I would suggest you looking at phased.Collector to collect signal and phased.ReceiverPreamp to add noise. Say you have a signal, x, of power 1 coming from 10 degrees azimuth and 20 degrees elevation. Assume you array is given by myArray and SNR is given by snr, it would look like
myCollector = phased.Collector('Sensor',myArray);
myPreamp = phased.ReceiverPreamp('Gain',0,'NoiseMethod','Noise power','NoisePower',10^(-snr/10));
Note the above two lines set up the components and you may need to adjust other parameters in myCollector like the frequencies. After that, to get the signal, you just need to do
y_collected = step(myCollector,x,[10;20]);
y_noiseadded = step(myPreamp,y_collected);
As name suggested, the first line collects the signal and the second line adds the noise.
HTH
