U.S. patent application number 10/557768 was filed with the patent office on 2006-12-07 for selectable range lobes using wide-band array.
Invention is credited to Kent Olof Falk.
Application Number | 20060273948 10/557768 |
Document ID | / |
Family ID | 33476139 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060273948 |
Kind Code |
A1 |
Falk; Kent Olof |
December 7, 2006 |
Selectable range lobes using wide-band array
Abstract
The present inventive concept for bistatic or monostatic radar
utilization discloses a method and a system for unambiguous range
resolution utilizing an ultra wide-band signal, generally a
wide-band noise signal which may be continuous bandwidth limited
white or colored noise. The noise signal is typically generated and
radiated by a transmitting antenna covering the entire reception
range of a receiving sparse antenna. An echo signal is received by
the receiving antenna. By means of a selected auto-correlation
function defining the wide-band noise signal power spectrum, the
convolution of the radiated output signal and the received echo
input signal will give the target range information.
Inventors: |
Falk; Kent Olof; (Goteborg,
SE) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
33476139 |
Appl. No.: |
10/557768 |
Filed: |
October 20, 2003 |
PCT Filed: |
October 20, 2003 |
PCT NO: |
PCT/SE03/01616 |
371 Date: |
December 19, 2005 |
Current U.S.
Class: |
342/89 ; 342/159;
342/189; 342/196; 342/85 |
Current CPC
Class: |
G01S 2013/0281 20130101;
H01Q 21/08 20130101; G01S 7/2813 20130101; G01S 13/0209 20130101;
H01Q 21/28 20130101; H01Q 21/205 20130101 |
Class at
Publication: |
342/089 ;
342/196; 342/159; 342/189; 342/085 |
International
Class: |
G01S 13/00 20060101
G01S013/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2003 |
SE |
SE03/00833 |
Claims
1. A system for controlled range side-lobes in a bistatic or
monostatic radar system, characterized in that an ultra wide-band
band microwave signal is generated and radiated via a transmitter
antenna, echo signals are received via receiver antennas; whereby a
transmitted power spectrum of a transmitted signal and its
auto-correlation function form a Fourier transform pair, such that
for a given range sidelobe characteristic the power spectrum of a
corresponding output signal is calculated as an inverse Fourier
transform of given range sidelobe characteristic.
2. The system according to claim 1, characterized in that the ultra
wide-band microwave signal is generated as band-limited white
noise, the convolution result being read out as a signature of the
target for 100% bandwidth approximately in form of the derivative
of the target area as function of range.
3. The system according to claim 1, characterized in that the ultra
wide-band microwave signal is generated as band-limited colored
noise, by using a selected auto-correlation function for the
generated noise.
4. The system according to claim 1, characterized in that the ultra
wide-band microwave signal comprises a frequency range of the same
order as the center frequency.
5. The system according to claim 1, characterized in that the
antenna used are vertical linear arrays.
6. The system according to claim 1, characterized in that the
receiver antennas form a circular array.
7. The system according to claim 1, characterized in that in an
monostatic configuration an omnidirectional transmitting antenna is
generally positioned at another height than receiving antennas to
minimize leakage between transmit and receive antennas.
8. A method for obtaining controlled range side-lobes in a bistatic
or monostatic radar operation, characterized by the steps of
generating an ultra wide-band band microwave signal being radiated
via a transmitter antenna; arranging receiving microwave antennas;
forming a Fourier transform pair with a transmitted power spectrum
of transmitted signal and its auto-correlation function;
calculating for a given range sidelobe characteristic the power
spectrum of the corresponding output signal as the inverse Fourier
transform of the given range sidelobe characteristic.
9. The method according to claim 8, characterized by the further
steps of generating the ultra wide-band microwave signal as
band-limited white noise, and reading out the convolution result as
a signature of the target for 100% bandwidth approximately in form
of the derivative of the target area as function of range.
10. The method according to claim 8, characterized by the further
step of generating the ultra wide-band microwave signal as
band-limited colored noise by using a selected auto-correlation
function for the generated noise.
11. The method according to claim 8, characterized by the further
step of generating the ultra wide-band microwave signal in a
frequency range having an order about equal to the value of the
center frequency.
12. The method according to claim 8, characterized by the further
step of using vertical linear arrays as antennas.
13. The method according to claim 8, characterized by the further
step of using circular arrays as receiving antenna.
14. The method according to claim 8, characterized by the further
step of in a monostatic configuration generally positioning an
omnidirectional transmitting antenna at a different height compared
to the receiving antennas to minimize leakage between transmit and
receive antennas.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method and system for
unambiguous range resolution of a radar system.
