Wideband sonar with pulse compression
A sonar transmitter includes digital logic that controls switches coupled to a primary coil of a transformer. The switches are driven to produce at least one voltage pulse across a secondary coil for the transformer to produce a series of voltage pulses approximating the desired signal. The transformer may comprise: a secondary coil having a plurality of windings arranged into a first section, a middle section, and a final section; and a primary coil winding wound only with the secondary coil windings forming the middle section.
1. A wideband sonar transmitter, comprising:
a power supply;
a pair of switches; and
a wideband transformer having a secondary coil for driving a transducer and a primary coil having a center tap driven by the power supply, wherein a first end of the primary coil couples to ground through a first one of the switches and a second end of the primary coil couples to ground through a second one of the switches, and wherein the wideband transformer includes a secondary coil including a plurality of windings arranged into a first section, a middle section, and a final section, and a primary coil winding wound only with the secondary coil windings forming the middle section.
2. The wideband sonar transmitter of claim 1 , wherein the switches comprise MOSFET transistors.
3. The wideband sonar transmitter of claim 1 , further comprising digital logic configured to generate on and off times for each of the switches in the pair of switches to approximate a desired waveform across the transducer.
4. The wideband sonar transmitter of claim 3 , wherein the digital logic includes an FPGA adapted to store an array of the on and off times.
5. The wideband transmitter of claim 4 , further comprising a CPU configured to select for a desired chirp waveform and to calculate the on and off times accordingly.
6. The wideband transformer of claim 1 , wherein the primary coil comprises two windings separated by a first center tap, and wherein the middle section of the secondary coil comprises two windings separated by a second center tap.
7. The wideband transformer of claim 1 , further comprising:
a first layer of insulation separating the first section from the middle section, and
a second layer of insulation separating the middle section from the final section.
8. The wideband transformer of claim 1 , wherein a leakage inductance for the primary coil winding is no greater than 1.0 μH over an operating frequency range of 25 KHz to 255 KHz.
9. The wideband transformer of claim 1 , wherein a shunt inductance for the primary coil winding is at least 2.2 mH over an operating range of 25 KHz to 255 KHz.
10. A method of generating wideband sonar pulses, comprising;
in digital logic, analyzing a desired wideband sonar signal to identify positive half cycles and negative half cycles of the desired signal; and
with regard to each half cycle, approximating the half cycle by driving switches coupled to a transformer's primary coil to produce at least one voltage pulse across a secondary coil for the transformer to produce a series of voltage pulses approximating the desired signal.
11. The method of claim 10 , wherein the switches are driven so as to pulse width modulate the voltage pulses so as to approximate a desired peak amplitude for each half cycle.
12. The method of claim 11 , wherein each half cycle is approximated by a single voltage pulse.
13. The method of claim 11 , wherein each half cycle is approximated by a pair of voltage pulses.
14. The method of claim 13 , wherein the switches are driven so as to produce a desired separation between the voltage pulses in each pair.
15. The method of claim 14 , wherein the desired separation suppresses a harmonic in an approximated signal formed by the series of voltage pulses.
16. A sonar, comprising
a power supply;
a pair of switches; and
a power amplifier including a wideband transformer having a secondary coil for driving a transducer and a center-tapped primary coil driven by the power supply, the center tap coupling to the pair of switches, wherein the wideband transformer includes:
a secondary coil including a plurality of windings arranged into a first section, a middle section, and a final section; and
a primary coil winding wound only with the secondary coil windings forming the middle section.
17. The sonar of claim 16 , further comprising a signal generator for driving the pair of switches so as to drive the secondary coil with an approximately sinusoidal voltage.
18. The sonar of claim 17 , wherein the power supply comprises a bank of capacitors controlled by the signal generator.
19. The sonar of claim 16 , wherein a leakage inductance for the primary coil winding is no greater than 1.0 μH over a sonar operating frequency range of 25 KHz to 255 KHz.