System object: phased.SubbandPhaseShiftBeamformer
Beamforming using subband phase shifting
Y = step(H,X)
Y = step(H,X,ANG)
[Y,W] = step(___)
[Y,FREQ] = step(___)
[Y,W,FREQ] = step(___)
Starting in R2016b, instead of using the
to perform the operation defined by the System object™, you can
call the object with arguments, as if it were a function. For example,
= step(obj,x) and
y = obj(x) perform
[ returns beamforming weights and
center frequencies of subbands. This syntax is available when you
WeightsOutputPort property to
SubbandsOutputPort property to
The object performs an initialization the first time the object is executed. This
initialization locks nontunable properties
and input specifications, such as dimensions, complexity, and data type of the input data.
If you change a nontunable property or an input specification, the System object issues an error. To change nontunable properties or inputs, you must first
release method to unlock the object.
Input signal, specified as an M-by-N matrix. If the sensor array contains subarrays, N is the number of subarrays; otherwise, N is the number of elements. This argument can be specified as single or double precision.
The size of the first dimension of the input matrix can vary to simulate a changing signal length. A size change can occur, for example, in the case of a pulse waveform with variable pulse repetition frequency.
Beamforming directions, specified as a two-row matrix. Each column 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 argument can be specified as single or double precision.
Center frequencies of subbands.
Apply subband phase-shift beamforming to an 11-element underwater ULA. The incident angle of a wideband signal is 10° in azimuth and 30° in elevation. The carrier frequency is 2 kHz.
Create the ULA.
antenna = phased.ULA('NumElements',11,'ElementSpacing',0.3); antenna.Element.FrequencyRange = [20 20000];
Create a chirp signal with noise.
fs = 1e3; carrierFreq = 2e3; t = (0:1/fs:2)'; x = chirp(t,0,2,fs); c = 1500; collector = phased.WidebandCollector('Sensor',antenna, ... 'PropagationSpeed',c,'SampleRate',fs,... 'ModulatedInput',true,'CarrierFrequency',carrierFreq); incidentAngle = [10;30]; x = collector(x,incidentAngle); noise = 0.3*(randn(size(x)) + 1j*randn(size(x))); rx = x + noise;
Beamform in the direction of the incident angle.
beamformer = phased.SubbandPhaseShiftBeamformer('SensorArray',antenna, ... 'Direction',incidentAngle,'OperatingFrequency',carrierFreq, ... 'PropagationSpeed',c,'SampleRate',fs,'SubbandsOutputPort',true, ... 'WeightsOutputPort',true); [y,w,subbandfreq] = beamformer(rx);
Plot the real part of the original and beamformed 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 the response pattern for five frequency bands.
pattern(antenna,subbandfreq(1:5).',[-180:180],0,'PropagationSpeed',c, ... 'CoordinateSystem','rectangular','Weights',w(:,1:5)) legend('location','SouthEast')
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 .
 Van Trees, H. Optimum Array Processing. New York: Wiley-Interscience, 2002.