Radio system with multiple antenna arrays and adaptive waveforms

Abstract

The radio system (10) comprises a waveform generator (1) alternately generating an FMCW wave representing a linearly frequency-modulated continuous wave for radar imaging and a CW wave representing a wave kept at a given frequency for measuring a velocity vector, an amplification chain (2), a set (4) of transmit antennas (41, 42, 43), a set (5) of receive antennas (51, 52, 531, 532), a set (7) of receivers (71-2, 731, 732), and a signal processor (9) implementing processing operations on FMCW signals received from the one or more lateral antennas (51, 52) of the set (5) of receive antennas (51, 52, 531, 532) and spectrally analysing CW signals received from the one or more lateral antennas (51, 52) and from the one or more ventral antennas (531, 532) of the set (5) of receive antennas (51, 52, 531, 532) so as to supply SAR images and components of the velocity vector of said airborne vehicle (20).

Description

[0001] TITLE: Radio system with multiple antenna arrays and adaptive waveforms.

[0002] TECHNICAL FIELD

[0003] The present invention relates to a radio system with multiple antenna arrays and adaptive waveforms, carried on a flying vehicle.

[0004] STATE OF THE ART

[0005] Small vehicles (or objects) designed to fly long distances (several tens of kilometers or more) must be able to navigate autonomously. Indeed, satellite navigation, such as GNSS (Global Navigation Satellite System), can be jammed ("GNSS-denied"), and carrying a sufficiently precise inertial navigation system (within a few meters) proves incompatible due to weight, size, and cost.

[0006] Autonomous navigation, in all weather and on all types of terrain, therefore requires an independent system which cannot be optical or infrared due to poor visibility in all weather conditions at ranges of several kilometers.

[0007] A radioelectric solution exploiting the reflectivity of the ground remains the only solution that can be sufficiently precise, lightweight and permanent.

[0008] Synthetic Aperture Radar (SAR) navigation appears suitable: navigational correction is performed by identifying ground features used as landmarks (roads, waterways, buildings, etc.). However, landmarks may be scarce or even absent along all or part of the flight path. This is particularly true over the sea, deserts, or large forests.

[0009] Furthermore, the speed of such small flying vehicles is poorly known. However, knowing the speed is essential for constructing the SAR image. Indeed, the adapted filtering that achieves azimuth resolution corresponds to a demodulation of a linearly frequency-modulated wave f over time t using the following formula F1: f = -2V 2 t / AR, well known to the man of the art, in which V is the velocity modulus (that is, the modulus of the velocity vector), l is the wavelength, and R is the observation distance.

[0010] Therefore, achieving a resolution of a few meters requires velocity accuracy on the order of 1%. Conventional SAR radars, designed for terrain analysis, have a velocity module derived from the aircraft's inertial navigation system or its satellite navigation system (and often a hybrid of both). When this velocity module is not precise enough, the image is blurry. A focusing process can be implemented: several suitable filters are applied, and the one with the best contrast on the ground image is selected. In this case, the initial inaccuracy is such that this process can be very cumbersome, but more importantly, it may not work if the contrast is too low (as in the case of a uniform ground surface).

[0011] It follows that, in order to address, on the one hand, the possible scarcity of landmarks, and on the other hand, the demand for speed accuracy necessary for good imaging, it is necessary to measure the velocity vector in conjunction with SAR imaging.

[0012] While the theory and development of a SAR radar are well known and described in the specialized literature, the measurement of the velocity vector is not the subject of equipment on the market.

[0013] The current situation is therefore not entirely satisfactory.

[0014] DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a radio-electric system mounted on a flying vehicle, which aims to overcome this drawback.

[0016] According to the invention, said radioelectric system comprises at least the following elements:

[0017] - a waveform generator generating, alternately, an FMCW wave (with "FMCW" for "Frequency Modulated Continuous Wave" in English) representing a continuous wave linearly modulated in frequency for radar imaging and a CW wave (with "CW" for "Continuous Wave" in English) representing a wave maintained at a given frequency for velocity vector measurement;

[0018] - an amplification chain switched to a set of transmitting antennas;

[0019] - the set of transmitting antennas comprising at least one lateral antenna and one ventral antenna; - a set of receiving antennas comprising at least one lateral antenna and one ventral antenna;

[0020] - a set of receivers connected to the set of receiving antennas; and

[0021] - a signal processor (or central processing unit) implementing FMCW signal processing received from the side antenna(s) of the receiving antenna array and spectral analysis of CW signals received from the side antenna(s) and ventral antenna(s) of the receiving antenna array in order to provide SAR images and velocity vector components of said flying vehicle.

