Linear mode
Linear mode provides three different options for linear spacing.
Default Linear mode
In Linear mode, the total band (B) is limited by upper and lower frequency limits. The band is equally divided between the beams in the fan, and any reference beams with a requested frequency inside the band (N). Some overlap in frequency is allowed by calculating:
Bfc = B/(N*0.85)
This 1/0.85 = 1.18 means that the upper and lower 9% of the band for a beam overlap with its frequency neighbours. Bfc is the maximum bandwidth allowed for any beam. With this overlap, the signal separation of —35 dB between the beams is maintained as the beams are pointing in different direction in space.
Image
The figure shows the default mode of a 7 beam fan, covering 70 to 120 kHz, using the shortest available pulse duration of 448 us. The vertical bars show the bandwidth of each beam. In linear mode they are allowed to slightly overlap.
Linear mode with I-shape
In this special case where we use the Beam Spacing Alternative parameter equal linear and the Beam Spacing Linear parameter is set to 0 degrees (I-shape), no overlap frequency is allowed as all beams point in the same direction. Separation in this case is set to 1.0.
Image
The figure shows the default mode of a 7 beam fan, covering 70 to 120 kHz, but in this case with the I-shape beam shaping. With no separation in space, the maximum allowable bandwidth for each beam is less and the shortest allowable pulse duration is now 512 us.The vertical bars show the bandwidth of each beam. In this case they do not overlap.
Linear mode with reference beam frequency control
Reference beams located outside of the selected frequency band may be allocated any frequency between the frequency limits and the selected band. Be aware that this allows for reference beams close in frequency to the beams in the fan, inside the frequency band. It is possible to set less frequency separation in this ase than the system would use if the reference beams was located inside of the selected band width.
This may result in signal leakage between beam and the fan and reference beams. Use the Frequency Plot page to observe the resulting frequency distribution.
Image
The figure shows the default mode of a 7 beam fan, modified to cover 71–119 kHz, using the shortest allowable pulse duration, for this reduced band, of 512 us.
Two reference beams have been added at 70 and 120 kHz respectively.
Again, the vertical bars show the bandwidth of each beam. The beams in the fan are allowed to slightly overlap. The reference beams however, are configured in frequency next to the beams in the fan. As all beams have the same pulse duration, we have to been allowed to create a significant overlap in frequency between the reference beams and their frequency neighbour beams. Such a configuration will have a reduced signal separation capability.