The present invention relates to the field of radars, in particular airborne
radars, comprising a transceiver antenna including a plurality of radiating
5 elements distributed over a surface and configured for transmitting and
receiving electromagnetic waves, said radar comprising an antenna gain
control unit.
It is known, in reference to figure 1 showing an aircraft 20 embedding
a radar emitting electromagnetic waves 31, that the echoes coming from the
10 surface 30 (ground, sea, etc.) located below the aircraft 20 and reflecting the
emitted electromagnetic waves 31 saturate the radar on reception when it is
located at low altitude, that the echoes coming from the part of the emitted
wave 31 having traveled a distance D0 from the radar 20 to the reflective
surface 30 will have higher amplitudes and be less delayed than the echoes
15 coming from the reflection of a part of the emitted wave 31 having traveled a
longer distance D1 from the radar 20 to the reflective surface 30.
Curve L1 in figure 2 shows a graph providing the general appearance,
on the y-axis, of the power of the echoes received by the antenna of the radar
as a function, on the x-axis, of the distance D traveled by the emitted wave
20 31 between the radar and the reflective surface (or similarly of the time delay
between the transmission of a wave and the reception by the radar of the
echo of this wave portion D = c/2. , where c is the celerity); the saturation
zone is shown schematically by reference Zs.
To avoid the situation at the input of the radar caused by the high power
25 of the echoes received by the radar at small distance D or delay and also
to compensate the corresponding amplitude variabilities, it is known to have
a Sensitivity Time Control (STC) attenuator, which performs two functions:
- attenuating the gain of the receiving channel to ensure that the
maximum level of the received signals is not in the saturation
30 zone of the receiver;
- further performing gain compensation processing, called STC
compensation processing hereinafter, making it possible to
compensate for the level variation of the echoes received as a
function of the delay , therefore of the distance D, by adjusting
2
the gain of the receiver with an inverse gain law relative to the
variation of the levels as a function of (which has form
, with α a real number).
This STC attenuator must therefore be placed, in order to avoid
5 saturation, very far upstream of the receiving channel of the radar, on the
radiofrequency signal received at the antenna, which results in increasing
the noise factor of the reception of the radar, this effect then also having to
be compensated in real time as a function of the distance D (of the delay
). Furthermore, such an attenuator must be calibrated in frequency and in
10 temperature to compensate the gain dispersions. Such an STC attenuator
solution is further particularly complex to deploy in the modern architectures
of radars, which have an increasingly high number of reception channels.
To that end, according to a first aspect, the invention proposes a radar
of the aforementioned type, characterized in that the antenna gain control
15 unit is configured for feedback controlling, through an adjustment loop, the
antenna gain in transmission and/or reception by a turning on or off radiating
elements of the plurality of radiating elements, in order to keep the reception
level of the electromagnetic waves below a determined threshold below the
saturation zone of the radar.
20 The invention thus makes it possible to maintain a level of reception
appropriate for the performance of the receiver, and in particular to avoid the
saturation of the radar on reception.
It thus uses the fact that, in reference to figure 2, the lower the height
h of the moving device 20 is relative to the surface 30, the higher the power
25 of the close echoes will be and the lower the incidence α of the emitted wave
31 will be relative to the surface 30, the greater the spreading out over time
of the ground clutter (and therefore if applicable the saturating levels) is.
In embodiments, the radar according to the invention further includes
one or more of the following features:
30 - the antenna is configured for emission from a given height relative to
a given surface and at a given incidence angle, the gain control unit is
configured, in said adjustment loop, for performing at least one of the
following operations:
3
- determining the deviation between the current level of the
received electromagnetic wave and a reference level, in order to
determine the gain adjustment as a function of said deviation and to
command the turning off or on of radiating elements in transmission
5 and/or reception based on said determined gain adjustment;
- determining at least one set of value(s) comprising at least
one value among said given height and said given incidence angle,
in order to determine the gain adjustment based on each value of
said determined set of value(s) and to command the turning off or
10 on of radiating elements in transmission and/or reception based on
said determined gain adjustment;
- the gain control unit is configured, in said adjustment loop, for
adjusting the gain according to a function calculating the gain value based
on at least each value of said set of value(s), said function being a decreasing
15 function of said value when the value is the height and an increasing function
of the value when the value is the incidence angle;
- the gain control unit is configured for modifying the gain according to
at least one operation among a nonzero power modification command
emitted by each radiating element and a command to turn on or off at least
20 some of said radiating elements;
- the radar comprises a compensating module configured for
attenuating the amplitude of a received electromagnetic wave based on the
distance traveled to said surface by said electromagnetic wave, said
compensating module being configured for performing this attenuation on
25 digital samples of the received electromagnetic waves based on the distance
and/or for performing this attenuation by a command to turn on or off at least
some of said radiating elements determined based on said distance.