[0022] Advantageously, said radioelectric system is configured to perform, from notable points in SAR images associated with a position prediction obtained from the velocity vector, a recalibration of the flying vehicle relative to the ground.

[0023] This radio system is therefore a radar-type system, mounted on a flying object (or carrier), which uses ground backscatter to extract velocity vector measurements and ground imagery. This system is specifically designed for flying object navigation, enabling it to autonomously determine its position relative to the ground, thus eliminating the need for GNSS satellite navigation or inertial navigation systems.

[0024] Advantageously:

[0025] - The transmitting antenna assembly comprises two lateral antennas oriented at approximately + / - 30° to the vertical of the flying vehicle, and the receiving antenna assembly comprises two lateral antennas oriented at + / - 30 0 approximately relative to the vertical to the flying vehicle; and / or

[0026] - the receiving antenna assembly includes a double ventral antenna, arranged vertically in relation to the flying vehicle.

[0027] In a preferred embodiment, the transmitting antenna array and the receiving antenna array are patch antenna arrays conforming to the shape of the flying vehicle. Furthermore, advantageously:

[0028] - the transmitting and receiving antenna arrays are decoupled and are associated by switching with the FMCW waveforms to perform SAR imaging and with the CW waveform for measuring the Doppler effect along the antenna axes;

[0029] - the ventral receiving antenna array is split into two sub-arrays forming two lobes so as to construct ε and D channels whose processing provides the incidence of the flying vehicle; and - the patch arrays exhibit a low sidelobe level pattern so as to resist jamming in threat directions.

[0030] Furthermore, and advantageously, the said radioelectric system is configured to operate sequentially according to the nature of the ground.

[0031] Furthermore, advantageously, said radio system is configured to operate in at least a part of the SHF (Special High Frequency) microwave range, and preferably in the C, X and Ku bands.

[0032] Moreover, advantageously, microwave transmit and receive modules are made using monolithic components or monolithic microwave MMIC integrated circuits in gallium arsenide (GaAs) or gallium nitride (GaN).

[0033] Furthermore, advantageously, the signal processor's processing algorithms are implemented on a programmable logic circuit of the FPGA type (for "Field-Programmable Gate Array" in English).

[0034] Furthermore, and advantageously, the said radioelectric system includes:

[0035] - a clock generator configured to synchronize at least the waveforms, digitization, and signal processing of the signal processor; and / or

[0036] - a microcontroller configured to perform at least some of the following functions: at least one configuration, at least one control and at least one supervision of elements of said system.

[0037] Therefore, the radio system, described above, is an on-board system, exploiting ground backscatter, which is measured in several directions using antenna arrays and by means of several waveforms which together allow the velocity vector of the flying vehicle to be measured and an image of the ground to be constructed.

[0038] This radioelectric system can, thanks to its antenna arrays and waveforms, provide right or left SAR images and the components of the velocity vector of the flying vehicle from which the notable points of the imagery associated with the position prediction obtained by the velocity vector allow the flying vehicle to be recalibrated relative to the ground.

[0039] This radio system thus provides a solution enabling navigational recalibration in all weather conditions, regardless of the type of ground. BRIEF DESCRIPTION OF THE FIGURES

[0040] Other features and advantages of the system according to the invention will become clearer from the following description of an example embodiment given by way of illustration and in no way limiting, annexed to the following figures.

[0041] Figure 1 is a block diagram of a particular embodiment of a radioelectric system.

[0042] Figure 2 is a block diagram of a waveform generator of the radio system.

[0043] Figure 3 is an example of waveform sequencing.

[0044] Figure 4 illustrates an example of the arrangement of transmitting antennas on a carrier.

[0045] Figure 5 shows an example of implementing transmitting antennas in the form of patch arrays.

[0046] Figure 6 illustrates an example of receiving antenna arrangement on a carrier.

[0047] Figure 7 shows an example of the implementation of receiving antennas in the form of patch arrays.

[0048] Figures 8A, 8B and 8C are different views illustrating an example of transmitting antenna arrangement on a carrier.

[0049] Figures 9A and 9B are different views illustrating an example of a receiving antenna arrangement on a carrier /

[0050] Figure 10 shows site and deposit openings of an nxm patch network.

