Amplitude envelope correction

Patent metadata

Field	Value
Publication number	US-10001548-B2
Application number	US-201514718064-A
Country	US
Kind code	B2
Filing date	May 20, 2015
Priority date	Jan 23, 2015
Publication date	Jun 19, 2018
Grant date	Jun 19, 2018

Abstract

A system that has a chirp generator for emitting signals and an amplitude modulator for shaping the signals emitted by the chirp generator. The signals are shaped using a calibration ramp. The system further includes a Radio Frequency (RF) power amplifier for amplifying the signals shaped by the amplitude modulator, an RF power detector for measuring power levels of the signals amplified by the RF power amplifier, and a pre-distortion coefficient generator for adjusting the measured power levels using power detector calibration coefficients that correspond to the RF power detector.

First claim

What is claimed is:

1. A method for producing one or more radar signals, the method comprising:
generating at least one first signal using a chirp generator, wherein the at least one first signal includes a full amplitude square pulse;
shaping the at least one first signal using an amplitude modulator by applying, via a digital-to-analog converter, a calibration ramp, wherein the calibration ramp has a duration of less than a duration of the square pulse and is sufficient to cover the full control range of the amplitude modulator;
detecting a power output level of the at least one first signal;
generating a capture ramp corresponding to the at least one first signal by applying an analog-to-digital converter to the detected power output level of the at least one first signal;
applying one or more power detector calibration coefficients to the capture ramp to form an adjusted capture ramp corresponding to the at least one first signal, wherein the power detector calibration coefficients are generated during a calibration process and used to adjust the detected power output level of the at least one first signal;
generating one or more pre-distortion coefficients by comparing the calibration ramp to the adjusted capture ramp;
applying the one or more pre-distortion coefficients to one or more envelope shape coefficients to form one or more adjusted envelope shape coefficients;
generating at least one second signal using the chirp generator;
shaping the at least one second signal using the amplitude modulator by applying, via the digital-to-analog converter, the one or more adjusted envelope shape coefficients to shape the at least one second signal to pre-distort the at least one second signal to account for distortion produced by a transmitter amplitude module; and
producing one or more radar signals from an antenna using the shaped at least one second signal.

2. The method of claim 1 , wherein the power detector calibration coefficients are generated by comparing power level measurements of a Radio Frequency (RF) power detector and a calibrated power meter.

3. The method of claim 1 , wherein the capture ramp is measured by a Radio Frequency (RF) power detector.

4. The method of claim 3 , wherein the power detector calibration coefficients correspond to the RF power detector.

5. The method of claim 1 , wherein applying power detector calibration coefficients to the capture ramp comprises using a calibration table to modify the capture ramp.

6. The method of claim 1 , wherein applying the one or more pre-distortion coefficients to one or more envelope shape coefficients comprises:
subtracting the one or more pre-distortion coefficients from the envelope shape coefficients.

7. The method of claim 1 , wherein the power detector calibration coefficients are selected from a plurality of power detector calibration coefficients and the selection is based at least in part on a measured temperature.

8. The method of claim 1 , wherein the calibration ramp is a linear function or a chirp envelope shape including ramp up and ramp down directions.

9. The method of claim 1 , wherein the power detector calibration coefficients are generated at a factory or production facility and the pre-distortion coefficients are generated on a marine vessel.

10. A system for producing one or more radar signals, the system comprising:
a chirp generator configured to emit signals, wherein the chirp generator is configured to emit at least one first signal that includes a full amplitude square pulse, wherein the chirp generator is configured to emit at least one second signal;
an amplitude modulator configured to shape the emitted signals from the chirp generator, wherein the amplitude modulator is configured to shape the at least one first signal by applying, via a digital-to-analog converter, a calibration ramp, wherein the calibration ramp has a duration of less than a duration of the square pulse and is sufficient to cover the full control range of the amplitude modulator;
a Radio Frequency (RF) power amplifier configured to amplify the signals shaped by the amplitude modulator;
an RF power detector configured to detect a power output level of the at least one first signal;
a capture ramp generator configured to generate a capture ramp corresponding to the at least one first signal by applying an analog-to-digital converter to the detected power output level of the at least one first signal;
a pre-distortion coefficient generator configured to apply one or more power detector calibration coefficients to the capture ramp to form an adjusted capture ramp corresponding to the at least one first signal, wherein the power detector calibration coefficients are generated during a calibration process and used to adjust the detected power output level of the at least one first signal, wherein the pre-distortion coefficient generator is configured to generate one or more pre-distortion coefficients by comparing the calibration ramp to the adjusted capture ramp;
wherein the amplitude modulator is configured to shape the at least one second signal by applying, via the digital-to-analog converter, one or more adjusted envelope shape coefficients to shape the at least one second signal to pre-distort the at least one second signal to account for distortion produced by a transmitter amplitude module, wherein the one or more adjusted envelope shape coefficients are formed based on application of the one or more pre-distortion coefficients to one or more envelope shape coefficients; and
an antenna configured to produce one or more radar signals using the shaped at least one second signal.

11. The system of claim 10 , wherein the pre-distortion coefficients and power detector calibration coefficients are configured to reduce power input to power output non-linearity in the system.

12. The system of claim 10 , wherein the amplitude modulator is configured to receive input from the digital-to-analog converter (DAC), wherein the RF power amplifier is connected to an RF forward power coupler, and wherein the RF forward power coupler is connected to the RF power detector.

13. The system of claim 12 , wherein the calibration ramp is an input to the DAC.

14. The system of claim 10 , wherein the power detector calibration coefficients are determined from a calibration table.

15. The system of claim 10 , wherein at least one of the amplitude modulator, the chirp generator, and the pre-distortion coefficient generator is implemented in one or more Field Programmable Gate Arrays.

Assignees

• Navico Holding As

Inventors

• Phillips Roger
• Storz Gregor
• Lilburn Lindsay

Classifications

• G01S7/282

  Transmitters · CPC title

• G01S7/2921

  based on data belonging to one radar period · CPC title

• G01S13/956

  mounted on ship or other platform · CPC title

• G01S13/28

  with time compression of received pulses · CPC title

• G01S13/937

  of marine craft · CPC title