Main Content

arrayfactor

Array factor of sensor arrays

    Description

    example

    af = arrayfactor(pos,ang) returns the array factor af for an array of elements located at positions pos and arrival directions ang.

    example

    af = arrayfactor(pos,ang,wts) also specifies array steering weights wts.

    Examples

    collapse all

    Compute the array factor for an unsteered 8-element ULA operating at 100 MHz. Elements are placed 0.4 wavelengths apart.

    freq = 100e6;
    c = physconst('LightSpeed');
    lam = c/freq;
    pos = (0:7)*0.4;
    ang = -90:90;
    af = arrayfactor(pos,ang);
    plot(ang,mag2db(abs(af.')))
    xlabel('Angle (deg)')
    ylabel('Array pattern (dB)')
    ylim([-30 20])
    title('Array Factor of Unsteered Uniform Linear Array')

    Display the array beam patterns for an 8-element ULA with half-wavelength spacing. Steer the array to -30, 0, and 30 degrees.

    Set the positions of the ULA elements.

    pos = (0:7)*0.5;

    Define the steering direction weights.

    angsteer = [-30 0 30];
    wsteer = steervec(pos,angsteer);

    Compute the array factors for each steering direction for all angles.

    ang = -90:90;
    af = arrayfactor(pos,ang,wsteer);

    Plot the array factor for each steering direction.

    plot(ang,mag2db(abs(af.')))
    xlabel('Angle (deg)')
    ylabel('Beam pattern (dB)')
    ylim([-50 20])
    legend('Steer to -30 deg','Steer to 0 deg','Steer to 30 deg')

    Input Arguments

    collapse all

    Positions of the elements of a sensor array specified as a 1-by-N vector, a 2-by-N matrix, or a 3-by-N matrix. In this vector or matrix, N represents the number of elements of the array. Each column of pos represents the coordinates of an element. If pos is a 1-by-N vector, then it represents the y-coordinate of the sensor elements of a line array. The x and z-coordinates are assumed to be zero. When pos is a 2-by-N matrix, it represents the (y,z)-coordinates of the sensor elements of a planar array. This array is assumed to lie in the yz-plane. The x-coordinates are assumed to be zero. When pos is a 3-by-N matrix, then the array can have an arbitrary shape. Sensor positions are in terms of signal wavelength.

    Example: [0,0,0; 0.1,0.4,0.3; 1,1,1]

    Data Types: double

    Arrival directions of incoming signals specified as a 1-by-M vector or a 2-by-M matrix, where M is the number of incoming signals. If ang is a 2-by-M matrix, each column specifies the direction in azimuth and elevation of the incoming signal [az;el]. The azimuth angle must lie between –180° and 180° and the elevation angle must lie between –90° and 90°. The azimuth angle is the angle between the x-axis and the projection of the arrival direction vector onto the xy plane. It is positive when measured from the x-axis toward the y-axis. The elevation angle is the angle between the arrival direction vector and xy-plane. It is positive when measured towards the z axis. If ang is a 1-by-M vector, then it represents a set of azimuth angles with the elevation angles assumed to be zero. Angle units are specified in degrees.

    Example: [45;0]

    Data Types: double

    Array weights, specified as a complex-valued N-by-1 vector or complex-valued N-by-L matrix. Each column of wts corresponds to a different set of weights for the array. L is the number of weight sets.

    Data Types: double
    Complex Number Support: Yes

    Output Arguments

    collapse all

    Array factor of sensor array, returned as a 1-by-M complex-valued vector or L-by-M complex-valued matrix. Each column contains the array factor for a different set of weights wts. Each row corresponds to one of the angles specified in ang.

    References

    [1] Van Trees, Harry L. Detection, Estimation, and Modulation Theory. 4: Optimum Array Processing. Wiley, 2002.

    [2] Johnson, Don H. and D. Dudgeon. Array Signal Processing. Englewood Cliffs, NJ: Prentice Hall, 1993.

    [3] Van Veen, B.D. and K. M. Buckley. “Beamforming: A versatile approach to spatial filtering”

    Version History

    Introduced in R2022a