[0051] Figure 11 is a front view of ventral antenna lobes.

[0052] Figure 12 is a lateral view of the ventral antenna lobes.

[0053] Figure 13 is a schematic representation showing the relative velocity and Doppler frequency on one of the antenna lobes.

[0054] DETAILED DESCRIPTION

[0055] The following description, given for illustrative purposes only and not as a limitation, concerns a radio system (hereinafter "system 10") mounted on a flying vehicle (or object), for example a small one, hereinafter referred to as "carrier 20". Said system 10 may correspond to an autonomous navigation radio system or to a navigation speed and imaging radar (NAVSAR).

[0056] The principle of the system 10 is based primarily on the design of antenna arrays whose beams are adapted, on the one hand, to the coverage of the terrain to be imaged, and on the other hand, to the measurement of the Doppler effect in various directions to extract the components of the velocity vector. Concurrently, the waveforms applied to the antenna beams are, on the one hand, an FMCW wave, namely a continuous wave linearly modulated in frequency (with "FMCW" for "Frequency Modulated Continuous Wave" in English), to form an image of the ground according to the known principle of a SAR (synthetic antenna radar), and on the other hand, a CW wave, namely a continuous wave (with "CW" for "Continuous Wave" in English) of constant amplitude and frequency, used to measure the Doppler effect of the relative velocity of the carrier 20 in the directions of the antenna beams.From this information, a navigation specialist is able to pinpoint the carrier's position relative to the ground.

[0057] As shown in Figure 1, the system 10 includes a waveform generator 1 (or synthesizer), an amplification chain 2, a switch 3, an array 4 of transmitting antennas, an array 5 of receiving antennas, a switch 6, a set 7 of receivers, a multiple analog-to-digital converter 8 (ADC), and a signal processor 9.

[0058] Waveform generator 1 (or synthesizer) provides, alternately, an FMCW wave and a CW wave at the desired frequency.

[0059] The choice of this frequency must be made from the C, X, Ku ranges, based on the following data:

[0060] - from the national regulator's frequency table;

[0061] - the available space on the carrier;

[0062] - of the range and accuracy on the velocity vector as required;

[0063] - the desired image resolution; and

[0064] - of the employment area (rain).

[0065] As an illustration, it should be noted that most aircraft SAR radars operate in the X-band (around 9.3 GHz). However, if the aircraft is small, it is advantageous to increase the frequency to allow for smaller antennas with the same directivity, while taking into account that rain can limit the range. Indeed, if the frequency is too high (for example, in the K-band around 20 GHz), the range is reduced to a few kilometers in rainy weather. Therefore, the parameters of the spectrum, power, and size of the antenna arrays (4 and 5) depend on the aircraft and its mission.

[0066] System 10 also includes a clock generator 11 and a microcontroller 12.

[0067] As shown in Figure 2, the waveform generator 1 (or synthesizer) includes a central synthesis component 13, a VCO-PLL (Voltage Control Oscillator - Phase Lock Loop), several of which are commercially available at the chosen frequencies. The waveform is driven by a sawtooth voltage generator 14, which controls the central synthesis component.

[0068] 13 in FMCW (sawtooth) or CW (direct current). The voltage generator

[0069] 14 sawtooth is itself driven by the clock generator 11 (preferably a commercial component) with regard to sequencing, illustrated in Figure 3, and by the microcontroller 12 with regard to parameters such as frequency and frequency excursion.

[0070] It should be noted that the frequency excursion (Af in Figure 3) determines the range resolution of the system 10 (SAR). The frequency stability of the system is ensured by a TCXO crystal 15 (a temperature-stable oscillator, many examples of which are commercially available), shown in Figure 2. Furthermore, as shown in Figure 3, the time-frequency sequencing is performed alternately in CW and then in FMCW. Typical values ​​for this timing are given as examples (t1 is, for example, between 10 and 20 seconds, and t2 is, for example, between 0.1 and 1 second), which is optimized according to the terrain overflown during the mission. Since navigation recalibration does not require continuous measurements of SAR (FMCW) and Doppler (CW) functions, this alternation saves a transmission and reception chain, as well as filtering to prevent interference. This allows for a compact and economical 10-system.

