step

System object: phased.ReplicatedSubarray
Package: phased

Output responses of subarrays

Syntax

RESP = step(H,FREQ,ANG,V)

RESP = step(H,FREQ,ANG,V,STEERANGLE)

RESP = step(H,FREQ,ANG,V,WS)

Description

Note

Starting in R2016b, instead of using the step method to perform the operation defined by the System object™, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

RESP = step(H,FREQ,ANG,V) returns the responses, RESP, of the subarrays in the array, at operating frequencies specified in FREQ and directions specified in ANG. V is the propagation speed. The elements within each subarray are connected to the subarray phase center using an equal-path feed.

RESP = step(H,FREQ,ANG,V,STEERANGLE) uses STEERANGLE as the steering direction of the subarray. This syntax is available when you set the SubarraySteering property to either 'Phase' or 'Time'.

RESP = step(H,FREQ,ANG,V,WS) uses WS as the subarray element weights. This syntax is available when you set the SubarraySteering property to 'Custom'.

Note

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 call the release method to unlock the object.

Input Arguments

H	Phased array formed by replicated subarrays.
FREQ	Operating frequencies of array in hertz. FREQ is a row vector of length L. Typical values are within the range specified by a property of H.Subarray.Element. That property is named FrequencyRange or FrequencyVector, depending on the type of element in the array. The element has zero response at frequencies outside that range.
ANG	Directions in degrees. ANG can be either a 2-by-M matrix or a row vector of length M. If ANG is a 2-by-M matrix, each column of the matrix specifies the direction in the form [azimuth; elevation]. The azimuth angle must be between –180 and 180 degrees, inclusive. The elevation angle must be between –90 and 90 degrees, inclusive. If ANG is a row vector of length M, each element specifies a direction’s azimuth angle. In this case, the corresponding elevation angle is assumed to be 0.
V	Propagation speed in meters per second. This value must be a scalar.
STEERANGLE	Subarray steering direction. STEERANGLE can be either a 2-element column vector or a scalar. If this argument is a 2-element column vector, it has the form [azimuth; elevation]. The azimuth angle must be between –180° and 180°, inclusive. The elevation angle must be between –90° and 90°, inclusive. If STEERANGLE is a scalar, it specifies the direction’s azimuth angle. In this case, the elevation angle is assumed to be 0°. Dependencies To enable this argument, set the SubarraySteering to 'Phase' or 'Time'.
WS	Subarray element weights Subarray element weights, specified as complex-valued NSE-by-N matrix. Weights are applied to the individual elements within a subarray. All subarrays have the same dimensions and sizes. NSE is the number of elements in each subarray and N is the number of subarrays. Each column of the matrix specifies the weights for the corresponding subarray. Dependencies To enable this argument, set the SubarraySteering to 'Custom'.

Output Arguments

RESP

Voltage responses of the subarrays of the phased array. The output depends on whether the array supports polarization or not. If the array is not capable of supporting polarization, the voltage response, RESP, has the dimensions N-by-M-by-L. The first dimension, N , represents the number of subarrays in the phased array, the second dimension, M, represents the number of angles specified in ANG, while L represents the number of frequencies specified in FREQ. Each column of RESP contains the responses of the subarrays for the corresponding direction specified in ANG. Each of the L pages of RESP contains the responses of the subarrays for the corresponding frequency specified in FREQ. If the array is capable of supporting polarization, the voltage response, RESP, is a MATLAB® struct containing two fields, RESP.H and RESP.V, each having dimensions N-by-M-by-L. The field, RESP.H, represents the array’s horizontal polarization response, while RESP.V represents the array’s vertical polarization response. The first dimension, N , represents the number of subarrays in the phased array, the second dimension, M, represents the number of angles specified in ANG, while L represents the number of frequencies specified in FREQ. Each of the M columns contains the responses of the subarrays for the corresponding direction specified in ANG. Each of the L pages contains the responses of the subarrays for the corresponding frequency specified in FREQ.

Examples

Subarray Response

Calculate the response at boresight for two 2-element ULA arrays that form subarrays of a 4-element ULA array of short-dipole antenna elements.

Create a two-element ULA of short-dipole antenna elements. Then, arrange two copies to form a 4-element ULA.

antenna = phased.ShortDipoleAntennaElement;
array = phased.ULA('Element',antenna,'NumElements',2,'ElementSpacing',0.5);
replicatedarray = phased.ReplicatedSubarray('Subarray',array,...
    'Layout','Rectangular','GridSize',[1 2],...
    'GridSpacing','Auto');

Find the response of each subarray at boresight. Assume the operating frequency is 1 GHz and the wave propagation speed is the speed of light.

c = physconst('LightSpeed');
resp = replicatedarray(1.0e9,[0;0],c)

resp = struct with fields:
    H: [2x1 double]
    V: [2x1 double]

Independently Steered Replicated Subarrays

Create an array consisting of three copies of a 4-element ULA having elements spaced 1/2 wavelength apart. The array operates at 300 MHz.

c = physconst('LightSpeed'); 
fc = 300e6;
lambda = c/fc;
subarray = phased.ULA(4,0.5*lambda);

Steer all subarrays by a common phase shift to 10 degrees azimuth.

array = phased.ReplicatedSubarray('Subarray',subarray,'GridSize',[1 3], ... 
    'SubarraySteering','Phase','PhaseShifterFrequency',fc); 
steer_ang = [10;0]; 
sv_array = phased.SteeringVector('SensorArray',array,... 
    'PropagationSpeed',c); 
wts_array = sv_array(fc,steer_ang);
pattern(array,fc,-90:90,0,'CoordinateSystem','Rectangular',... 
    'Type','powerdb','PropagationSpeed',c,'Weights',wts_array,... 
    'SteerAngle',steer_ang);
legend('phase-shifted subarrays')

Compute independent subarray weights from subarray steering vectors. The weights point to 5, 15, and 30 degrees azimuth. Set the SubarraySteering property to 'Custom' .

steer_ang_subarrays = [5 15 30;0 0 0];
sv_subarray = phased.SteeringVector('SensorArray',subarray,... 
    'PropagationSpeed',c);
wc = sv_subarray(fc,steer_ang_subarrays); 
array.SubarraySteering = 'Custom';
pattern(array,fc,-90:90,0,'CoordinateSystem','Rectangular',... 
    'Type','powerdb','PropagationSpeed',c,'Weights',wts_array,... 
    'ElementWeight',conj(wc)); 
legend('independent subarrays') 
hold off