phased.WidebandCollector

Wideband signal collector

Description

The phased.WidebandCollector System object™ implements a wideband signal collector. A collector converts incident wideband wave fields arriving from specified directions into signals to be further processed. Wave fields are incident on antenna and microphone elements, sensor arrays, or subarrays. The object collects signals in one of two ways controlled by the Wavefront Wavefront property.

• If the Wavefront property is set to 'Plane', the collected signals at each element or subarray are the coherent sum of all incident plane wave fields sampled at each array element or subarray.

• If the Wavefront property is set to 'Unspecified', the collected signals are formed from an independent field incident on each individual sensor element.

You can use this object to

• model arriving signals as polarized or non-polarized fields depending upon whether the element or array supports polarization and the value of the Polarization property. Using polarization, you can receive a signal as a polarized electromagnetic field, or receive two independent signals using orthogonal polarization directions.

• model acoustic fields by using nonpolarized microphone and sonar transducer array elements and by setting the Polarization to 'None'. You must also set the PropagationSpeed to a value appropriate for the medium.

• collect fields at subarrays created by the phased.ReplicatedSubarray and phased.PartitionedArray objects. You can steer all subarrays in the same direction using the steering angle argument, STEERANG, or steer each subarray in a different direction using the subarray element weights argument, WS. You cannot set the Wavefront property to 'Unspecified' for subarrays.

To collect arriving signals at the elements or arrays:

1. Create the phased.WidebandCollector object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

collector = phased.WidebandCollector

collector = phased.WidebandCollector(Name,Value)

Description

collector = phased.WidebandCollector creates a wideband signal collector object, collector, with default property values.

collector = phased.WidebandCollector(Name,Value) creates a wideband signal collector with each property Name set to a specified Value. You can specify additional name-value pair arguments in any order as (Name1,Value1,...,NameN,ValueN). Enclose each property name in single quotes.

Example: collector = phased.WidebandCollector('Sensor',phased.URA,'CarrierFrequency',300e6) sets the sensor array to a uniform rectangular array (URA) with default URA property values. The beamformer assumes a carrier frequency of 300 MHz.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

Sensor — Sensor element or sensor array

phased.ULA array with default property values (default) | Phased Array System Toolbox™ sensor or array

Sensor element or sensor array, specified as a System object belonging to Phased Array System Toolbox. A sensor array can contain subarrays.

Example: phased.URA

PropagationSpeed — Signal propagation speed

physconst('LightSpeed') (default) | positive scalar

Signal propagation speed, specified as a positive scalar. Units are in meters per second. The default propagation speed is the value returned by physconst('LightSpeed'). See physconst for more information.

Example: 3e8

Data Types: double

SampleRate — Signal sample rate

1e6 (default) | positive real-valued scalar

Signal sample rate, specified as a positive real-valued scalar. Units are in hertz.

Example: 1e6

Data Types: double

ModulatedInput — Assume modulated input

true (default) | false

Set this property to true to indicate the input signal is demodulated at a carrier frequency.

Data Types: logical

CarrierFrequency — Carrier frequency

1e9 (default) | positive real-valued scalar

Carrier frequency, specified as a positive real-valued scalar. Units are in hertz.

Example: 1e6

Data Types: double

NumSubbands — Number of processing subbands

64 (default) | positive integer

Number of processing subbands, specified as a positive integer.

Example: 128

Data Types: double

SensorGainMeasure — Specify sensor gain

'dB' (default) | 'dBi'

Sensor gain measure, specified as 'dB' or 'dBi'.

• When you set this property to 'dB', the input signal power is scaled by the sensor power pattern (in dB) at the corresponding direction and then combined.

• When you set this property to 'dBi', the input signal power is scaled by the directivity pattern (in dBi) at the corresponding direction and then combined. This option is useful when you want to compare results with the values predicted by the radar equation that uses dBi to specify the antenna gain. The computation using the 'dBi' option is expensive as it requires an integration over all directions to compute the total radiated power of the sensor.