[0071] The amplification chain 2 may include a commercially available amplifier, the power of which, a few watts, depends on the desired range. It is followed by the switch 3, whose function is to direct the CW signal to a ventral antenna 43 and the FM / CW signal to one of the two lateral antennas 41 and 42 specified below, of the transmitting antenna array 4. The preferred embodiment with two lateral antennas 41 and 42 allows for the retrieval of the most relevant ground images relative to the ground track of the flight. This preferred embodiment is not mandatory, but it provides more possibilities for the system 10.

[0072] The set of transmitting antennas 41, 42, and 43 is shown in Figure 4. This set is implanted on the body 21 of the carrier 20. The ventral antenna 43 is oriented longitudinally along the X axis and perpendicular to the Z axis. X is the longitudinal axis of the carrier 21, Z is the vertical axis, and Y is the transverse axis (orthogonal to the X and Z axes). On either side of the ventral antenna 43 are the transmitting antennas 41 and 42, respectively on the left and right. Each of the antennas 41, 42 and 43 is formed of a network of patches 45 as shown in Figure 5. The aperture or directivity requirements are shown in Figure 10 and in vertical sections in Figures 11 and 12. According to Figure 12, the diagrams of the lateral antennas must cover on the ground the Y distance specified by the mission.

[0073] Figure 11 shows the L41, L42 and L43 lobes of the transmitting antennas 41, 42 and 43. The lobes of the receiving antennas are masked in this figure 11.

[0074] Figure 10 illustrates the elevation and azimuth beamwidths of an array of n xm patches. Figure 10 shows typical beamwidths for 45° and 55° patches spaced K / 2 apart. As an example, knowing that one degree covers 17m at 1000m, the elevation beamwidth (Os in Figure 10) to cover 1700m at 5000m requires a beamwidth of 20°. According to Figure 10, this would require 90 / 20, or approximately m = 5 patches. Regarding the azimuth beamwidth (0g in Figure 10) of all antenna arrays (beam perpendicular to the X-axis, Figure 12), the directivity or beamwidth must be as narrow as possible, both for the radar budget and the accuracy of Doppler measurements, and for controlling sidelobes. In this respect, one advantage of patch arrays is that the side lobes are phase-controlled by the distance between patches and their amplitude by the different sizes of the patches. This property allows, in particular, for better protection of the system against potential jammers.

[0075] The number of patches is optimized according to the carrier 20's ability to receive them. It should be noted that increasing the frequency allows for greater gain and directivity. However, a compromise must be made with rain attenuation, which becomes significant beyond the X band (9-10 GHz). The antenna parameters will be optimized according to the carrier 20 and its mission, as the system 10 has a wide range of applications. As an example, the array of transmitting antennas can be implemented on a single printed circuit board 46 soldered onto a pre-formed metal plate 47, as shown in Figures 8A, 8B, and 8C. This metal plate 47 is screwed onto the body 21 of the carrier 20 (using screws 48), with the three connectors 49A, 49B, and 49C (related to the three arrays) passing through the body 21 of the carrier 20.

[0076] The set 5 of receiving antennas 51, 52, 531 and 532 is shown in Figure 6. The set 5 is implanted on the body 21 of the carrier 20. The ventral antenna consists of two contiguous sub-arrays 531 and 532 longitudinally oriented in X and perpendicular to the -Z axis. The two sub-arrays 531 and 532 produce respectively a front lobe L531 and a rear lobe L532, as shown in Figure 12, which are separated by an angle e (Figures 12 and 13) from the perpendicular to the carrier, as shown in Figure 13. The sum of these two sub-arrays 531 and 532 provides a vertical sum lobe L53 (Figure 12), called å. By calculating the difference between lobes L531 and L532, a difference called D, an "amplitude monopulse" can be generated in the signal processor 9. This processing allows the direction of the vertical to the ground to be measured, that is, the angle α of incidence of the carrier 21, as shown in Figure 13.According to the "monopulse" theory, aa = arctangent(A / ε) (formula F2). Such a measurement is sometimes necessary to obtain the components of the velocity vector in the ground frame. Indeed, the antenna lobes measure Doppler effects, and therefore the relative velocities along the antenna axes in the carrier frame. It remains to project these values ​​onto the ground frame, using a standard mathematical operation performed by the signal processor.

[0077] Figure 12 shows the L532, L531 and L43 lobes of the ventral antennae 532, 531 and 43 as solid lines, and the L51, L52, L41 and L42 lobes of the lateral antennae 51, 52, 41 and 42 as dashed lines.