According to a second aspect, the present invention proposes a flying
device comprising an embedded radar according to the first aspect of the
30 invention.
According to a third aspect, the present invention proposes a
processing method in a radar embedded in a flying device, the radar
comprising a transceiver antenna including a plurality of radiating elements
4
distributed over a surface and configured for the transmission and reception
of an electromagnetic wave, said method comprising the following steps:
- transmitting an electromagnetic wave from the antenna and receiving an
electromagnetic wave by the antenna;
5 said method being characterized in that it comprises the following step
implemented by an electronic gain control unit of the radar:
- feedback controlling, through an adjustment loop, the antenna gain in
transmission and/or reception by a turning on or off radiating elements of the
plurality of radiating elements, in order to keep the reception level of the
10 electromagnetic waves below a determined threshold below the saturation zone of
the radar.
In embodiments, the method according to the invention further includes
one or more of the following features:
- said adjustment loop comprises at least one of the steps among
15 steps a and b:
a/ determining the deviation between the current level of
the received electromagnetic wave and a reference level,
determining the gain adjustment as a function of said deviation
and commanding the turning off or on of radiating elements in
20 transmission and/or reception based on said determined gain
adjustment;
b/ the transmission having taken place from a given
height relative to a given surface (30) and at a given incidence
angle, determining at least one set of value(s) comprising at
25 least one value among said given height and said given
incidence angle, determining the gain adjustment based on each
value of said determined set of value(s) and commanding the
turning off or on of radiating elements in transmission and/or
reception based on said determined gain adjustment;
30 - said adjustment loop comprises adjusting the gain according to
a function calculating the gain value based on at least each
value of said set of value(s), said function being a decreasing
function of said value when the value is the height and an
5
increasing function of the value when the value is the incidence
angle.
According to a fourth aspect, the present invention proposes a
processing method that can be broken down into a computer program
5 comprising software instructions which, when executed by a computer, carry
out a method as defined above.
These features and advantages of the invention will appear upon
reading the following description, provided solely as an example, and done
in reference to the appended drawings, in which:
10 [Fig 1] figure 1 shows a view of an aircraft embedding a radar according
to one embodiment of the invention;
[Fig 2] figure 2 is a view of a graph showing the electromagnetic wave
power received by a radar based on the distance traveled by a wave
received as an echo or the corresponding propagation time, in particular
15 in one embodiment of the invention;
[Fig 3] figure 3 is a schematic view of a radar in one embodiment of the
invention;
[Fig 4] figure 4 is a schematic view of an antenna in one embodiment
of the invention;
20 [Fig 5] figure 5 is a flowchart of steps implemented in one embodiment
of the invention.
Figure 3 shows a radar 10 in one embodiment of the invention.
The radar 10 is configured, when it is embedded in a flying device such
as an aircraft 20, for detecting the presence of target objects such as
25 airplanes, boats, or rain, and/or determining the position as well as the speed
of such target objects. Indeed, the waves sent by the radar 10 are in
particular reflected by the target object, and the return signals (called radar
echo) are captured and analyzed by the radar.
The radar 10 includes a transceiver antenna 11, an antenna gain
30 control unit 12, a radar transmission unit 10E and a radar reception unit 10R.
The transceiver antenna 11 is configured for transmitting an
electromagnetic wave at a pointing angle and for receiving an
electromagnetic wave.
6
In embodiments, the antenna 11 is an active electronically scanned
array: in reality, the antenna is a set of several (typically several hundred)
radiating elements, called subarrays or elementary arrays; these elementary
arrays are independent of one another and each have their own source. In
5 embodiments, the antenna 11 is AESA (Active Electronically Scanned
Array), MIMO (Multiple Input Multiple Output), etc.
