40 Lecture 2 
N/a SECTIONS N/> SECTIONS 
TRANSDUCER 
INT SECTIONS 
SWEPT 
PHASE SHIFTER WITH 
| LINEAR PHASE - SHIF T/ 
AMPLIFIERS FREQUENCY RESPONSE 
IF NEEDED 
LOW -PASS 
FILTER 
TO DISPLAY 
Fig. 2.10. Block schematic diagram of scanning sonar system with multiplicative operation. 
two 18-in.-diameter air-filled steel spheres were suspended in the water, and 
one was carefully moved relative to the other. When on exactly the same range, 
they were moved together slowly while photographs of the B-scan display were 
taken, This was done for both ordinary additive and for multiplicative operation. 
The figure shows the sphere echoes just clearly resolved in each case, and it is 
quite obvious that the multiplicative system not only has half the beamwidth, but 
twice the angular resolution as well. The effect of the reduced secondary re- 
sponses of the multiplicative system is also shown clearly in Fig. 2.11, where 
the receiving gain was greatly increased. With the additive system, the beam 
and its secondaries have spread right across the screen, due to the high intensity 
of the signal relative to the display threshold, but with the multiplicative system 
an interpretable display is still obtained. 
2.3.2. Within-Pulse Scanning Systems Using Multifrequency Arrays 
In the search for both better and cheaper scanning sonar systems, it is clear 
that the multifrequency two-element array (discussed in Section 2.2:3) has a 
potential attraction since it permits beam scanning to be done with a single 
variable time delay in one channel, in place of the complex series of phase 
shifters needed for the multielement array. Various kinds of variable time- 
delay networks are under consideration, but one which Welsby [10] has proposed 
for the narrow-band multifrequency system (mentioned at the end of Section 
2.2.3) is of particular interest. His system is shown in block form in Fig. 2.12, 
