Frequency-Invariant Beam Steering Based on FIR-Filters
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uency-Invariant Beam Steering Based on FIR-Filters1 Alexey Erokhin*, Evgeniy Gafarov**, and Yury Salomatov*** Siberian Federal University, Krasnoyarsk, Russia *ORCID: 0000-0002-7707-8792, e-mail: [email protected] **ORCID: 0000-0002-7810-7196, e-mail: [email protected] ***ORCID: 0000-0003-4309-226X, e-mail: [email protected] Received December 30, 2019 Revised September 18, 2020 Accepted October 18, 2020
Abstract—Conventional narrowband beamforming methods are not effective for wideband antenna arrays. Radiation pattern of such array has various beam width over the frequency. Existing frequency-invariant beamforming methods using finite impulse response filters (FIR-filters) can solve this problem. FIR-filters provide frequency response required for frequency-independent properties of the array radiation pattern but their common feature is a high computational complexity. In this paper, we present the fixed frequency-invariant beamforming method that does not require minimizing functions or the Fourier transform. The beam steering is achieved by using FIR-filters with different slope of the frequency response. The proposed approach is based on the FIR-filters synthesis with special frequency characteristics. The numerical results compared with the existing frequency-invariant beamforming method are shown. DOI: 10.3103/S0735272720100027
1. INTRODUCTION Recently, the broadband beamforming is extensively studied by many researchers. Here we can distinguish a class of arrays with a frequency-invariant radiation pattern (RP) in a certain frequency band. As a frequency-invariant array we mean an array whose RP does not change over a wide frequency band, i.e. the level of side lobes and the half power beam width are nearly constant in the frequency band. There are many studies of microphone arrays used in acoustic applications like speech enhancement, recognition, hearing aid applications and direction finding [1]–[4]. In addition, frequency-invariant beamforming can be used in such areas as wireless communication, radar and sonar applications [5]–[8]. The finite impulse response filters (FIR-filters) allow us to achieve frequency-invariant characteristics of the array [6], [9]. In [10] authors note that the maintaining of the effective array aperture is necessary to keep a constant beam width in the frequency band. This can be achieved by FIR-filters for frequency dependent weight vector implementation, i.e. FIR-filters perform temporal filtering, and that gives a frequency dependent response. Some techniques of frequency-invariant beamforming are based on additional array elements using (beamforming with sensor delay-lines) [6], [11], [12]. The circular antenna arrays are used in frequency-invariant beamforming [8], [13], [14] as arrays with the spatial delay. In [15], the beamforming technique with the uniformly spaced three-dimensional array is used to achieve frequency-invariant properties. These methods may not always be appropriate in terms of practical implementation because of a large number of elements
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