[0078] On either side of the ventral antenna 531, 532, the receiving antennas 51 and 52 are arranged, left and right respectively. The antenna diagrams follow the same criteria and considerations as those previously described for the transmitting antennas.

[0079] As an example, the same implementation as for transmission can be carried out, as shown in Figures 9A and 9B. Unlike the transmission arrays, the reception array has four connectors 59A, 59B, 59C, and 59D corresponding to the four antenna arrays (instead of three), since there are two ventral antenna sub-arrays instead of just one in transmission. More precisely, the array for the receiving antenna set 5 can be made on a single printed circuit board 56 soldered onto a pre-formed metal plate 57, as shown in Figures 9A and 9B. This metal plate 57 is screwed onto the body 21 of the carrier 20 (using screws 58), with the four connectors 59A, 59B, 59C, and 59D (related to the four arrays) passing through the body 21 of the carrier 20.

[0080] For optimal sensitivity, the transmitting and receiving antenna arrays must be sufficiently separated to ensure adequate decoupling. Furthermore, low-noise amplifiers (LNAs), or even bandpass filters if required by the radio environment, are used as close as possible to the antenna output connectors.

[0081] Each antenna output (filtered, amplified) is, as shown in Figure 2, directed to one of the receivers 71-2, 731, or 732 of assembly 7 shown in Figure 2. The outputs of the lateral antennas 51 and 52 are switched by switch 6 to receiver 71-2 depending on the imaging (right or left) to be performed. The outputs of the ventral antennas 531 and 532 are connected to receivers 731 and 732. The receivers function to transpose the microwave signal into an amplified and filtered intermediate frequency (Fl) so that it can be digitized and processed in the signal processor 9. These reception chains, in these frequency ranges, are well known. They consist of a low noise amplifier (LNA), a mixer (preferably l / Q, in phase and in quadrature), the local oscillator of this mixer coming from the synthesizer (or waveform generator 1).The mixer is followed by a low-pass filter and one or more amplifiers. These various components are commercially available.

[0082] As shown in Figure 1, the outputs of the receiver array 7 are digitized by the analog-to-digital encoders (ADCs) 8, whose sampling rate is more than 2.5 times the intermediate frequency (Shannon's Theorem) and whose dynamic range encompasses that of the ground reflectivity (approximately 30 dB) and that of the radar budget as a function of range (approximately 30 dB). The sampling rate is set by the clock generator 11. As an example, an AD9653 Quad ADC, 16-bit, 125 Msps, is suitable for many configurations because of its wide dynamic range. It also has the advantage, for compact systems, of encoding four channels in parallel with a single component. Other ADCs with equivalent or superior performance can be used.

[0083] The digitized signals are then injected into the signal processor 9.

[0084] Two types of processing (sequence of algorithms) are applied and programmed in the signal processor 9, depending on the waveform used.

[0085] During FMCW transmission (Figure 3), the signal processor 9 performs a standard SAR processing procedure. The signal processor 9 extracts a ground image composed of pixels with intensities dependent on ground reflectivity and a resolution on the order of one or a few meters. The image size is approximately 2 km x 2 km. Its dimensions depend on the transmission period, the platform altitude, and the elevation range of the lateral antenna. This image allows the system 10 to locate the alignment markers.

[0086] During CW transmission, the signal processor 9 performs a spectral analysis on each of the receiving antennas. The average Doppler effects on each antenna lobe L (Figure 13) are determined by the formula F3: fd = -2Vr / A, where λ is the wavelength and Vr is the projection of the velocity vector onto the antenna axis. The Vr projections correspond to the relative velocities of the carrier 20 with respect to the ground S, in each direction along the axis of these antennas.

[0087] The magnitude V of the velocity (Figure 13) corresponds to the formula F4: V=fd * A / 2sin(a+s) where fd is the measured Doppler frequency, A is the wavelength, a is the incidence (angle between the axis of carrier 21 and the velocity vector), and e is the pointing error of the axis of the antenna considered with the carrier 21.

