| 摘要 |
<p>The sonar antenna (1) comprises a vertical cylinder on which are placed a number of vertical columns of piezoelectric transducers. Each column is independently excited and a transmission channel is formed from a number of adjacent columns utilising phase shift circuits (T) to obtain the required directivity lobe. The lobe is shifted electronically to sweep the horizon. The acoustic transmission signals for two separate frequency bands (F1,F2) are provided by two generators (4,5). A changeover switch (6,7) operated by a control circuit (7) ensures the respective output is applied via a monostable gate (8) to obtain a particular pulse duration (theta). These pulses pass via the phase shift circuits (r) to a multiplexer (9) controlled by a sequencer (10) and then to the transmission circuits (11). Filters in the receiver preserve the energy reflected from a target and attenuate the reverberation frequencies.</p> |