BACKGROUND
[0002] In radar systems there is a desire to keep peak power as low
as possible to minimize the risk of detection.
[0003] Typical solutions of today utilize fully range coded long
pulses, for instance using a binary phase code. Signal
classification is difficult with present solutions and different
hardware solutions have to be used for a respective function
category, for instance, a radar function or a jamming function.
[0004] Therefore there is a demand for large duty cycle (low peak
power) good range estimation for wide-band system not necessarily
being pulse coded with non-deterministic transmit signals.
SUMMARY OF THE INVENTION
[0005] A method and a system for controlling range resolution of a
radar system in a bistatic or monostatic configuration utilize an
ultra-wide-band signal, which in a typical embodiment may be
continuous bandwidth limited white or colored noise. The noise
signal is generated and radiated for instance by an omnidirectional
transmitting antenna covering the entire reception range of a
receiving antenna and an echo signal is received by the receiving
antenna. By means of a selected auto-correlation function defining
the wide-band noise signal power spectrum, the convolution of the
radiated output signal and the received echo input signal the
target range information is obtained.
[0006] A system according to the present invention is set forth by
the independent claim 1, and further embodiments of the invention
are set forth by the dependent claims 2 to 9.
[0007] Further a method according to the present invention is set
forth by the independent claim 10, and further embodiments are
defined by the dependent claims 11 to 18.
SHORT DESCRIPTION OF THE DRAWINGS
[0008] The invention, together with further objects and advantages
thereof, may best be understood by referring to the following
detailed description taken together with the accompanying drawings,
in which:
[0009] FIG. 1 illustrates an illustrative array antenna for use
according to the present inventive concept;
[0010] FIG. 2 illustrates a principal embodiment of a wide-band
array used in line with the present inventive idea and having the
number of receiving antenna elements n=32;
[0011] FIG. 3 illustrates in a number of graphs a) to f) the
auto-correlation function for Gaussian noise with bandwidth from
200% and down to 6.25% expressed as percent of center
frequency;
[0012] FIG. 4 illustrates in a number of graphs a) to f) the
auto-correlation function for white bandwidth limited noise using a
bandwidth from 200% and down to 6.25% expressed as percent of
center frequency; and
[0013] FIG. 5 illustrates in a graph the convolution of radiated
and received signal as a function of signal-to-noise ratio.
DETAILED DESCRIPTION
[0014] In a typical illustrative embodiment a very broad-banded
signal is generated. The generated signal may be continuous
band-limited white or colored noise and transmitted by an antenna,
which for instance is isotropic in its horizontal plane. Echo
signals in a bistatic or monostatic configuration are received.
[0015] Each antenna may be a vertical array to increase the gain in
the horizontal plane. To minimize leakage between the transmitting
antenna and the receiver antennas the transmitting antenna
preferably is positioned as far as possible from the receiving
antennas and for instance at a different height.
[0016] FIG. 1 illustrates a principal shape with n=3, the
transmitting antenna is denoted as 1 and the receiver antennas are
denoted 3. A structure carrying the transmitter antenna is denoted
as reference number 5. A transmitter and n receivers with
accompanying signal processing is housed in the electronic unit 7.
FIG. 2 illustrates a practical embodiment of a circular array with
n=32, the transmitting antenna sitting elevated in the middle and
the receiving antenna in a ring below. One transmitter, n receivers
with accompanying signal processing being housed in the base of the
array.
[0017] The range to the target is determined by finding the peaks
in the convolution between the input and output signal.
Basic Theory
[0018] Suppose that the radar station is not moving and transmits
the ergodic waveform s(t) having a zero average value. For a
non-moving target having an extension L and a target area profile
.rho.(.tau.) the received signal r(t) may be written according to:
r .function. ( t ) = .intg. 2 ( R - L / 2 ) c 0 2 ( R + L / 2 ) c 0
.times. .rho. .function. ( .zeta. ) s .function. ( t - .zeta. )
.times. d .zeta. + n .function. ( t ) ( 1 ) ##EQU1## where R is the
target range, .zeta. the time integration variable and c.sub.0 the
velocity of light. n(t) represents additive noise and possible
disturbances.