In one considered embodiment, the antenna 11 is for example made
up of a phased array.
In the considered embodiment, the antenna 11 comprises, in reference
10 to figure 4, a surface 18 and a plurality of elementary antennas 180
distributed on said surface 18, arranged in a matrix and here drawing a
substantially circular shape. In other embodiments, the shape of the
transmission surface is different: square, rectangular, triangular, etc.
Each elementary antenna 180 constitutes a radiating element
15 configured for transmitting, at a given frequency and with a given phase, its
own electromagnetic wave in a direction normal to the surface 18.
In the embodiment considered here, each radiating element transmits
at the same frequency with an amplitude and a phase specific to each
radiating element.
20 In embodiments, the beam(s) of the antenna 11 is/are controlled in
terms of angular position, etc.
The radar 10 includes a transmission unit 10E configured for generating
the wave to be transmitted by the antenna 11. The transmission unit 10E for
example comprises, in a known manner, a permanent oscillator, an amplifier
25 and a modulator (not shown). In one embodiment, it is further configured for
commanding the beam(s) of the antenna 11 in terms of position, movement,
etc.
The radar 10 includes a reception unit 10R configured for processing a
wave received by the antenna 11 and coming from the reflection of the
30 transmitted wave, in order to determine the existence (and/or the position
and/or the speed) of one or several targets.
In one embodiment, the reception block 10R includes a processing
chain to which the output signal from the antenna is supplied; the chain
includes the following successive modules: a channel forming module, a
7
module for amplification of each of the microwave frequency channels, a
module for transposition to intermediate frequency, an encoding module and
a digital processing module.
In the considered embodiment, the radar 10 further includes a control
5 unit 12 of the antenna gain 11 in reception and/or transmission; in the specific
considered case, the antenna gain control unit 12 is an EIRP (Equivalent
Isotropically Radiated Power) control unit 12.
The EIRP control unit 12 comprises a regulating loop in order to keep
the reception level of said electromagnetic wave below a determined
10 threshold (chosen so that it is below the saturation level of the receiver)
through an adjustment loop of the EIRP of the transceiver antenna; it is
configured for triggering changes of the EIRP used for the transmission of an
electromagnetic wave by the antenna 11.
The regulating loop can be implemented in different ways, which may
15 optionally be combined, two of which are explained hereinafter.
In a first embodiment, the EIRP control unit 12 is configured, for
example before each transmission of a new radar pulse, for determining the
current level of the signal received by the antenna 11 of the radar 10
corresponding to the echoes of the preceding emitted pulse. Then, the EIRP
20 control unit 12 is configured for comparing this level with a reference level
Pref (for example Pref = 0 dBm), the deviation determined after this
comparison making it possible to deduce the desired attenuation Att
therefrom and to trigger the changes to be made to the EIRP based on the
attenuation to be provided. For example, the determined current level is that
25 of the maximum signal measured at the end of the receiving channel, after
the digital processing. Such a regulating loop makes it possible to keep the
EIRP around the set value, here 0 dBm, and therefore makes it possible to
keep the level of the signal in a zone appropriate for the performance of the
receiver, and in particular to avoid saturating the receiver.
30 For example, if the maximum received level at the end of the receiving
channel has a deviation of 6 dB above the reference level, the level is brought
back to the reference level, for example as described later (here for example
by turning off half of the elementary antennas).
8
In a second embodiment, the EIRP is adjusted by the regulating loop
based on one or several parameters among the transmission height of the
electromagnetic wave and the incidence angle α of the transmitted wave
relative to the reflective surface.
5 In such an embodiment, the current value of the transmission height is
provided to the EIRP control unit 12 by navigation instruments of the aircraft
or determined by the RADAR in one embodiment (air/ground telemeter
and/or the current value of the incidence angle α is provided to the EIRP
control unit 12 (α is for example a usage setpoint of the RADAR determined
10 by the usage modes of the RADAR or imposed by the pilot of the aircraft.
In one embodiment, the incidence angle refers to the angle between
the axis of the RADAR beam and the horizon.
In one embodiment, the EIRP control unit 12 comprises a memory 13
and a microprocessor 14. The memory 13 comprises software instructions
15 which, when executed on the microprocessor 14, implement the steps for
which the EIRP control unit 12 is responsible that are described in reference
to figure 5 hereinafter.
