U.S. patent application number 12/525008 was filed with the patent office on 2010-02-04 for antenna system and radar system incorporating the same.
This patent application is currently assigned to QINETIQ LIMITED. Invention is credited to Christopher James Alder, Patrick David Lawrence Beasley, Graeme Neil Crisp, Michael Dean, Robert David Hodges, Barry John Hughes, Jeffrey Powell.
Application Number | 20100026563 12/525008 |
Document ID | / |
Family ID | 37891013 |
Filed Date | 2010-02-04 |
United States Patent
Application |
20100026563 |
Kind Code |
A1 |
Alder; Christopher James ;
et al. |
February 4, 2010 |
ANTENNA SYSTEM AND RADAR SYSTEM INCORPORATING THE SAME
Abstract
An antenna system comprising an array of antenna elements, the
array comprising a plurality of groups of antenna elements wherein
each group comprises one or more antenna elements arranged in
series, and wherein the system further comprises first
phase-control means for performing the function of introducing
respective phase-shifts to transmitted or received signals passed
to or received from each of said groups to provide beamforming and
second phase-control means for performing said function with
respect to a sub-set of said groups. An antenna system of the
invention allows two radar beam patterns having different spatial
characteristics to be generated using a single antenna system. The
invention also provides a radar system incorporating an antenna
system of the invention.
Inventors: |
Alder; Christopher James;
(Malvern, GB) ; Crisp; Graeme Neil; (Malvern,
GB) ; Hughes; Barry John; (Malvern, GB) ;
Beasley; Patrick David Lawrence; (Malvern, GB) ;
Powell; Jeffrey; (Malvern, GB) ; Dean; Michael;
(Malvern, GB) ; Hodges; Robert David; (Malvern,
GB) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
QINETIQ LIMITED
London
UK
|
Family ID: |
37891013 |
Appl. No.: |
12/525008 |
Filed: |
January 16, 2008 |
PCT Filed: |
January 16, 2008 |
PCT NO: |
PCT/GB08/00125 |
371 Date: |
July 29, 2009 |
Current U.S.
Class: |
342/200 ;
342/372 |
Current CPC
Class: |
G01S 7/352 20130101;
H01Q 25/008 20130101; G01S 7/023 20130101; H01Q 1/3233 20130101;
H01Q 21/065 20130101; H01Q 21/0031 20130101; H03B 23/00
20130101 |
Class at
Publication: |
342/200 ;
342/372 |
International
Class: |
G01S 13/00 20060101
G01S013/00; H01Q 3/00 20060101 H01Q003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2007 |
GB |
0701812.0 |
Claims
1. An antenna system comprising an array of antenna elements, the
array comprising a plurality of groups of antenna elements wherein
each group comprises one or more antenna elements arranged in
series, and wherein the system further comprises a first
phase-controller arranged to perform the function of applying
respective phase-shifts to transmitted or received signals passed
to or received from each of said groups to provide beamforming and
a second phase-controller for performing said function with respect
to a sub-set of said groups.
2. An antenna system according to claim 1 wherein at least one of
the first and second phase-controllers comprises a Rotman lens.
3. An antenna system according to claim 2 wherein both the first
and second phase-controllers each comprise a Rotman lens.
4. An antenna system according to claim 1 wherein the array of
antenna elements is substantially rectangular and each of said
groups of antenna elements is a row or column of the array.
5. An antenna system according to claim 4 wherein said sub-set of
groups is made up of contiguous rows or columns of the array.
6. An antenna system according to claim 5 wherein the array of
antenna elements is substantially planar.
7. An antenna system according to claim 4 wherein array of antenna
elements and the Rotman lenses are mounted on a common former.
8. An antenna system according to claim 7 wherein the former is
substantially cuboid and the first and second Rotman lenses are
mounted on respective opposite faces of the cuboid former and the
array of antenna elements is mounted on a face of the cuboid former
adjacent to the faces mounting the Rotman lenses.
9. An antenna system according to claim 7 wherein the former is
laminar.
10. An antenna system according to claim 1 wherein each antenna
element is a patch antenna element.
11. A radar system comprising an antenna system according to claim
1.
12. A radar system according to claim 11 wherein at least one of
the first and second phase-controllers comprises a Rotman lens.
13. A radar system according to claim 12 wherein both the first and
second phase-controllers each comprise a Rotman lens.
14. A radar system according to claim 13 further comprising first
and second RF switches coupled to the first and second Rotman
lenses respectively.