[0019] According to the theory for ergotic processes also r(t)
becomes stationary and ergotic. Therefore the time correlation may
be used for approximating the cross-correlation between a delayed
copy of the conjugate of the transmit signal s*(t-c) and the
received signal r(t) according to: g T .function. ( t , .tau. ) =
.intg. - T / 2 T / 2 .times. .intg. 2 ( R - L / 2 ) c 0 2 ( R + L /
2 ) c 0 .times. .times. .rho. .function. ( .zeta. ) s .function. (
t - .zeta. ) s * .function. ( t - .tau. ) d .zeta. d t + .intg. - T
/ 2 T / 2 .times. n .function. ( t ) s * .function. ( t - .tau. ) d
t ( 2 ) ##EQU2## where T represents the correlation integration
interval. For large T:s the second term of equation (2) will go
towards zero as n(t) is not correlated with the transmit signal
s(t). This gives: g .function. ( .tau. ) = lim T -> .infin.
.times. g T .function. ( t ) = .intg. 2 ( R - L / 2 ) c 0 2 ( R + L
/ 2 ) c 0 .times. .rho. .function. ( .zeta. ) p .function. ( .tau.
- .zeta. ) d .zeta. = .rho. .function. ( .tau. ) p .function. (
.tau. ) ( 3 ) ##EQU3## {circle around (.times.)} symbolizes
convolution. Besides it is valid that: p .function. ( .tau. ) = lim
T -> .infin. .times. .intg. - T / 2 T / 2 .times. s .function. (
t ) s * .function. ( t - .tau. ) d t ( 4 ) ##EQU4## where
.rho.(.tau.) is the auto-correlation function of the transmitted
noise signal s(t).
[0020] It comes out of equation (3) that the received signal is the
convolution of the target area profile and the auto-correlation
function of the transmitted signal. Thus the range resolution of
the auto-correlation function .tau.(.tau.) of the transmit signal
depends on the bandwidth of the transmit signal and the form of its
power spectrum P(.omega.). It is easy to prove that there is a
simple relation between the auto-correlation function .rho.(.tau.)
of the signal and it power spectrum P(.omega.). These constitute
namely a pair of Fourier transforms: P .function. ( .omega. ) =
.intg. - .infin. .infin. .times. p .function. ( t ) e - j .omega.
.tau. .times. d .tau. p .function. ( .tau. ) = 1 2 .pi. .intg. -
.infin. .infin. .times. P .function. ( .omega. ) e j .omega. .tau.
.times. d .omega. } ( 5 ) ##EQU5##
[0021] Thus, it is possible to select range resolution .rho.(.tau.)
and calculate power spectrum P(.OMEGA.).
[0022] Examples of Auto-Correlation Functions
[0023] In FIGS. 2 and 3 the auto-correlation function is
demonstrated as a function of time t. But time is directly
proportional to the range R according to equation (6) t = 2 R c 0 (
6 ) ##EQU6## for Gaussian noise the auto-function may be written
as: p .function. ( .tau. ) = .sigma. 2 cos .function. [ ( .omega. 2
+ .omega. 1 ) .tau. 2 ] e - ( .omega. 2 - .omega. 1 ) .tau. 2 ( 7 )
##EQU7##
[0024] For white bandwidth limited noise the auto-correlation
function may be written as: p .function. ( .tau. ) = .sigma. 2 cos
.function. [ ( .omega. 2 + .omega. 1 ) .tau. 2 ] sin .function. [ (
.omega. 2 - .omega. 1 ) .tau. 2 ] ( .omega. 2 - .omega. 1 ) .tau. 2
( 8 ) ##EQU8## where like in Equation (7) .sigma. denotes the noise
standard deviation and the mean power of the noise signal is
.sigma..sup.2 and .omega..sub.1 and .omega..sub.2 are the lower and
upper limits of the angular velocity. Simulations
[0025] FIG. 4 demonstrates the auto-correlation function for white
bandwidth limited noise according to equation (1). As can be seen a
bandwidth of 100% is needed to get the sidelobes down to a
reasonable level.
[0026] For the simulations 100% bandwidth and a center frequency of
12 GHz was chosen. In other words the frequency range of the radar
was 6-18 GHz. The distance to the target is determined by finding
the peaks of the convolution between input and output signal.
[0027] FIG. 5 illustrates a simulation result when signal-to-noise
was varied. In this case the target is an object, 1 meter long,
standing still at a distance of 750 meters. The target area as
function of distance is an equally distributed random number per
distance sample. The sampling rate in this case was 50 GHz. From
the response of the convolution the signature of the target can be
interpreted in the form of the derivative of target area as
function of distance. This may then be used to classify and
identify the target by comparison with suitable library data.
[0028] Interesting is that the auto-correlation function as a
matter of fact can be chosen such that desired characteristics are
obtained. The Fourier transform of the selected auto-correlation
function gives necessary power spectrum of the radiated signal.
[0029] It will be understood by those skilled in the art that
various modifications and changes could be made to the present
invention without departure from the spirit and scope thereof,
which is defined by the appended claims.
* * * * *