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phased.SubbandPhaseShiftBeamformer System object

Package: phased

Subband phase shift beamformer

Description

The SubbandPhaseShiftBeamformer object implements a subband phase shift beamformer.

To compute the beamformed signal:

  1. Define and set up your subband phase shift beamformer. See Construction.

  2. Call step to perform the beamforming operation according to the properties of phased.SubbandPhaseShiftBeamformer. The behavior of step is specific to each object in the toolbox.

Construction

H = phased.SubbandPhaseShiftBeamformer creates a subband phase shift beamformer System object™, H. The object performs subband phase shift beamforming on the received signal.

H = phased.SubbandPhaseShiftBeamformer(Name,Value) creates a subband phase shift beamformer object, H, with each specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN).

Properties

SensorArray

Sensor array

Sensor array specified as an array System object belonging to the phased package. A sensor array can contain subarrays.

Default: phased.ULA with default property values

PropagationSpeed

Signal propagation speed

Specify the propagation speed of the signal, in meters per second, as a positive scalar.

Default: Speed of light

OperatingFrequency

System operating frequency

Specify the operating frequency of the beamformer in hertz as a scalar. The default value of this property corresponds to 300 MHz.

Default: 3e8

SampleRate

Signal sampling rate

Specify the signal sampling rate (in hertz) as a positive scalar.

Default: 1e6

NumSubbands

Number of subbands

Specify the number of subbands used in the subband processing as a positive integer.

Default: 64

DirectionSource

Source of beamforming direction

Specify whether the beamforming direction for the beamformer comes from the Direction property of this object or from an input argument in step. Values of this property are:

'Property'The Direction property of this object specifies the beamforming direction.
'Input port'An input argument in each invocation of step specifies the beamforming direction.

Default: 'Property'

Direction

Beamforming directions

Specify the beamforming directions of the beamformer as a two-row matrix. Each column of the matrix has the form [AzimuthAngle; ElevationAngle] (in degrees). Each azimuth angle must be between –180 and 180 degrees, and each elevation angle must be between –90 and 90 degrees. This property applies when you set the DirectionSource property to 'Property'.

Default: [0; 0]

WeightsOutputPort

Output beamforming weights

To obtain the weights used in the beamformer, set this property to true and use the corresponding output argument when invoking step. If you do not want to obtain the weights, set this property to false.

Default: false

SubbandsOutputPort

Output subband center frequencies

To obtain the center frequencies of each subband, set this property to true and use the corresponding output argument when invoking step. If you do not want to obtain the center frequencies, set this property to false.

Default: false

Methods

cloneCreate subband phase shift beamformer object with same property values
getNumInputsNumber of expected inputs to step method
getNumOutputsNumber of outputs from step method
isLockedLocked status for input attributes and nontunable properties
releaseAllow property value and input characteristics changes
stepBeamforming using subband phase shifting

Examples

Apply subband phase shift beamformer to an 11-element ULA. The incident angle of the signal is 10 degrees in azimuth and 30 degrees in elevation.

% Signal simulation
ha = phased.ULA('NumElements',11,'ElementSpacing',0.3);
ha.Element.FrequencyRange = [20 20000];
fs = 1e3; carrierFreq = 2e3; t = (0:1/fs:2)';
x = chirp(t,0,2,fs);
c = 1500; % Wave propagation speed (m/s)
hc = phased.WidebandCollector('Sensor',ha,...
    'PropagationSpeed',c,'SampleRate',fs,...
    'ModulatedInput',true,'CarrierFrequency',carrierFreq);
incidentAngle = [10; 30];
x = step(hc,x,incidentAngle);
noise = 0.3*(randn(size(x)) + 1j*randn(size(x)));
rx = x+noise;

% Beamforming
hbf = phased.SubbandPhaseShiftBeamformer('SensorArray',ha,...
    'Direction',incidentAngle,...
    'OperatingFrequency',carrierFreq,'PropagationSpeed',c,...
    'SampleRate',fs,'SubbandsOutputPort',true,...
    'WeightsOutputPort',true);
[y,w,subbandfreq] = step(hbf,rx);

% Plot signals
plot(t(1:300),real(rx(1:300,6)),'r:',t(1:300),real(y(1:300)));
xlabel('Time'); ylabel('Amplitude');
legend('Original','Beamformed');

% Plot response pattern for five bands
figure;
plotResponse(ha,subbandfreq(1:5).',c,'Weights',w(:,1:5));
legend('location','SouthEast')

Algorithms

The subband phase shift beamformer separates the signal into several subbands and applies narrowband phase shift beamforming to the signal in each subband. The beamformed signals in all the subbands are regrouped to form the output signal.

For further details, see [1].

References

[1] Van Trees, H. Optimum Array Processing. New York: Wiley-Interscience, 2002.

See Also

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