In one embodiment, the EIRP control unit is integrated within a digital
card of the COTS type.
20 In another embodiment, the EIRP control unit 12 is made in the form of
a programmable logic component, such as an FPGA (Field Programmable
Gate Array), or in the form of a dedicated integrated circuit, such as an ASIC
(Application Specific Integrated Circuit).
Figure 5 describes a set 100 of steps for implementing the adjustment
25 of the antenna gain in transmission and/or reception, in the specific
considered case, here for adjusting the EIRP, through a regulating loop in
one embodiment, during an operational phase of the radar 10 implemented
during a flyover of an analysis zone by the aircraft 20 embedding the radar
10: the radar 10 emits an electromagnetic wave using the antenna 11 toward
30 a surface 30 and receives the corresponding radar echoes via the antenna
11, which it then processes.
In a step 101, the antenna gain control unit 12 determines whether
antenna gain adjustments must be implemented in order to keep the
9
reception level of said electromagnetic waves below a determined threshold,
and thus to stay outside the saturation range of the receiver.
In a step 102, the antenna gain control unit 12 triggers, with the
antenna 11, the implementation of the gain change thus determined.
5 In the particular case of EIRP control, in the first embodiment, before
the emission of a new radar pulse, the EIRP control unit 12 determines the
deviation between the current power of the signal received by the receiver of
the radar corresponding to the echoes from the previous pulse and the
reference power, then it determines the change in EIRP to be implemented
10 based on this deviation.
In the second embodiment, the EIRP control unit 12 receives the
updated value of the height h of the radar 10 relative to the surface being
overflown and/or the updated value of the incidence angle α.
The EIRP control unit 12, after receiving the updated value(s),
15 determines a change in EIRP 11 based on this updated value (or these
updated values).
In a step 102, the EIRP control unit 12 triggers, with the antenna 11,
the implementation of the EIRP change thus determined.
The present invention thus makes it possible to modulate the EIRP in
20 transmission based on the level of clutter.
There are also different solutions for adjusting the EIRP: for example,
by adjusting the power transmitted by each elementary antenna 180, by
increasing or decreasing the power emitted by each elementary antenna 180
emitting a nonzero power and/or, as considered hereinafter, by turning off or
25 on a certain number of these elementary antennas.
In one embodiment, in order to decrease the EIRP of the antenna 11
shown on the left in figure 4 where each elementary antenna 180 is active,
the EIRP control unit 12 commands the placement in the inactive state (zero
emitted power) of the elementary antennas 180 located on the periphery of
30 the transmission surface 18: the elementary antennas then deactivated in
transmission are shown in black in the right part of figure 4. This results in
broadening the wave beam and decreasing the total radiated power.
In another embodiment, the reverse is commanded: only the
elementary antennas 180 located in the peripheral ring remain active, while
10
the central elementary antennas are deactivated: the directivity and the
angular width of the beam are then similar to that of the antenna 11 with all
of its elementary antennas active, the reduction in EIRP then being in the
ratio Na/NT as described below.
5 Or:
a0 the effective surface of an elementary antenna;
Nk the number of elementary antennas 180 on the surface 18;
λ: the wavelength;
it is known that the gain (linear) in the pointing axis, perpendicular to
10 the surface 18, is Gk:
𝐺𝑘 =
4.𝜋.𝑎0
𝜆
2
. 𝑁𝑘
(Nb: the misaligned gain of φ is: Gd =
4.π.a0
λ
2
.Nk. Cos φ).
Each elementary antenna 180 delivers a power 𝑝.
The total power 𝑃𝑘 = 𝑝. 𝑁𝑘
15 The EIRP of the antenna 11 is equal to 𝑃𝑘.𝐺𝑘.
The determination of the number Na of active elementary antennas to
be kept (and therefore the number of elementary antennas to be deactivated
Nd with Nd = NT – Na is for example done by the EIRP control unit 12 using
20 the following formula:
𝑁𝑎 = √
𝑁𝑇
2
𝐴𝑡𝑡
Where:
NT is the total number of elementary antennas 180;
Na is the number of active elementary antennas 180;
25 Att is the attenuation ratio of the desired power of the reception signal
(in dB).