15. A radar system according to claim 14 further comprising a
monolithic microwave integrated circuit (MMIC) operable to provide
a transmission signal to each RF switch.
16. A radar system according to claim 11 wherein the radar system
is a FMCW radar system.
17. A radar system according claim 16 further comprising a RF
oscillator, a DDS arranged to provide a frequency-modulated signal
and a mixer arranged to mix respective outputs of the RF oscillator
and the DDS to provide a FMCW signal for transmission, and wherein
the clock signal of the DDS is derived from the Rb oscillator
output.
18. A radar system according to claim 17 comprising one or more
ADCs arranged to digitise received signals and wherein the clock
signal of each ADC is derived from the RF oscillator output.
19. A radar system according to claim 17 and further comprising a
frequency-divider arranged to frequency-divide the output of the RF
oscillator to generate the, or each, clock signal.
20. A radar system according to claim 17 wherein the RF oscillator
is a free-running DRO.
21. A radar system according to claim 11 and arranged to produce
from the antenna array a transmitted signal having a frequency
which is a function of transmission direction.
22. A radar system according to claim 11 wherein the radar system
is monostatic.
23. A radar system according to claim 11 wherein the radar system
is bistatic.
24-26. (canceled)
Description
[0001] The invention relates to antenna systems and to radar
systems.
[0002] Radar systems for certain applications are required to have
the capability to produce more than one radar beam pattern in order
to perform more than one type of detection and ranging. For
example, an automotive radar system may be required to produce a
long-range beam pattern having a relatively narrow angular extent
in azimuth for use in cruise control on motorways, and also a
short-range beam pattern having a wider angular azimuthal extent
for use in a parking sensor system and to monitor nearby vehicles
for the purpose of collision avoidance. Existing automotive radar
systems of this type use two separate radar sub-systems to provide
such beam patterns; see for example "A Wideband Millimetre-Wave
Front-End for Automotive Radar" by J. C. E. Mayock et al, 1999 IEEE
MTT-S Digest. This approach requires four antenna sub-systems if
the two radar sub-systems are bistatic. Accommodation of four
antenna sub-systems within a vehicle body places significant
constraints on vehicle body shape and/or size. Also, each
sub-system requires dedicated operating electronics because the
transmitted frequencies of the short- and long-range beam patterns
are different. (Typically 24 GHz is used for the short-range beam
and 77 GHz for the long-range beam). The complexity and size of
these existing automotive radar systems results in substantial cost
both to manufacturers and consumers, impeding the take-up of
automotive radar technology. Similar problems arise in other
applications where antenna and radar systems having more than one
beam pattern are required.
[0003] A first aspect of the invention provides an antenna system
comprising an array of antenna elements, the array comprising a
plurality of groups of antenna elements wherein each group
comprises one or more antenna elements arranged in series, and
wherein the system further comprises first phase-control means for
performing the function of applying respective phase-shifts to
transmitted or received signals passed to or received from each of
said groups to provide beamforming and second phase-control means
for performing said function with respect to a sub-set of said
groups.
[0004] A single antenna system of the invention allows two radar
beam patterns having different spatial characteristics to be
produced, thus reducing the number of antenna systems needed to
provide such functionality compared to prior art systems. An
antenna system of the invention may be used for transmission,
reception or both transmission and reception. By operating the
array, and the sub-set of groups, at substantially the same
frequency the invention allows a reduction in the cost and
complexity of operating electronics used with the antenna
system.
[0005] One or more additional sub-sets of groups of antenna
elements may be defined using further respective phase-shifting
means, providing for one or more additional beam patterns to be
generated.
[0006] Although arrangements of switches and conventional
phase-shifters may be used to carry out phase-control, preferably
either the first or the second phase-control means is a Rotman
lens. More preferably, both the first and second phase-control
means are Rotman lenses. Rotman lenses are described in, inter
alia, the proceedings of the 22.sup.nd International Communications
Systems Satellite Conference & Exhibition 2004 (American
Institute of Aeronautics & Astronautics), paper AIAA 2004-3196
by P. S. Simon, and are advantageous because they can be realised
in planar, cheap and reliable form and are less affected by
aberration errors than other phase-control devices.
[0007] Conveniently, the array of antenna elements is substantially
rectangular, and each of the groups of antenna elements is a row or
column of the array. This provides for simpler manufacture.
[0008] In one embodiment, the sub-set of groups of antenna elements
is made up of contiguous rows or columns of the array.
