Frequency invariant MVDR beamforming without filters and implementation using MIMO radar

Abstract

Abstract-Frequency invariant beamforming with sensor arrays is generally achieved using filters in the form of tapped delay-lines following each sensor. However it has been recently shown that with the help of the rectangular smart antenna array, it is possible to generate frequency invariant beampattern without using filters. In this paper, this frequency invariant beamforming technique is utilized to perform MVDR beamforming in the beamspace by designing frequency invariant beams spanning the desired range of azimuthal angles and optimally combining them. However the performance of the frequency invariant beamformer depends on the number of sensors which could be large for a rectangular array of size M × N . Making use of the virtual array concept used in MIMO radar, a novel method of producing the same frequency invariant beam, using only M transmitting and N receiving antennas, is proposed and a design example is provided to demonstrate the idea.

MIMO radar with broadband waveforms: Smearing filter banks and 2D virtual arrays

“…The viewpoint taken in this paper is that the wideband property is a nuisance which needs to be overcome before beamforming; so only a narrow region of the band is retained in the beamforming. If the wideband signals are information bearing, then the approach in [9] is more appropriate. …”

“…Since these arrays can be rendered frequency invariant by the use of smearing filters, they can perform two dimensional beamforming unlike [5], where the 2D array is used to perform frequency invariant beamforming in only one dimension. An altogether different technique to exploit the virtual array concept in the broadband case is reported in [9] which uses orthogonal waveforms sm(t) in different frequency bands. In this case there is no need for the smearing filters.…”

Frequency-Invariant Beamforming with Real FIR-filters

“…To achieve wideband characteristics of an array, it is necessary to use filters with finite impulse response (FIRfilters) [2], [5] that implement frequency dependent weight vector. Some techniques of frequency-invariant beamforming are based on usage of additional array elements [2], [6]. It should be noted that these methods are equivalent (i.e.…”

“…in both cases we should to form frequency dependent weight vector). Some of these techniques are based on a minimization problem solution [5], [6] and the other ones are required a Fourier transform [7]- [9].…”

A beamforming method for cylindrical array based on synthetic pattern of subarray

“…Conventional approaches of Beamforming for ULA are relatively mature, such as least mean square(LMS) algorithm [5][6], recursive least square(RLS) [7][8] algorithm, MVDR [9][10][11] algorithm, and other combined algorithms [12][13][14]. The LMS or RLS are two commonly used algorithms for beamforming.…”