Noise cancellation method and apparatus

A method for transmitting radio frequency energy in response to a trigger signal, comprising the steps of:

• feeding a radio frequency signal to an amplifier, such amplifier being operated at an initial operating point;
• successively changing the operating point of the amplifier in response to the trigger signal to drive the amplifier towards saturation;
• monitoring a ratio of amplifier input power to output power as the amplifier is being driven towards saturation;
• terminating said drive when the monitored ratio indicates the amplifier is operating at, or near saturation.

A method for operating a traveling wave tube, comprising the steps of:

• (a) operating the amplifier at a first operating point;
• (b) measuring input power to the amplifier and output power from the amplifier at the first operating point;
• (c) increasing power in a signal fed to the amplifier to drive the amplifier towards saturation to a second operating point;
• (d) measuring input power to the amplifier and output power from the amplifier at the output power at the second operating point;
• (e) determining a gain slope ratio representative of the difference between measured output powers to measured input powers;
• (f) comparing the determined gain slope ratio to a predetermined reference value representative of a point at a predetermined level below amplifier saturation;
• (g) repeating steps (c) through (f) until the determined gain slope ratio is less than the predetermined reference value;
• (h) when the predetermined gain slope reaches a level less than the predetermined reference value, calculating a ratio of a pair of successive changes in the gain slope ratio to changes in input power level associated with such pair of successive gain slope changes;
• (i) calculate a drive level required to enable the amplifier to reach the predetermine value representative of the operating point at a predetermined level less than amplifier saturation;
• (j) setting the operating point of the amplifier to a point a predetermined level above and below the drive level calculated in step (i);
• (k) measuring the amplifier input power and output power at the drive level setting in step (j);
• (l) calculating the gain slope from the input power and output power measured in step (k);
• (m) comparing the gain slope calculated in step (l) to the predetermined value;
• (n) repeating steps (i) through (m) until the gain slope calculated in step (l) substantially reaches the predetermined value;
• and then
• (o) setting the amplifier drive level to the gain slope calculated in step (l).

A method for canceling phase modulated noise in a phase modulation cancellation system having a phase detector fed by a portion of an input signal, an electronically controllable phase modulator fed by another portion of the input signal as a first input signal to the electronically controllable phase modulator, and a feedback phase shifter fed by an output from the phase cancellation system for changing the phase shift of the signal fed thereto in accordance with a control signal, such phase shifted signal being fed as a second input signal to the electronically controllable phase modulator, comprising the steps of:

• (a) during a calibration mode:
• (i) setting an initial value for the feedback phase shifter with the control signal;
• (ii) sequentially changing phase shift with the control signal while measuring a voltage produced by the phase detector to control the phase shift provided by the electronically controllable phase modulator to the signal fed thereto;
• (iii) determining when the voltage produced by the phase detector passes through a predetermined level with a predetermined slope polarity;
• and
• (b) during a subsequent normal operating mode, setting the phase detector to such value as a nominal operating point.

A radar transmitter, comprising;

• a radio frequency local oscillator for producing a radio frequency signal;
• a phase modulator fed by a portion of the radio frequency signal;
• a phase detector fed by a portion of the radio frequency signal, such phase detector producing an output to control the phase modulator;
• an first electronically controlled variable attenuator fed by the phase modulator;
• an amplifier fed the attenuator;
• a differencing amplifier fed by a portion of a signal produced by the amplifier and a reference voltage;
• a second electronically controllable variable attenuator fed by a portion of the signal produced by the amplifier;
• a travelling wave tube amplifier, fed by the second electronically controllable variable attenuator;
• a detector fed by a portion of the signal produced by the amplifier;
• an electronically controllable phase shifter fed by a portion of the signal produced by the amplifier, such phase shifter feeding the phase detector;
• a microcontroller;
• a first switch controllable by the microcontroller for selectively coupling the output of the detector to the microcontroller during an amplitude modulation calibration mode, such microcontroller producing the reference level for a subsequent phase modulation noise calibration mode and a then subsequent normal operating mode, such first switch decoupling the detector from the microcontroller during the phase modulation mode and the normal operating mode;
• a second switch fed by the phase detector controllable by the microcontroller for coupling the phase detector to the microcontroller during a phase modulation calibration mode, such microcontroller adjusting the electronically controllable phase shifter during the phase modulation noise calibration mode to produce a nominal operating point of operation for the phase detector during a subsequent normal operating mode and for decoupling the phase detector from the microcontroller during the amplitude modulation noise calibration mode and the normal operating mode;
• a pair of switches controllable by the microcontroller for coupling the phase detector to the electronically adjustable phase modulator and the detector to the second electronically controllable attenuator during the normal operating mode and for decoupling the phase detector from the electronically adjustable phase modulator and the detector from the second electronically controllable attenuator during the amplitude modulation noise calibration phase and the phase modulation noise calibration mode.

