7p) Lecture 2 
Wo +3u, 
Wo +, 
Wo TRANSMIT 
Wo -W 
wy a | 
QUADRATIC 
| PHASE 
' NETWORK 
Wet 3W TECTOR 
RECEIVE s 1 OETECTO 
2 ELEMENT MULTIPLIER 
ARRAY 
TO DISPLAY 
Fig, 2.12. Multifrequency sector-scanning system. 
ducer channel. Since, in the channel from the other transducer, only a fixed 
delay is provided, it is clear that effective scanning of the beam has been obtained. 
The design of the delay network is based on the phase-frequency charac- 
teristic 
$=aw*+bot+c 
which can be obtained with reasonable accuracy bya low-pass filter section with 
an abnormally high value ( ~ 3) of the derivation parameter m. 
2.3.3. Double- Transducer FM System 
As a result of his studies of echo location by bats, Kay has proposed a sonar 
system which, in addition to giving a possible explanation of the bat's echo- 
location acuity, indicates a line of development for man-made sonars which may 
be very profitable [18,19]. 
Suppose that the sector of search is insonified by a frequency-swept (or FM) 
continuous (or quasi-continuous) tone, and that two spaced transducers are used 
as receivers. If each of the latter is connected to its own conventional FM sonar 
receiver, then at the output of each receiver the range of any particular target 
is indicated by the frequency of the output echo signal. But if the target lies in 
a direction making an angle to the normal axis of the two transducers, the output 
frequencies will be different in the two receivers, since the ranges are different. 