[0009] Preferably the array of antenna elements is substantially
planar, allowing the array to be placed behind a registration plate
of a vehicle, for example.
[0010] For ease of manufacture, preferably the array of antenna
elements and the Rotman lenses are mounted on a common former. For
example, the former may be substantially cuboid in shape, with the
first and second Rotman lenses mounted on opposite faces of the
cuboid former and the array of antenna elements mounted on a face
of the cuboid former adjacent of the faces mounting the Rotman
lenses. Alternatively the former may be laminar with the array of
antenna elements, and the Rotman lenses, mounted on the same side,
or opposite sides, thereof. Manufacture of an antenna system of the
invention is further simplified if each antenna element is a patch
antenna element.
[0011] A second aspect of the invention provides a radar system
comprising an antenna system of the invention. For reasons
mentioned above, preferably one of the phase-control means is a
Rotman lens, or, more preferably, both of the phase-control means
are Rotman lenses. In order to allow rapid directional scanning of
the radar pattern of the whole array or the sub-set of groups (in
either transmission or reception), inputs to the Rotman lenses may
be coupled to respective RF switches. A RF signal for transmission
is preferably provided by a monolithic microwave integrated circuit
(MMIC) operable to provide the signal to either of the RF switches,
as a MMIC may be integrated with the RF switches.
[0012] A radar system of the invention may be a
frequency-modulated, continuous-wave (FMCW) radar system. In order
to provide low-phase noise on transmit and highly coherent
operation (and hence high range accuracy) at low cost, preferably
the radar system comprises an RF oscillator, a direct digital
synthesiser (DDS) arranged to provide a frequency-modulated signal
and a mixer arranged to mix respective outputs of the RF oscillator
and the DDS to provide a FMCW signal for transmission, wherein the
clock signal of the DDS is derived from the RF oscillator. By
locking the DDS to the RF oscillator, a free-running source (e.g. a
free-running dielectric resonator oscillator (DRO)) may be used
because any jitter in the output of the RF oscillator then
corresponds to the same jitter in the DDS clock signal.
Additionally, in embodiments of the invention in which one or more
analogue-to digital converters (ADCs) are provided to digitise
received signals, the clock signal for each ADC is preferably
derived from the RF oscillator. The various clock signals may be
obtained by frequency-dividing the output of the RF oscillator. Use
of a free-running source as the RF oscillator, rather than a
phase-locked source, provides optimum phase noise at offset
frequencies that cause most effect in FMCW radars (typically 100
kHz and 1 MHz from the carrier frequency). The use of a DDS as
described above provides very high frequency-sweep linearity and
hence very high range resolution.
[0013] In automotive radar applications it is important to avoid
the problem of interference between radars systems of vehicles
which are adjacent or nearly adjacent and travelling in the same
direction, as occurs for example on motorways when vehicles are
moving in adjacent lanes. If automotive radar systems fitted to
adjacent vehicles use the same frequency then each system will
return spurious results. To avoid this problem, the frequency of
radiation transmitted from a radar system of the invention is
preferably a function of transmission direction.
[0014] A radar system of the invention may be monostatic, in which
case a single antenna system of the invention is needed for both
transmission and reception, or bistatic, in which case two antenna
systems of the invention are required. The same operating
electronics can be used to operate the whole array of antenna
elements and to operate the sub-set of groups of antenna
elements.
[0015] Embodiments of the invention are described below by way of
example only and with reference to the accompanying drawings in
which:
[0016] FIGS. 1 & 2 show perspective views of an antenna system
of the invention;
[0017] FIG. 3 shows an array of patch antenna elements comprised in
the antenna system of FIGS. 1 and 2;
[0018] FIG. 4 shows drive electronics for use with the antenna
system of FIGS. 1 & 2 to provide azimuthal scanning in
transmission or reception; and
[0019] FIGS. 5 & 6 show advantageous arrangements for
generating a transmitted FMCW signal and for digitising radar
returns within a radar system of the invention.
[0020] Referring to FIGS. 1, 2 and 3, an antenna system of the
invention is indicated generally by 100. The antenna system 100
comprises a substantially cuboid former 114 mounting first 108 and
second 116 Rotman lenses on opposite faces thereof and a
rectangular array 102 of antenna elements on a face of the former
114 adjacent to the faces mounting the Rotman lenses 108, 116. The
array 102 comprises 69 groups of patch antenna elements, each group
comprising a linear array of 11 elements connected in series
forming a column of the array 102. Rotman lens 108 has 69 outputs
each of which is coupled to a respective group of patch antenna
elements via a connecting line. The 69 connecting lines are
indicated collectively by 106. Rotman lens 116 has 19 outputs, each
of which is coupled by a connecting line to a respective column of
antenna elements in a sub-set 104 of columnar groups of the array
102, the sub-set being the central 19 columns (shown shaded in FIG.
