Gated continuous wave radar

1. A method for operating a stepped frequency continuous wave (SFCW) ground penetrating radar (GPR), the method comprising:

transmitting, by a transmitter, a first set of continuous wave (CW) signals, each CW signal of the first set of CW signals having a first signal frequency, and the transmitter being turned off between transmission of each CW signal of the first set of CW signals;

for each CW signal of the first set of CW signals:

receiving a reflection of the CW signal, and

selecting an analog to digital (A/D) sample of the reflection of the CW signal that does not contain ground reflections by selecting the A/D sample based on timing from the transmitter being turned off after transmission of the CW signal; and

integrating the selected A/D samples from each of the CW signals of the of the first set of CW signals to obtain a single A/D sample for the first set of CW signals.

2. The method of claim 1 , further comprising:

transmitting, by the transmitter, a second set of CW signals, each CW radar signal of the second set of CW signals having a second signal frequency different from the first signal frequency, and the transmitter being turned off between transition of each CW signal of the second set of CW signals;

for each CW signal of the second set of CW signals:

receiving a reflection of the CW signal, and

selecting an analog to digital (A/D) sample of the reflection of the CW signal that does not contain ground reflections by selecting the A/D sample based on timing from the transmitter being turned off after transmission of the CW signal; and

integrating the selected A/D samples from each of the CW signals of the of the second set of CW signals to obtain a single A/D sample for the second set of CW signals.

3. The method of claim 1 , wherein the CW signals in the first set of CW signals are transmitted and corresponding reflections are sampled in a series of gating cycles of a first frequency window.

4. The method of claim 1 , wherein sample timing for the selecting the A/D sample of the reflection of the CW signal comprises shifting a phase of a clock signal for an A/D converter to permit sub-sample timing resolution.

5. The method of claim 1 , wherein the timing is based on a time delay.

6. The method of claim 5 , wherein the time delay is based on estimating a distance of a GPR head from a ground.

7. The method of claim 5 , wherein the time delay is determined by:

receiving an un-gated return signal;

identifying a ground reflection within the un-gated return signal; and

adjusting the time delay based on the identified ground reflection.

8. The method of claim 1 , wherein a sample rate of the A/D samples is one giga-samples per second (1 Gsps).

9. The method of claim 1 , further comprising for each CW signal of the first set of CW signals, switching a receiver off during transmission of the CW signal.

10. A method for gating continuous wave (CW) signals of a stepped frequency continuous wave (SFCW) ground penetrating radar (GPR), the method comprising:

obtaining a first set of analog to digital (A/D) samples of a transmitted CW signal;

obtaining a second set of A/D samples of reflections of the transmitted CW signal;

determining, based on the first set of A/D samples, a time that transmission of the transmitted CW signal stops; and

selecting, based on the time that transmission of the transmitted CW signal stops and a delay period, an A/D sample from the second set of A/D samples that does not contain ground reflections of the transmitted CW signal.

11. The method of claim 10 , further comprising:

determining, based on the first set of A/D samples, a second time that transmission of the transmitted CW signal stops;

selecting, based on the second time that the transmission of the CW signal stops and the delay period, a second A/D sample from the second set of A/D samples that does not contain ground reflections of the transmitted CW signal; and

integrating the A/D sample and the second A/D sample.

12. The method of claim 10 , wherein the delay period is based on a distance of a GPR head from a ground.

13. The method of claim 10 , wherein the A/D samples are obtained from a pipeline A/D converter.

14. The method of claim 10 , wherein a sample rate of the A/D samples is one giga-sample per second (1 Gsps).

15. The method of claim 10 , wherein the delay period is based on estimating a distance of a GPR head from a ground.

16. A ground penetrating radar (GPR) device comprising:

an antenna configured to transmit and receive stepped frequency continuous wave (CW) radar signals;

a pipeline analog to digital (A/D) converter; and

an electronic processor coupled to an electronic storage, the electronic storage comprising instructions, that when executed, cause the processor to perform operations comprising:

transmitting, by a transmitter, a first set of continuous wave (CW) radar signals, each CW radar signal of the first set of CW radar signals having a first signal frequency, and the transmitter being turned off between transition of each CW radar signal of the first set of CW radar signals;

for each CW radar signal of the first set of CW radar signals:

receiving a reflection of the CW radar signal, and

selecting an analog to digital (A/D) sample of the reflection of the CW radar signal that does not contain ground reflections by selecting the A/D sample based on timing from the transmitter being turned off after transmission of the CW radar signal; and

integrating the selected A/D samples from each of the CW radar signals of the of the first set of CW radar signals to obtain a single A/D sample for the first set of CW radar signals.

17. The device of claim 16 , wherein the operations further comprise:

transmitting, by the transmitter, a second set of CW signals, each CW radar signal of the second set of CW signals having a second signal frequency different from the first signal frequency, and the transmitter being turned off between transition of each CW signal of the second set of CW signals;

for each CW signal of the second set of CW signals:

receiving a reflection of the CW signal, and

selecting an analog to digital (A/D) sample of the reflection of the CW signal that does not contain ground reflections by selecting the A/D sample based on timing from the transmitter being turned off after transmission of the CW signal; and

integrating the selected A/D samples from each of the CW signals of the of the second set of CW signals to obtain a single A/D sample for the second set of CW signals.

18. The device of claim 16 , wherein the CW signals in the first set of CW signals are transmitted and corresponding reflections are sampled in a series of gating cycles of a first frequency window.

19. The device of claim 16 , wherein sample timing for the selecting the A/D sample of the reflection of the CW signal comprises shifting a phase of a clock signal for an A/D converter to permit sub-sample timing resolution.

20. The device of claim 16 , wherein the timing is based on estimating a distance of a GPR head from a ground.