Data Types: char

Wavefront — Type of incoming wavefront

'Plane' (default) | 'Unspecified'

The type of incoming wavefront, specified as 'Plane' or 'Unspecified':

• 'Plane' — input signals are multiple plane waves impinging on the entire array. Each plane wave is received by all collecting elements.

• 'Unspecified' — collected signals are independent fields incident on individual sensor elements. If the Sensor property is an array that contains subarrays, you cannot set the Wavefront property to 'Unspecified'.

Data Types: char

Polarization — Polarization configuration

'None' (default) | 'Combined' | 'Dual'

Polarization configuration, specified as 'None', 'Combined', or 'Dual'. When you set this property to 'None', the incident fields are considered scalar fields. When you set this property to 'Combined', the incident fields are polarized and represent a single arriving signal whose polarization reflects the sensor's inherent polarization. When you set this property to 'Dual', the H and V polarization components of the fields are independent signals.

Example: 'Dual'

Data Types: char

WeightsInputPort — Enable weights input

false (default) | true

Enable weights input, specified as false or true. When true, use the object input argument W to specify weights. Weights are applied to individual array elements (or at the subarray level when subarrays are supported).

Data Types: logical

Usage

Syntax

Y = collector(X,ANG)

Y = collector(X,ANG,LAXES)

[YH,YV] = collector(X,ANG,LAXES)

[___] = collector(___,W)

[___] = collector(___,STEERANG)

[___] = collector(___,WS)

Description

Y = collector(X,ANG) collects the signals, X, arriving from the directions specified by ANG. Y contains the collected signals.

Y = collector(X,ANG,LAXES) also specifies LAXES as the local coordinate system axes directions. To use this syntax, set the property to 'Combined'.

[YH,YV] = collector(X,ANG,LAXES) returns an H-polarization component of the field, YH, and a V-polarization component, YV. To use this syntax, set the Polarization property to 'Dual'.

[___] = collector(___,W) also specifies W as array element or subarray weights. To use this syntax, set the WeightsInputPort property to true.

[___] = collector(___,STEERANG) also specifies STEERANG as the subarray steering angle. To use this syntax, set the Sensor property to an array that supports subarrays and set the SubarraySteering property of that array to either 'Phase' or 'Time'.

[___] = collector(___,WS) also specifies WS as the weights applied to each element within each subarray. To use this syntax, set the Sensor property to an array that supports subarrays and set the SubarraySteering of that array to 'Custom'.

Input Arguments

X — Arriving signals

complex-valued M-by-L matrix | complex-valued 1-by-L cell array of structures

Arriving signals, specified as a complex-valued M-by-L matrix or complex-valued 1-by-L cell array of structures. M is the number of signal samples and L is the number of arrival angles. This argument represents the arriving fields.

• If the Polarization property value is set to 'None', X is an M-by-L matrix.

• If the Polarization property value is set to 'Combined' or 'Dual', X is a 1-by-L cell array of structures. Each cell corresponds to a separate arriving signal. Each struct contains three column vectors containing the X, Y, and Z components of the polarized fields defined with respect to the global coordinate system.

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.

Dependencies

To enable this argument, set the Polarization property to 'None' or 'Combined'.

Data Types: double
Complex Number Support: Yes

ANG — Arrival directions of signals

real-valued 2-by-L matrix

Arrival directions of signals, specified as a real-valued 2-by-L matrix. Each column specifies an arrival direction in the form [AzimuthAngle;ElevationAngle]. The azimuth angle must lie between –180° and 180°, inclusive. The elevation angle must lie between –90° and 90°, inclusive. When the Wavefront property is false, the number of angles must equal the number of array elements, N. Units are in degrees.

Example: [30,20;45,0]

Data Types: double

LAXES — Local coordinate system

real-valued 3-by-3 orthogonal matrix

Local coordinate system, specified as a real-valued 3-by-3 orthogonal matrix. The matrix columns specify the local coordinate system's orthonormal x, y, and z axes with respect to the global coordinate system.

Example: rotx(30)

Dependencies

To enable this argument, set the Polarization property to 'Combined' or 'Dual'.