The attenuation, in the first embodiment, is determined based on the
deviation determined between the current reception level and the reference
level.
30 For example, in a case where h is 1000 m, the incidence and the
aperture of 5°, the regulating loop thus makes it possible, in one particular
11
embodiment, to vary the channel gain from 135 dB to 143 dB according to
D, in order to contain the level of clutter around 0 dBm, or a variation of 8 dB.
To determine what EIRP adjustment is needed, the maximum received
5 power is determined, corresponding to the least delayed signal.
For example, a clutter level at 0 dBm is desired, for the channel gain in
the receiver to be 140 dB and the max level of the signal to be -134 dB, the
EIRP must then be decreased by 6 dB, or a linear decrease of 4, or Na =
500.
10 In the second described embodiment, the attenuation is determined
based on value tables defining the attenuation value based on α and h (for
example from STC tables that also depend on h and α).
Example: if NT = 1000 and Att = 2, then the number of elementary
antennas to be kept active is Na, with
𝑁𝑎 = √
10002
2
15 = 707
This formula yielding Na is easy to demonstrate. As seen above, the
EIRP is equal to 𝑃𝑘.𝐺𝑘 = 𝑝. 𝑁𝑘
2
.
4.𝜋.𝑎0
𝜆
2 = 𝑝. 𝑁𝑘
2
. 𝐶𝑡𝑒. This means that, calling
EIRPT the EIRP of the antenna 11 when all (NT) of its elementary antennas
180 are active and EIRPa the EIRP of the antenna 11 when only Na of its
20 elementary antennas 180 are active:
𝐸𝐼𝑅𝑃𝑇= 𝑝. 𝑁𝑇
2
. 𝐶𝑡𝑒
𝐸𝐼𝑅𝑃𝑎= 𝑝. 𝑁𝑎
2
. 𝐶𝑡𝑒; and that therefore
𝐴𝑡𝑡 =
𝐸𝐼𝑅𝑃𝑇
𝐸𝐼𝑅𝑃𝑎
=
𝑁𝑇
2
𝑁𝑎
2
.
The surface of the antenna is 𝑆𝑘 = 𝑁𝑘. 𝑎0; its diameter is 𝐷𝑘 = 2. √
𝑁𝑘
.𝑎0
4.𝜋
25
in the case of a round surface;
𝐺𝑘 = 6. (
𝐷𝑘
𝜆
)
2
The aperture angle is 𝜃𝑘 = 70.
𝜆
𝐷𝑘
. For a constant α, when h increases,
the level of the received signal decreases, Att decreases, the EIRP adapted
30 according to the invention increases.
12
For a constant h, when α (considered in absolute value) increases
(tends toward plumb), the level of the received signal increases, therefore,
according to the invention the value Att increases, the EIRP decreases.
The EIRP is therefore a decreasing function of h and an increasing function
5 of lαl.
In one embodiment, the receiving unit 10R further includes, in the
embodiment, a module of the STC type performing STC compensating
processing, i.e., compensating the variability of the amplitudes of the digital
samples of the received echo signals based on the distance D and the time
10 t. This STC processing is for example done after encoding, in the digital
processing module, therefore far downstream, which reduces the noise
relative to the prior art.
Curve L2 in figure 2 shows a graph providing the general appearance,
on the y-axis, of the power of the echoes received by the antenna of the radar
15 as a function, on the x-axis, of the distance D traveled by the emitted wave
31 between the radar and the reflective surface (or similarly time t) after
implementation of the EIRP attenuation in transmission according to the
invention to avoid saturating the input of the radar 10, for a height and an
incidence identical to those of curve L1 corresponding to a maximum EIRP.
20 In one embodiment, the configuration of the elementary antennas in
reception remains unchanged, while the configuration of the elementary
antennas in transmission is adjusted according to the invention.
