How to define local refaxes in "rangeangle" function, when the local refaxes is moving with antenna phase array on the nose of an aircraft?

I want get Az/El angles wrt to antenna array local coordinate system, so that I can properly get relative phase relation bwteen elelemts in the array, using phased.collector.

The example "Waveform Parameter Extraction for Received Pulse" has

% Model the radar receiver chain---------------------------------------------------------

collector = phased.Collector('Sensor', antennaRx,'OperatingFrequency',fc);

rx = phased.ReceiverPreamp('Gain',0,'NoiseMethod','Noise power', 'NoisePower',2.5e-6,'SeedSource','Property', 'Seed',2018);

% Collect the waves at the receiver

[~, tgtAng] = rangeangle(radarPos,rwrPos);

yr = collector(txPulseTrain,tgtAng);

yr = rx(yr);

%-------------------------------------------------------------------------------------

it does not properly use rangeangle function, as the tgtAng is not reference to the RWR local coordinate system.

1. Can someone tell me in the example how do I get Az/El from antenna local coordinate system?
2. If the local coordinate system is at the center of a planer phase array, which is installed on the front of an aircraft and move with the aircraft, how do I define this local coordinate system which location and oriantation change with time, so that rangeangle can produce time-based range and Az/El wrt the local coordinate system?

Mnay thanks in advance!

Chen

Answer 1

[Garmit Pant]

Hello Chen Wu,

I understand that you are trying to find the Azimuth/Elevation angles with respect to the antenna array local coordinate system, but you are unable to extract these angles properly using the “rangeangle” function.

The “rangeangle” function can be utilised to find the propagation path length and path direction of a signal from a source point or set of source points to a reference point with respect to a local coordinate system. You need to specify the reference axes as a 3x3x3xN array where N is the number of reference points and each 3x3x3 page in the array corresponds to a local coordinate axes at each reference point. 

The following example highlights how to get the range and angle with respect to the local coordinates:

targetpos = [1000;2000;50]; 
origin = [100;100;10]; 
refaxes = [1/sqrt(2) -1/sqrt(2) 0; 1/sqrt(2) 1/sqrt(2) 0; 0 0 1]; 
[tgtrng,tgtang] = rangeangle(targetpos,origin,refaxes) 

tgtrng = 2.1028e+03

tgtang = 2×1

19.6538 1.0900

You can follow the following MATLAB example to model moving radars and calculations of angles and ranges with respect to moving local coordinates:

https://www.mathworks.com/help/phased/ug/local-and-global-coordinate-systems-example-in-radar.html

For more information, you can also refer to the following MATLAB Documentation:

1. Refer to the “Input Arguments” section to understand the input arguments and their properties- https://in.mathworks.com/help/phased/ref/rangeangle.html
2. Function to model translational motion of platforms in space - https://in.mathworks.com/help/phased/ref/phased.platform-system-object.html
3. Refer to “Input Arguments” section - https://in.mathworks.com/help/phased/ref/phased.collector-system-object.html

I hope you find the above explanation and suggestions useful.

Regards

Garmit