Constant Directivity Beamforming

  • Darren B. Ward
  • Rodney A. Kennedy
  • Robert C. Williamson
Part of the Digital Signal Processing book series (DIGSIGNAL)


Beamforming, or spatial filtering, is one of the simplest methods for discriminating between different signals based on the physical location of the sources. Because speech is a very wideband signal, covering some four octaves, traditional narrowband beamforming techniques are inappropriate for hands-free speech acquisition. One class of broadband beamformers, called constant directivity beam-formers, aim to produce a constant spatial response over a broad frequency range. In this chapter we review such beamformers, and discuss implementation issues related to their use in microphone arrays.


Spatial Response Microphone Array Array Geometry Constant Directivity Spatial Aliasing 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. 1.
    B.D. Van Veen and K.M. Buckley, “Beamforming: A versatile approach to spatial filtering,” IEEE ASSP Mag., vol. 5, no. 2, pp. 4–24, Apr. 1988.CrossRefGoogle Scholar
  2. 2.
    T.D. Abhayapala, R.A. Kennedy, and R.C. Williamson, “Nearfield broadband array design using a radially invariant modal expansion,” J. Acoust. Soc. Amer., vol. 107, no. 1, pp. 392–403, Jan. 2000.CrossRefGoogle Scholar
  3. 3.
    J.L. Flanagan, D.A. Berkeley, G.W. Elko, J.E. West, and M.M. Sondhi, “Autodirective microphone systems,” Acustica, vol. 73, pp. 58–71, 1991.Google Scholar
  4. 4.
    W. Kellermann, “A self-steering digital microphone array,” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing (ICASSP-91), 1991, vol. 5, pp. 3581–3584.Google Scholar
  5. 5.
    F. Khalil, J.P. Jullien, and A. Gilloire, “Microphone array for sound pickup in teleconference systems,” J. Audio Eng. Soc., vol. 42, no. 9, pp. 691–700, Sept. 1994.Google Scholar
  6. 6.
    J. Lardies, “Acoustic ring array with constant beamwidth over a very wide frequency range,” Acoust. Letters, vol. 13, no. 5, pp. 77–81, 1989.Google Scholar
  7. 7.
    R. Smith, “Constant beamwidth receiving arrays for broad band sonar systems,” Acustica, vol. 23, pp. 21–26, 1970.Google Scholar
  8. 8.
    M.M. Goodwin and G.W. Elko, “Constant beamwidth beamforming,” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing (ICASSP-93), 1993, vol. 1, pp. 169–172.Google Scholar
  9. 9.
    J.H. Doles III and F.D. Benedict, “Broad-band array design using the asymptotic theory of unequally spaced arrays,” IEEE Trans. Antennas Propagat., vol. 36, no. 1, pp. 27–33, Jan. 1988.CrossRefGoogle Scholar
  10. 10.
    A. Ishimaru, “Theory of unequally-spaced arrays,” IRE Trans. Antennas Propagat., vol. AP-10, pp. 691–702, Nov. 1962.Google Scholar
  11. 11.
    A. Ishimaru and Y.S. Chen, “Thinning and broadbanding antenna arrays by unequal spacings,” IEEE Trans. Antennas Propagat., vol. AP-13, pp. 34–42, Jan. 1965.Google Scholar
  12. 12.
    T. Chou, “Frequency-independent beamformer with low response error,” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing (ICASSP-95), Detroit, USA, May 1995, pp. 2995–2998.Google Scholar
  13. 13.
    S. Haykin and J. Kesler, “Relation between the radiation pattern of an array and the two-dimensional discrete Fourier transform,” IEEE Trans. Antennas Propagat., vol. AP-23, no. 3, pp. 419–420, May 1975.Google Scholar
  14. 14.
    J.S. Marciano Jr. and T.B. Vu, “Reduced complexity beam space broadband frequency invariant beamforming,” Electronics Letters, vol. 36, no. 7, pp. 682683; Mar. 2000.Google Scholar
  15. 15.
    D.B. Ward, R.A. Kennedy, and R.C. Williamson, “Theory and design of broadband sensor arrays with frequency invariant far-field beam patterns,” J. Acoust. Soc. Amer., vol. 97, no. 2, pp. 1023–1034, Feb. 1995.MathSciNetCrossRefGoogle Scholar
  16. 16.
    D.B. Ward, R.A. Kennedy, and R.C. Williamson, “FIR filter design for frequency-invariant beamformers,” IEEE Signal Processing Lett., vol. 3, no. 3, pp. 69–71, Mar. 1996.CrossRefGoogle Scholar
  17. 17.
    C. Winter, “Using continuous apertures discretely,” IEEE Trans. Antennas Propagat., vol. AP-25, pp. 695–700, Sept. 1977.Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2001

Authors and Affiliations

  • Darren B. Ward
    • 1
  • Rodney A. Kennedy
    • 2
  • Robert C. Williamson
    • 2
  1. 1.Technology and MedicineImperial College of ScienceLondonUK
  2. 2.The Australian National UniversityCanberraAustralia

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