A method for operating an amplifier, comprising the steps of:

• feeding a signal to the amplifier, such amplifier being operated at an initial operating point;
• successively changing the operating point of the amplifier in response to the trigger signal to drive the amplifier towards saturation;
• monitoring a ratio of amplifier input power to output power as the amplifier is being driven towards saturation;
• terminating said drive when the monitored ratio indicates the amplifier is operating at, or near saturation.

A method for operating an amplifier, comprising the steps of:

• (a) operating the amplifier at a first operating point;
• (b) measuring input power to the amplifier and output power from the amplifier at the first operating point;
• (c) increasing power in a signal fed to the amplifier to drive the amplifier towards saturation to a second operating point;
• (d) measuring input power to the amplifier and output power from the amplifier at the output power at the second operating point;
• (e) determining a gain slope ratio representative of the difference between measured output powers to measured input powers;
• (f) comparing the determined gain slope ratio to a predetermined reference value representative of a point at a predetermined level below amplifier saturation;
• (g) repeating steps (c) through (f) until the determined gain slope ratio is less than the predetermined reference value;
• (h) when the predetermined gain slope reaches a level less than the predetermined reference value, calculating a ratio of a pair of successive changes in the gain slope ratio to changes in input power level associated with such pair of successive gain slope changes;
• (i) calculate a drive level required to enable the amplifier to reach the predetermine value representative of the operating point at a predetermined level less than amplifier saturation;
• (j) setting the operating point of the amplifier to a point a predetermined level above and below the drive level calculated in step (i);
• (k) measuring the amplifier input power and output power at the drive level setting in step (j);
• (l) calculating the gain slope from the input power and output power measured in step (k);
• (m) comparing the gain slope calculated in step (l) to the predetermined value;
• (n) repeating steps (i) through (m) until the gain slope calculated in step (l) substantially reaches the predetermined value;
• and then
• (o) setting the amplifier drive level to the gain slope calculated in step (l).

A method for operating a phase modulation cancellation system having a phase detector fed by a portion of an input signal, an electronically controllable phase modulator fed by another portion of the input signal as a first input signal to the electronically controllable phase modulator, and a feedback phase shifter fed by an output from the phase cancellation system for changing the phase shift of the signal fed thereto in accordance with a control signal, such phase shifted signal being fed as a second input signal to the electronically controllable phase modulator, comprising the steps of:

• (a) during a calibration mode:
• (i) setting an initial value for the feedback phase shifter with the control signal;
• (ii) sequentially changing phase shift with the control signal while measuring a voltage produced by the phase detector to control the phase shift provided by the electronically controllable phase modulator to the signal fed thereto;
• (iii) determining when the voltage produced by the phase detector passes through a predetermined level with a predetermined slope polarity;
• and
• (b) during a subsequent normal operating mode, setting the phase detector to such value as a nominal operating point.

A system, comprising;

• an oscillator for producing a signal;
• a phase modulator fed by a portion of the oscillator produced signal;
• a phase detector fed by a portion of the oscillator produced, such phase detector producing an output to control the phase modulator;
• an first electronically controlled variable attenuator fed by the phase modulator;
• an amplifier fed the attenuator;
• a differencing amplifier fed by a portion of a signal produced by the amplifier and a reference voltage;
• a second electronically controllable variable attenuator fed by a portion of the signal produced by the amplifier;
• an amplifier, fed by the second electronically controllable variable attenuator;
• a detector fed by a portion of the signal produced by the amplifier;
• an electronically controllable phase shifter fed by a portion of the signal produced by the amplifier, such phase shifter feeding the phase detector;
• a microcontroller;
• a first switch controllable by the microcontroller for selectively coupling the output of the detector to the microcontroller during an amplitude modulation calibration mode, such microcontroller producing the reference level for a subsequent phase modulation noise calibration mode and a then subsequent normal operating mode, such first switch decoupling the detector from the microcontroller during the phase modulation mode and the normal operating mode;
• a second switch fed by the phase detector controllable by the microcontroller for coupling the phase detector to the microcontroller during a phase modulation calibration mode, such microcontroller adjusting the electronically controllable phase shifter during the phase modulation noise calibration mode to produce a nominal operating point of operation for the phase detector during a subsequent normal operating mode and for decoupling the phase detector from the microcontroller during the amplitude modulation noise calibration mode and the normal operating mode;
• a pair of switches controllable by the microcontroller for coupling the phase detector to the electronically adjustable phase modulator and the detector to the second electronically controllable attenuator during the normal operating mode and for decoupling the phase detector from the electronically adjustable phase modulator and the detector from the second electronically controllable attenuator during the amplitude modulation noise calibration phase and the phase modulation noise calibration mode.