Data Types: double

W — Element or subarray weights

N-by-1 column vector

Element or subarray weights, specified as a complex-valued N-by-1 column vector where N is the number of array elements (or subarrays when the array supports subarrays).

Dependencies

To enable this argument, set the WeightsInputPort property to true.

Data Types: double
Complex Number Support: Yes

WS — Subarray element weights

complex-valued N_SE-by-N matrix | 1-by-N cell array

Subarray element weights, specified as complex-valued N_SE-by-N matrix or 1-by-N cell array where N is the number of subarrays. These weights are applied to the individual elements within a subarray.

Subarray element weights

Sensor Array	Subarray weights
phased.ReplicatedSubarray	All subarrays have the same dimensions and sizes. Then, the subarray weights form an NSE-by-N matrix. NSE is the number of elements in each subarray and N is the number of subarrays. Each column of WS specifies the weights for the corresponding subarray.
phased.PartitionedArray	Subarrays may not have the same dimensions and sizes. In this case, you can specify subarray weights as an NSE-by-N matrix, where NSE is now the number of elements in the largest subarray. The first Q entries in each column are the element weights for the subarray where Q is the number of elements in the subarray. a 1-by-N cell array. Each cell contains a column vector of weights for the corresponding subarray. The column vectors have lengths equal to the number of elements in the corresponding subarray.

Dependencies

To enable this argument, set the Sensor property to an array that contains subarrays and set the SubarraySteering property of the array to 'Custom'.

Data Types: double
Complex Number Support: Yes

STEERANG — Subarray steering angle

real-valued 2-by-1 vector

Subarray steering angle, specified as a length-2 column vector. The vector has the form [azimuthAngle;elevationAngle]. The azimuth angle must be between –180° and 180°, inclusive. The elevation angle must be between –90° and 90°, inclusive. Units are in degrees.

Example: [20;15]

Dependencies

To enable this argument, set the Sensor property to an array that supports subarrays and set the SubarraySteering property of that array to either 'Phase' or 'Time'

Data Types: double

Output Arguments

Y — Collected signal

complex-valued M-by-N matrix

Collected signal, returned as a complex-valued M-by-N matrix. M is the length of the input signal. N is the number of array elements (or subarrays when subarrays are supported). Each column corresponds to the signal collected by the corresponding array element (or corresponding subarrays when subarrays are supported).

Dependencies

To enable this argument, set the Polarization property to 'None' or 'Combined'.

Data Types: double
Complex Number Support: Yes

YH — Collected horizontal polarization signal

complex-valued M-by-N matrix

Collected horizontal polarization signal, returned as a complex-valued M-by-N matrix. M is the length of the input signal. N is the number of array elements (or subarrays when subarrays are supported). Each column corresponds to the signal collected by the corresponding array element (or corresponding subarrays when subarrays are supported).

Dependencies

To enable this argument, set the Polarization property to 'Dual'.

Data Types: double
Complex Number Support: Yes

YV — Collected vertical polarization signal

complex-valued M-by-N matrix

Collected horizontal polarization signal, returned as a complex-valued M-by-N matrix. M is the length of the input signal. N is the number of array elements (or subarrays when subarrays are supported). Each column corresponds to the signal collected by the corresponding array element (or corresponding subarrays when subarrays are supported).

Dependencies

To enable this argument, set the Polarization property to 'Dual'.

Data Types: double
Complex Number Support: Yes

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Collect Wideband Signal at Single Antenna

Use the phased.WidebandCollector System object™ to construct a signal arriving at a single isotropic antenna from 10° azimuth and 30° elevation.

antenna = phased.IsotropicAntennaElement;
collector = phased.WidebandCollector('Sensor',antenna);
x = [1;0;-1];
incidentAngle = [10;30];
y = collector(x,incidentAngle);
disp(y)

   1.0000 + 0.0000i
   0.0000 + 0.0000i
  -1.0000 - 0.0000i

Collect Wideband Signal at 5-Element ULA

Use the wideband collector to construct the signal impinging upon a 5-element ULA of isotropic antennas from 10 degrees azimuth and 30 degrees elevation.

