Radar methods and systems using ramp sequences
One embodiment of the present invention relates to a method for detecting a range and velocity of a target. In this method, an electromagnetic wave is transmitted over a frequency range, where a period of the wave comprises a number of consecutive ramps. A first ramp in the period is transmitted over a first portion of the frequency range, and a second ramp in the period is transmitted over a second portion of the frequency range that differs from the first portion. The second ramp is offset by a frequency shift relative to the first ramp. A scattered wave is received from the target and processed to determine the range and the velocity of the target. Other methods and systems are also disclosed.
1. A method for detecting a range and a velocity of a target, comprising:
transmitting an electromagnetic wave over a frequency range, wherein a period of the wave comprises a number of consecutive ramps, a first substantially triangular ramp in the period transmitted over a first portion of the frequency range, and a second substantially triangular ramp in the period transmitted over a second portion of the frequency range that differs from the first portion, the second substantially triangular ramp offset by a frequency shift relative to the first substantially triangular ramp;
receiving a scattered wave reflected from the target, where the scattered wave is generated when the transmitted electromagnetic wave reflects from the target; and
processing the received scattered wave to determine the range and the velocity of the target.
2. The method of claim 1 , wherein processing the scattered wave further comprises:
sampling values in the received scattered wave at approximately equally spaced sampling intervals; and
associating the sampled values with a frequency step.
3. The method of claim 2 , further comprising:
determining a range resolution for the target as a function of the number of consecutive ramps in the period and the frequency step.
4. The method of claim 2 , further comprising:
determining a velocity resolution for the target as a function of the number of consecutive ramps in the period and the ramp duration.
5. The method of claim 2 , further comprising
determining the range and the velocity of the target by performing a two-dimensional transform on the sampled values; and
applying a constant false alarm rate algorithm to a result of the two-dimensional transform to determine the range and the velocity of the target.
6. The method of claim 5 , wherein an estimated range of the target is given by the following relationship:
R
=
c
·
(
L
z
·
T
A
·
k
-
N
z
·
T
s
·
p
)
2
Δ
f
·
T
A
-
2
·
f
step
·
T
s
)
N
z
·
L
z
c representing the speed of light;
L Z and N z representing a number of points in the two dimensional transform after zero padding;
T s representing the ramp duration of the first and second ramp;
k and p representing locations of peaks in the two-dimensional transform
ΔF representing the frequency shift;
T A representing the sampling interval; and
f step representing the frequency step.
7. A method for detecting a range and a velocity of a target, comprising:
transmitting a first consecutive ramp over a first portion of a frequency range, the first consecutive ramp comprising a first ramp segment that is piece-wise continuous with a second ramp segment, wherein the first ramp segment has one of a positive and a negative slope and the second ramp segment has the other of the positive and the negative slope; and
transmitting a second consecutive ramp over a second portion of the frequency range that differs from the first portion of the frequency range, the second consecutive ramp comprising: a third ramp segment having approximately the one slope and being piece-wise continuous with the second ramp segment, and a fourth ramp segment having approximately the other slope and being piece-wise continuous with the third ramp segment.
8. The method of claim 7 , further comprising:
transmitting additional ramps over additional fractions of the frequency range, each additional ramp offset by the frequency shift relative to the ramps adjacent thereto.
9. The method of claim 7 , further comprising:
receiving a scattered wave reflected from the target, where the scattered wave is generated when the transmitted ramps reflect from the target;
sampling values in the received scattered wave at approximately equally spaced sampling intervals; and
associating the sampled values with a respective frequency step.
10. The method of claim 9 , further comprising:
determining a range resolution for the target as a function of both a number of consecutive ramps in a period of an electromagnetic wave associated with the transmitted ramps and the frequency step.
11. The method of claim 9 , further comprising:
determining a velocity resolution for the target as a function of both a number of consecutive ramps in a period of an electromagnetic wave associated with the transmitted ramps and a ramp duration associated with the transmitted ramps.