[0088] According to formula F4 and spectral analysis providing fd (Doppler frequency), the velocity magnitude and the carrier's incidence angle with its trajectory are obtained. Formula F3 provides as many relative velocities as there are antennas, thus allowing the velocity vector to be reconstructed from its components along the antenna axes. Spectral analysis can be performed using a Fast Fourier Transform (FFT) algorithm, a function commonly programmed on FPGAs. The accuracy obtained for each component is proportional to the width of the spectrum obtained by the FFT transformation. The narrower the antenna lobe, the less spread the spectrum, and the more accurate the velocity measurement will be. Figure 13 illustrates the deviation of a lobe according to the carrier's incidence angle and its associated Doppler frequency. Parameters for optimizing the accuracy performance of system 10 are indicated below.According to estimation theory, the optimal standard deviation ofd of the Doppler measurement follows the formula F5: ofd = k0 / V²S / B, where S / B is the signal-to-noise ratio, Q is the antenna lobe width, and k = 2Vr / A. The accuracy of the V measurement therefore depends on the available longitudinal space on the carrier, which allows for refining Q, the choice of frequency, the radar budget, and the estimator of the Doppler spectrum center. These parameters are chosen based on the carrier and its mission, as well as the constraints imposed by the carrier (size, power, consumption, price).

[0089] The implementation of algorithms is preferably carried out on FPGA-type programmable logic circuits (Field-Programmable Gate Array). A wide range of FPGA circuits are available on the market. The choice of FPGA type by the signal specialist is made according to their familiarity with the implemented functions and the programming tools of the FPGA manufacturer.

[0090] As shown in Figure 1, the system 10 is configured and monitored by the microcontroller 12, preferably a commercially available one. The configuration consists of setting the optimal parameters for the carrier's mission. Thus, the microcontroller 12 sets the waveform sequence shown in Figure 3, the durations of the FMCW and CW modes, the CW frequencies, and the Af frequency excursions of the FMCW mode. To this end, commands are sent to the clock generator 11, which provides the FMCW and CW mode sequencing, and in parallel to the voltage generator 14 (Figure 2), which provides the VCO-PLL component 13 with either a sawtooth voltage or a DC voltage, respectively. The clock generator 11 (preferably a commercially available one) also provides the control times for the switches synchronously with the waveform mode sequence. The clock generator 11 also controls the sampling rate of the converter 8 and the signal processor 9.

[0091] The microcontroller 12 also monitors the system 10, particularly before the mission and after configuration. This monitoring involves verifying that the system 10 is functioning according to its programming. To this end, the microcontroller 12 initiates transmission sequences and monitors the operation of the various subsystems (levels and rates). For example, coupling is applied between the transmitting and receiving antennas, and the responses of the signal processor 9 are tested. Other test procedures may be applied. Finally, the microcontroller 12 verifies the communication between the signal processor 9 and the carrier's navigation system.

[0092] The said system 10, which exploits ground backscatter to extract ground imagery and velocity vectors for the purpose of performing all-weather and all-terrain navigation recalibration, can represent an autonomous radio navigation system.

[0093] System 10, as described above, therefore has many advantages.

[0094] Firstly, in the absence of the possibility of navigation by satellite navigation systems (type GNSS), the system 10 allows positioning of the carrier relative to the ground flown over with an accuracy of a few meters.

[0095] Compared to a high-performance inertial navigation system, the System 10 is more precise, much lighter, and much less expensive. Indeed, an inertial navigation system equipping a transoceanic airliner is typically affected by a drift in its position estimation on the order of NM / h (nautical miles per hour). The cost of such an inertial navigation system can run into hundreds of thousands of euros; a System 10 is an order of magnitude less expensive.

[0096] Furthermore, system 10 offers other advantages, including the following:

[0097] - precision: the combination of SAR imaging and velocity vector allows for ground positioning accuracy on the order of a few meters;

[0098] - availability: the system 10 allows all-weather navigation and works regardless of the terrain or sea and its condition;

[0099] - Flexibility depending on the mission: the time-frequency sequence is adaptable according to the (pre-programmed) route of the carrier. Over the sea or the desert, for example, it will be in CW mode, while over ground containing information, it will switch to the more precise FMCW mode;

[0100] - compactness: the simplicity of the electronics allows integration into a few liters and the patch antennas are a few millimeters thick on the body of the carrier, not altering its aerodynamics;

[0101] - Consumption: the good radar balances obtained through continuous emissions, antenna gain and integration times require only a few watts of transmission. The use of the latest monolithic microwave MMICs (for "Microwave Monolithic Integrated Circuits" in English) in gallium nitride GaN (for "Gallium Nitride" in English) provides an efficiency of 20 to 30%;

[0102] - Anti-interference: Protection against interference is ensured primarily by the spectral spreading visible in Figure 3 and jointly by the directivity of the antennas. Indeed, an advantage of patch arrays is that the side lobes are controlled in phase by the distance between patches and the amplitude by the size of the patches;

[0103] - Existing technology on the market: all the components mentioned in the detailed description exist in the frequencies where the system 10 can be applied; - Reliability: it is well known that the mean time between failures MTBF (for "Mean Time Between Failures")

[0104] The Time Between Failures (TBF) of MMIC circuits is very high;

[0105] - diversity of applications.

