Passive Beamformer Research Articles

A Precorrection Method for Passive UWB Time-Reversal Beamformer

The passive time-reversal beamformer is a 1 × N ports device with N orthogonal channels. Beamforming is achieved using simultaneous time reversal focusing on the output ports with the only input waveform. Utilizing this method, an antenna array can be supplied with focused signals of controlled complex weights and achieve beam steering. A precorrection method is developed in this letter to normalize the weights of the output signals at the focusing time, avoiding a long optimization step of beamformer designing. The theory is developed in this letter, followed by experimental validation.

UWB Antennas Beamforming Using Passive Time-Reversal Device

In this letter, the feasibility of a new concept of passive antenna beamformer is investigated. The main idea is to develop a (1×N)-ports device in which the weightings on output ports are applied by time-reversal operation. The control of antennas weightings is then contained in the input waveform without the need of active components or external control signals. This approach is validated experimentally by radiation pattern measurement of a four-Vivaldi-antennas array, associated to a small reverberation cell beamformer. Finally, this concept is applied to realize a passive ultrawideband (UWB) phased-array radar for target imaging.

Robust passive beamformer using bridge function sequences as weights

This letter introduces a novel passive beamformer which uses Bridge function sequence as spreading sequence weights for every antenna element. The set of Bridge function sequences have zero correlation zones (ZCZs) in their cross-correlation functions (CCFs). Due to the ZCZ properties of Bridge function sequences, the introduced passive beamformer features a much better performance on avoiding synchronization errors than the passive beamformers utilizing other spreading sequences without ZCZ.The theoretical justification of the proposed approach is presented in detail and the achievable performance is verified through computer simulations.

Passive hybrid subtractive beamformer for near-field sound sources

This paper describes the problem caused by near-field sound sources. Formerly, the authors proposed a 2-ch passive subtractive beamformer with a single sharp notch for noise reduction. It is obvious that the single sharp notch is insufficient for dealing with near-field, non-point sound sources. To solve this problem, this paper presents the hybrid subtractive beamformer that is realized as a cascade connection of single subtractive beamformers. The number of connections depends on frequency to minimize the negative effect caused by spatial aliasing when an objective signal is assumed as a wide-band speech signal. The experimental results verifies that the hybrid beamformer has an advantage in reducing signal distortion over the original single subtractive beamformer.

Passive subtractive beamformer applied to line sound sources

Speech is an attractive interface for mobile equipment if it is clearly received. A microphone array aids in reducing noise and enhancing speech. A small-scale microphone array generally adopts the subtractive beamforming technique, which constructs sharp notches in a beampattern in either an active or a passive way, so that target sound sources are assumed as point sound sources. However, the shapes of actual sound sources are various and not always points. In particular, the mouth needs to be modeled as line sound source or plane sound source. Therefore, beamformers should target line sound sources. A passive subtractive beamformer is proposed to expand width of a sharp notch by combining several 2ch subtractive beamformers. In multiple sound source conditions, it is necessary to avoid the effect of spatial aliasing against nontarget sound sources. Then, a hybrid technique is applied to realize an optimal connection of the quadruple, double, and single subtractive beamformer for the low, middle, and high frequency region. The feasibility of the proposed subtractive beamformer is confirmed by performance evaluation in suppressing the signals from line sound sources. [Work supported by the Telecommunications Advancement Organization of Japan.]

Passive beamformer with low side lobes

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