Distribution in space concept
The angular spacing between the beams in the fan can be controlled in one of three alternatives. The alternatives are Linear, Optimized, or Manual mode using the Beam Spacing Alternative parameter.
Linear mode distributes the beams in the fan with an equal spacing as given by the Beam Spacing Linear parameter. In special cases where the Beam Spacing Linear parameter is set to 0 degrees, all beams point in the same direction.
Optimized mode distributes the beams in the fan with an equal spacing in the k-domain. The width in the k-domain is calculated according to the Beam Spacing Optimized parameter (e.g. —3 dB one way). Combining this beam width from the k-domain with the frequency of each beam and the athwart ship centre angle of the fan, the beams are distributed in space
In Manual mode the steering angle of the individual beam is entered in the beam mode XML description file.
If you steer the beams to the outer limits of what the Beam Mode dialog allows, you must pay special attention in order to avoid repeated main lobes (aliasing). The following equation shows the maximum athwart steering angle, given the frequency of the beam and sound velocity.
= asin(1/ay —1)
The plot below shows the maximum athwart steering angle as a function of the beam frequency for a set of sound velocities.
Image
Several combinations of wide beam steering in modes with many beams may generate warning messages. In these cases, the system will limit the beam steering, compared to the operator request, and issue the warning message.