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Differential nullforming with uniform circular array

In almost all applications of beamforming, there is a requirement to form a null in a articular direction corresponding to noise sources like fans, air conditioners or heating vents. An m^{th} order differential beamforming is possible if the null direction is known apriori, m < N-1. It should be noted that even though differential beamforming produces narrow beamwidth pickups, the parameters can be chosen to ensure that all the desired beam directions are picked up without undue attenuation.

Consider a far field source impinging N UCA microphones as shown in Figure 1:

 

N UCA microphones

Figure 1: N UCA microphones

For example, for a 16 microphone, circular array, a 9^th order differential array can be used to produce the beam pattern shown in Figure 2 below.

Beam pattern at ∼ 2kHz

Figure 2: Beam pattern at \sim 2kHz

As shown in Figure 2, the beamwidth is about 240^{\circ} whilst a deep null is formed at the desired direction.

As a custom design house, VOCAL Technologies offers custom designed solutions for beamforming with a robust voice activity detector, acoustic echo cancellation and noise suppression. Our custom implementations of such systems are meant to deliver optimum performance for your specific beamforming task. Contact us today to discuss your solution!

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713
Email: sales@vocal.com