Other embodiments of the invention can, however, be implemented,
aside from the limitation of the maximum received level by EIRP (in
25 transmission as a result) with STC compensation processing by digital
processing of the signal as described above, for example, in embodiments
that can optionally be combined with the previous one and/or with one
another:
- limiting the maximum received level by limiting the antenna gain in
30 reception by the antenna gain control unit 12 below the saturation threshold
of the radar 10 (by turning off/on elementary antennas) and performing the
STC compensation by digital processing of the received signal;
- limiting the maximum received level below the saturation threshold of
the radar 10 and performing the STC compensation processing by the
13
antenna gain control unit 12, both by adjustment by the latter of the antenna
gain upon reception:
either by applying preestablished STC compensation laws
depending on the altitude and the incidence,
5 or by regulating the received level around a reference value
chosen to be in a work zone compatible with the characteristics of
the receiver in particular outside its saturation zone;
- limiting the maximum received level below the saturation threshold of
the radar 10 by limiting the EIRP (in transmission as a result) by the antenna
10 gain control unit 12 as described above for example and performing the STC
compensation by the antenna gain control unit 12 by further adjusting the
antenna gain on reception.
The last two listed embodiments only require that the elementary
antennas be controllable separately in transmission and reception.
15 In the embodiments with adjustment of the antenna gain in reception
to prevent the saturation of the receiver, the gain adjustment in reception is
iterated for example upon each new string of received echoes, that is to say
in a new distance slot of a sequence of distance slots considered to
correspond to the echoes successively received in a same emitted pulse.
20 In one embodiment, in reference to figure 4, the gain control unit 12 in
transmission and/or reception is configured for adjusting the antenna gain in
transmission and/or reception stepwise by first activating only the elementary
antennas in transmission and/or reception in the ring between the circles C1
and C2, then next by further activating only the elementary antennas
25 between C2 and C3 if necessary, then by activating only the elementary
antennas between C3 and C4, if necessary. This arrangement, similar to the
operation of a camera diaphragm, makes it possible to vary the gain without
changing the aperture of the antenna. Alternatively, the rings can be turned
on successively on the contrary by starting from the center moving toward
30 the outside, which changes both the gain and the aperture (with the central
ring or the central disc only: the EIRP is minimal, the aperture is maximal,
then the gain increases and the aperture decreases with the number of rings
activated). In one embodiment, to perform STC compensation processing,
the outermost ring, that is to say between C1 and C2, is activated in
14
reception, then the other rings are activated in turn starting from the
outermost ring to the innermost ring.
The width of each ring can be defined such that the gain pitch is
constant; to do this, the number of elementary antennas activated on each
5 ring must be the same; the width of the ring is inversely proportional to the
diameter of the ring.
The width of the finest ring is defined by the presence of at least one
module for the smallest possible ring width.
This number of modules determines the width of the following rings,
10 and as a result, their number.
In summary, the method takes place as follows as a function of time:
For a transmission phase:
the modules located in the concentric rings of the antenna in
15 transmission are activated to adjust the gain of the antenna by switching of
the rings in a contiguous manner (like a diaphragm), so as to avoid the
saturation of the receiver. The gain of the antenna in transmission is
[therefore] adjusted upon each RADAR recurrence with a constant value
over the entire duration of the transmission impulse.
20
For a reception phase:
the modules located in the concentric rings of the antenna in reception
are activated to adjust the gain of the antenna by switching of the rings in an
adjacent manner (like a diaphragm), so as to compensate the amplitude
25 variation of the reception echoes as a function of time (or distance). The gain
will therefore be adjusted dynamically during reception so as to have a
minimum gain at the beginning of reception and maximum at the end, as is
the case with an STC variable attenuator.
30
NB:
In the transmission phase, it is also possible to adjust the gain of the
transmission antenna by first activating the smallest rings (still in a
15
contiguous manner). In this case, the aperture of the antenna will not be
constant.
The invention makes it possible to eliminate the STC attenuators
5 conventionally arranged at the head of microwave frequency receivers to
prevent saturation by the signal returning from nearby ground, and thereby
to improve the noise factor of the receiving channel.
This invention lightens the physical architecture of the RADARs, as
well as the associated adjustments/calibrations, and therefore decreases
10 their costs.
It also lightens the processing by eliminating the calibrations of the STC
attenuators.
The stealth of the RADAR is further improved, due to the decrease in
the EIRP rather than by decreasing the gain in reception.
15 It will be noted that the invention has been described above in
reference to a radar embedded in an aircraft. In other embodiments, the
radar 10 during its use for target detection purposes is embedded in other
flying devices, which may be moving or stationary, such as drones,
helicopters, balloons, etc.

