squares formulation is first proposed for the design of a general wideband beamformer, and then extended to the FIB design case, followed by three further variations.

Design of Frequency Invariant Beamformer Without Temporal Filtering

A novel method for the design of frequency invariant beamformers for uniformly spaced three-dimensional (3-D) arrays is proposed. Unlike the traditional method, which is based on the use of temporal filtering, the proposed design can achieve a frequency invariant response without employing any temporal filtering process and the resultant beamformer does not suffer from the beam broadening effect at high off-boresight steering angles. A design example is provided to show the effectiveness of the proposed method.

Off-broadside main beam design and subband implementation for a class of frequency invariant beamformers

The design of frequency invariant beamformers (FIBs) with off-broadside main beams is studied and it is shown that the required FIR filter length in this case should be much larger than the one with a broadside main beam. To reduce the computational complexity of such a beamformer and also improve its frequency invariant property at lower frequencies, two subband implementations are proposed. In the first one, the fullband array signals are split into subbands by a bank of analysis filters and the corresponding decimated subband signals form a series of subband arrays. Based on this standard subband structure, we then change the sensor spacings of different subband signals so that lower frequency bands have a larger spacing, which leads to a class of FIBs with scaled aperture with further improved performance at lower frequencies.

Design of Frequency Invariant Beamformers for Broadband Arrays

A simple method for the design of a class of arrays with frequency invariant beam patterns is proposed. Starting from the desired frequency invariant beam pattern of an n-D array, the proposed method uses a series of substitutions and an n-D inverse Fourier transform to obtain the desired frequency responses of the filters following each sensor. Given their desired frequency responses, these filters can be realized by either an analogue filter or a digital filter. Hence the proposed method can cover the design of broadband arrays with either analogue signals or discrete signals. Two design examples are provided, with one for a linear array and one for a planar array.