3) of the array 102. The 19 connecting lines coupling outputs of
the lens 116 to respective columns in the sub-set 104 of groups of
antenna elements of the array 102 are indicated collectively by
112. Connecting lines to the various inputs of the Rotman lenses
108, 116 are indicated by 110, 118 respectively.
[0021] The antenna system 100 may operate either as a transmitter
or a receiver, or both when used in a monostatic radar system. A
long-range beam pattern with a narrow angular extent in azimuth may
be produced by operating the system 100 so that only the sub-set
104 of groups of antenna elements are activated. The
transmit/receive direction of the system in this mode of operation
may be varied in azimuth by applying a transmission signal to an
appropriate input of lens 116 in the case of transmission, or by
processing a signal from an appropriate input of the lens 116 in
the case of reception. The azimuthal direction of a short-range
beam pattern may be varied similarly, i.e. by applying a
transmission signal to an appropriate input of lens 108 in the case
of transmission, or by processing signals from an appropriate input
of the lens 108 in the case of reception.
[0022] FIG. 4 schematically illustrates an arrangement for
producing a scanning, transmitted, long-range radar beam pattern
using the antenna system 100. Input lines 118 to the Rotman lens
116 (the outputs 112 of which are connected to the sub-set 104 of
groups of the array 102) are connected via an alumina drop-in unit
120 to an RF switch 122. A monolithic microwave integrated circuit
(MMIC) 124 provides an RF transmission signal and a
direction-scanning signal to the RF switch 122. At a particular
instant, the RF transmission signal appears on a particular output
of the RF switch 122 according to the status of the
direction-scanning signal. The RF transmission signal is applied to
the Rotman lens 116 via a particular input 118. Drive signals
appear at each of the outputs 112 of the Rotman lens 116 with
appropriate phasing to generate a plane wave having an azimuthal
transmission direction corresponding to that particular input of
the Rotman lens 116. A second RF switch and drop-in unit (not
shown) are provided for the Rotman lens 108 to allow transmission
of a short-range beam pattern from the whole of the array 102 of
antenna elements. The MMIC 124 is arranged for switching between
the RF switches so that a long- or short-range beam may be
transmitted as required.
[0023] The arrangement shown in FIG. 4 may also be used for
reception. For example, a direction-scanning signal applied to RF
switch 122 provides for each of the lines 118 to be coupled through
the RF switch in turn, corresponding to scanning of the receive
direction in azimuth. Switching means may be provided to allow
switching between lenses 108, 116 so that reception may be carried
out using either the whole array 102 or using the sub-set 104 of
antenna elements, as desired.
[0024] Two separate arrangements of the type shown in FIG. 4 may be
used (one for transmission and one for reception) in a bistatic
radar system of the invention.
[0025] FIG. 5 shows an arrangement for providing high range
range-accuracy in a FMCW radar incorporating an antenna system of
the invention. A free-running DRO 132 operating at 9200 MHz is
coupled to a mixer 134. Output from the DRO 132 is also
down-converted by a first frequency-divider 136 to provide a clock
signal to a DDS 138 which is arranged to output a signal having a
frequency which periodically increases from 200 MHz to 250 MHz in a
sawtooth form, as shown in the Figure. Mixing of the DDS and DRO
outputs at the mixer 134 provides an FM RF transmission signal
which also has a sawtooth frequency as a function of time, sweeping
from 9400 MHz to 9450 MHz. Output from the first frequency-divider
136 is passed to a second frequency-divider 140 which provides a
further down-converted signal to a complex programmable logic
device (CPLD) 142 which in turn provides a clock signal to an ADC
144 which digitises signals received from the antenna system of the
radar system. By locking the various clock signals to a single
reference (DRO 132) the reference can be free-running because any
jitter in the reference corresponds to the same jitter on the clock
signals, thus providing highly coherent operation.
[0026] FIG. 6 show an alternative to the FIG. 5 arrangement, in
which the output of a mixer 154 is up converted to provide an RF
transmission signal having a frequency which is an order of
magnitude greater than that of the arrangement shown in FIG. 5.
* * * * *