I/We Claim:
1. A radar (10) comprising a transceiver antenna (11) including a
plurality of radiating elements (180) distributed over a surface (18) and
5 configured for transmitting and receiving an electromagnetic wave, said
radar comprising an antenna gain control unit (12), wherein the antenna gain
control unit is configured for feedback controlling, through an adjustment
loop, the antenna gain in transmission and/or reception (12) by turning on or
off radiating elements of the plurality of radiating elements, in order to keep
10 the reception level of the electromagnetic waves below a determined
threshold below the saturation zone of the radar.
2. The radar (10) according to claim 1, wherein the antenna is
configured for emission from a given height (h) relative to a given surface
15 (30) and at a given incidence angle (α), the gain control unit is configured, in
said adjustment loop, for performing at least one of the following operations:
- determining the deviation between the current level of the received
electromagnetic wave and a reference level, in order to determine the gain
adjustment as a function of said deviation and to command the turning off or
20 on of radiating elements in transmission and/or reception based on said
determined gain adjustment;
- determining at least one set of value(s) comprising at least one value
among said given height (h) and said given incidence angle (α), in order to
determine the gain adjustment based on each value of said determined set
25 of value(s) and to command the turning off or on of radiating elements in
transmission and/or reception based on said determined gain adjustment.
3. The radar (10) according to claim 1 or 2, wherein the gain control
unit (12) is configured, in said adjustment loop, for adjusting the gain
30 according to a function calculating the gain value based on at least each
value of said set of value(s), said function being a decreasing function of said
value when the value is the height and an increasing function of the value
when the value is the incidence angle.
17
4. The radar (10) according to any one of the preceding claims,
wherein the gain control unit (12) is configured for modifying the gain
according to at least one operation among a nonzero power modification
command emitted by each radiating element (180) and a command to turn
5 on or off at least some of said radiating elements.
5. The radar (10) according to any one of the preceding claims,
comprising a compensating module configured for attenuating the amplitude
of a received electromagnetic wave based on the distance traveled to said
10 surface by said electromagnetic wave, said compensating module being
configured for performing this attenuation on digital samples of the received
electromagnetic waves based on the distance and/or for performing this
attenuation by a command to turn on or off at least some of said radiating
elements determined based on said distance.
15
6. A flying device (20) comprising an embedded radar (10)
according to one of the preceding claims.
7. A processing method in a radar (10) embedded in a flying device
20 (20), the radar (10) comprising a transceiver antenna (11) including a plurality
of radiating elements (180) distributed over a surface (18) and configured for
the transmission and reception of an electromagnetic wave, said method
comprising the following steps:
- transmitting an electromagnetic wave from the antenna and receiving
25 an electromagnetic wave by the antenna;
wherein said method comprises the following step implemented by an
electronic gain control unit (12) of the radar:
- feedback controlling, through an adjustment loop, the antenna gain in
transmission and/or reception by turning on or off radiating elements of the
30 plurality of radiating elements, in order to keep the reception level of the
electromagnetic waves below a determined threshold below the saturation
zone of the radar.
18
8. The processing method in an embedded radar (10) according to
claim 7, wherein said adjustment loop comprises at least one of the steps
among steps a and b:
a/ determining the deviation between the current level of the received
5 electromagnetic wave and a reference level, determining the gain adjustment
as a function of said deviation and commanding the turning off or on of
radiating elements in transmission and/or reception based on said
determined gain adjustment;
b/ the transmission having taken place from a given height (h) relative
10 to a given surface (30) and at a given incidence angle (α), determining at
least one set of value(s) comprising at least one value among said given
height (h) and said given incidence angle (α), determining the gain
adjustment based on each value of said determined set of value(s) and
commanding the turning off or on of radiating elements in transmission
15 and/or reception based on said determined gain adjustment.
9. The processing method in an embedded radar (10) according to
claim 7 or 8, wherein said adjustment loop comprises adjusting the gain
according to a function calculating the gain value based on at least each
20 value of said set of value(s), said function being a decreasing function of said
value when the value is the height and an increasing function of the value
when the value is the incidence angle.
10. A computer program comprising software instructions which,
25 when executed by a computer, carry out a method according to any one of
claims 7 to 9.