12. The method of claim 9 , further comprising
determining the range and the velocity of the target by performing a two-dimensional transform function on the sampled values; and
applying a constant false alarm rate algorithm to a result of the two-dimensional transform to determine the range and the velocity of the target.
13. A radar system, comprising:
a radar transmitter configured to transmit an electromagnetic wave over a frequency range, the electromagnetic wave including a first substantially triangular ramp associated with a first portion of the frequency range and a second substantially triangular ramp associated with a second portion of the frequency range that differs from the first portion, where the first substantially triangular ramp is offset by a frequency shift relative to the first substantially triangular ramp; and
a radar receiver configured to receive a scattered wave reflected from a target, and further configured to determine a range and a velocity of the target as a function of a two-dimensional transform performed on a baseband signal derived from the received scattered wave.
14. The radar system of claim 13 , wherein the radar transmitter comprises an analog circuit that comprises:
a voltage controlled oscillator configured to output a series of consecutive ramps to be transmitted over an antenna, and further configured to output a local oscillator frequency that down-converts the scattered wave to the baseband signal.
15. A radar system, comprising:
a memory configured to store ramp-shaping information about a series of consecutive ramps to be transmitted;
a control state machine configured to read the memory and present slope information related to the ramp shaping information to an accumulator; and
calibration and interpolation circuitry configured to receive un-interpolated frequency information from the accumulator and provide an interpolated value to an analog circuit that includes a voltage controlled oscillator.
16. The radar system of claim 15 , wherein the voltage controlled oscillator is configured to output a series of consecutive ramps to be transmitted over a transmit antenna based on the ramp shaping-information.
17. The radar system of claim 16 , where the voltage controlled oscillator is configured to output a local oscillator signal, the radar system further comprising:
a receive antenna for receiving a scattered wave that reflects from a target, where the scattered wave is generated when the transmitted radio wave reflects from the target;
a mixer for down-converting the scattered wave to a down-converted signal as a function of the local oscillator signal.
18. The radar system of claim 16 , wherein the series of consecutive ramps comprises:
a first consecutive ramp transmitted over a first portion of a frequency range, the first consecutive ramp comprising: a first ramp segment that is piece-wise continuous with a second ramp segment, wherein the first ramp segment has one of a positive and a negative slope and the second ramp segment has the other of the positive and the negative slope; and
a second consecutive ramp transmitted over a second portion of the frequency range that differs from the first portion, the second consecutive ramp comprising: a third ramp segment having approximately the one slope and being piece-wise continuous with the second ramp segment, and a fourth ramp segment having approximately the other slope and being piece-wise continuous with the third ramp segment.
19. A radar system, comprising:
a radar transmitter configured to transmit an electromagnetic wave over a frequency range, the electromagnetic wave including a first substantially triangular ramp associated with a first portion of the frequency range and a second substantially triangular ramp associated with a second portion of the frequency range that differs from the first portion, where the first substantially triangular ramp is offset by a frequency shift relative to the first substantially triangular ramp;
wherein the radar transmitter comprises an interpolation control circuit that works in conjunction with a calibration memory tuning law circuit to deliver a linear ramp segment within the first and second ramps.
20. A radar system, comprising:
a radar transmitter configured to transmit an electromagnetic wave over a frequency range, the electromagnetic wave including a first substantially triangular ramp associated with a first portion of the frequency range and a second substantially triangular ramp associated with a second portion of the frequency range that differs from the first portion, where the first substantially triangular ramp is offset by a frequency shift relative to the first substantially triangular ramp;
wherein the radar transmitter comprises:
a memory configured to store ramp-shaping information about the first and second ramps;
a control state machine configured to read ramp-shaping information from the memory and present slope information related to the ramp-shaping information to an accumulator; and
calibration and interpolation circuitry configured to receive un-interpolated frequency information from the accumulator and provide an interpolated value to a voltage controlled oscillator.