array = phased.ULA('NumElements',5);
collector = phased.WidebandCollector('Sensor',array);
x = [1;1;1];
incidentAngle = [10;30];
y = collector(x,incidentAngle);
disp(y)

  -0.9997 + 0.0102i  -0.0051 - 0.9999i   1.0000 + 0.0000i  -0.0051 + 1.0001i  -1.0002 - 0.0102i
  -0.9999 + 0.0102i  -0.0051 - 1.0000i   1.0000 + 0.0000i  -0.0051 + 1.0000i  -0.9999 - 0.0102i
  -1.0002 + 0.0102i  -0.0051 - 1.0001i   1.0000 - 0.0000i  -0.0051 + 0.9999i  -0.9997 - 0.0102i

Collect Different Signals at 3-Element ULA

Collect three signals incoming into a 3-element array of isotropic antenna elements. Each antenna collects a separate input signal from a separate direction.

array = phased.ULA('NumElements',3);
collector = phased.WidebandCollector('Sensor',array,...
    'Wavefront','Unspecified');
rng default
x = rand(10,3);
incidentAngles = [10 20 45; 0 5 2];
y = collector(x,incidentAngles);
disp(y)

   0.8147 + 0.0000i   0.1576 + 0.0000i   0.6557 - 0.0000i
   0.9058 + 0.0000i   0.9706 + 0.0000i   0.0357 + 0.0000i
   0.1270 - 0.0000i   0.9572 + 0.0000i   0.8491 - 0.0000i
   0.9134 - 0.0000i   0.4854 + 0.0000i   0.9340 - 0.0000i
   0.6324 + 0.0000i   0.8003 + 0.0000i   0.6787 - 0.0000i
   0.0975 - 0.0000i   0.1419 + 0.0000i   0.7577 - 0.0000i
   0.2785 + 0.0000i   0.4218 - 0.0000i   0.7431 - 0.0000i
   0.5469 - 0.0000i   0.9157 - 0.0000i   0.3922 - 0.0000i
   0.9575 + 0.0000i   0.7922 + 0.0000i   0.6555 + 0.0000i
   0.9649 + 0.0000i   0.9595 + 0.0000i   0.1712 - 0.0000i

More About

Subband Frequency Processing

Subband processing decomposes a wideband signal into multiple subbands and applies narrowband processing to the signal in each subband. The signals for all subbands are summed to form the output signal.

When using wideband frequency System objects or blocks, you specify the number of subbands, N_B, in which to decompose the wideband signal. Subband center frequencies and widths are automatically computed from the total bandwidth and number of subbands. The total frequency band is centered on the carrier or operating frequency, f_c. The overall bandwidth is given by the sample rate, f_s. Frequency subband widths are Δf = f _s/N_B. The center frequencies of the subbands are

$$f_m=\{\begin{array}{c}{f}_c-\frac{f_s}{2}+\left(m-1\right)\Delta f\text{, }{N}_B\text{ even}\\ f_c-\frac{\left(N_B-1\right)f_s}{2N_B}+\left(m-1\right)\Delta f\text{, }{N}_B\text{ odd}\end{array},m=1,\dots ,N_B$$

Some System objects let you obtain the subband center frequencies as output when you run the object. The returned subband frequencies are ordered consistently with the ordering of the discrete Fourier transform. Frequencies above the carrier appear first, followed by frequencies below the carrier.

The phased.WidebandCollector System object uses the narrowband phased approximation of the time delays across receiving elements in the far field for each subband.

Algorithms

If the Wavefront property value is 'Plane', phased.WidebandCollector does the following for each plane wave signal:

1. Decomposes the signal into multiple subbands.

2. Uses the phase approximation of the time delays across collecting elements in the far field for each subband.

3. Regroups the collected signals in all the subbands to form the output signal.

If the Wavefront property value is 'Unspecified', the object collects each channel independently.

For further details, see [1].

References

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

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• Requires dynamic memory allocation. See Limitations for System Objects that Require Dynamic Memory Allocation.

• See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2011a