Does the Beamformer model structure model truncation errors that result when the desired gain and phase setting of the beamformer is in between the available discrete gain and time delay settings of the device.

Yes, when you are doing a SystemVue simulation of a beam pattern, SystemVue will calculate the ideal gain and time delay settings of each element. But these settings have to be quantized according to the available step sizes of the attenuator and time delay unit. The quantization error that results will be reflected in the resulting beam pattern.