Claims

DEMANDS 1. Radio system, said radio system (10) being carried on a flying vehicle (20), characterized in that it comprises at least the following elements: - a waveform generator (1) generating, alternately, an FMCW wave representing a continuous wave linearly modulated in frequency for radar imaging and a CW wave representing a wave maintained at a given frequency for velocity vector measurement; - an amplification chain (2) switched to a set (4) of transmitting antennas (41, 42, 43); - the set (4) of transmitting antennas (41, 42, 43) comprising at least one lateral antenna (41, 42) and one ventral antenna (43); - a set (5) of receiving antennas (51, 52, 531, 532) comprising at least one lateral antenna (51, 52) and one ventral antenna (531, 532); - a set (7) of receivers (71-2, 731, 732) connected to the set (5) of receiving antennas (51, 52, 531, 532); and - a signal processor (9) implementing FMCW signal processing received from the lateral antenna(s) (51, 52) of the receiving antenna assembly (5) (51, 52, 531, 532) and spectral analysis of CW signals received from the lateral antenna(s) (51, 52) and ventral antenna(s) (531, 532) of the receiving antenna assembly (5) (51, 52, 531, 532) so as to provide SAR images and velocity vector components of said flying vehicle (20).

2. System according to claim 1, characterized in that the assembly (4) of transmitting antennas comprises two lateral antennas (41, 42) oriented at + / -30 0 approximately with respect to the vertical (Z) to the flying vehicle (20) and in that the receiving antenna assembly (5) comprises two lateral antennas (51, 52) oriented at + / -30 0approximately relative to the vertical (Z) to the flying vehicle (20).

3. System according to any one of claims 1 and 2, characterized in that the set (5) of receiving antennas comprises a double ventral antenna (531, 532), arranged vertically with respect to the flying vehicle (20).

4. System according to any one of claims 1 to 3, characterized in that the set (4) of transmitting antennas and the set (5) of receiving antennas are patch antenna arrays (45, 55) conforming to the shape of the flying vehicle (20).

5. System according to claim 4, characterized in that the transmitting and receiving antenna arrays are decoupled and are associated by switching to the FMCW waveforms to perform SAR imaging and to the CW waveform for measuring the Doppler effect along the antenna axes.

6. System according to any one of claims 4 and 5, characterized in that the ventral receiving antenna array is split into two sub-arrays (531, 532) forming two lobes (L531, L532) so as to construct channels å and D whose processing provides the incidence (a) of the flying vehicle (20).

7. System according to any one of claims 4 to 6, characterized in that the patch networks exhibit a low sidelobe level diagram so as to resist jamming in threat directions.

8. System according to any one of the preceding claims, characterized in that it is configured to operate sequentially according to the nature of the soil.

9. System according to any one of the preceding claims, characterized in that it is configured to operate in at least a part of the SHF microwave range.

10. System according to claim 9, characterized in that it is configured to operate in the C, X and Ku bands.

11. System according to any one of claims 9 and 10, characterized in that the microwave transmit and receive modules are made using monolithic components or monolithic microwave MMIC integrated circuits in gallium arsenide or gallium nitride.

12. System according to any one of the preceding claims, characterized in that the signal processor (9) processing algorithms are implemented on an FPGA type programmable logic circuit.

13. System according to any one of the preceding claims, characterized in that it includes a clock generator (11) configured to synchronize at least the waveforms, digitization and signal processing of the signal processor (9).

14. System according to any one of the preceding claims, characterized in that it comprises a microcontroller (12) configured to perform at least some of the following functions: at least one configuration, at least one control and at least one supervision of elements of said system (10).

15. System according to any one of the preceding claims, characterized in that it is configured to perform, from notable points of the SAR images associated with a position prediction obtained from the velocity vector, a recalibration of the flying vehicle (20) with respect to the ground (S).

Images