IFF / ADS-B RECEIVING CHAIN

Abstract

The invention relates to a receiving chain (100) for receiving IFF and ADS-B signals while rejecting at least one intermediate frequency band, comprising: - a receiving antenna (101), - an analog section (102) with: o a dual-band filtering device (103) passing around the frequency bands of the IFF and ADS-B signals while rejecting the intermediate frequency band, o a low-noise amplifier (104), o a mixer (106) configured to transpose the IFF and ADS-B signals to lower frequencies, o an analog-to-digital converter (109), - a digital section (110) configured to duplicate the digitized signal (112), and to process the duplicated signals respectively on a first IFF path (120) and a second ADS-B path (130), each comprising a filtering device (121 / 131), a frequency transposition device (122 / 132), and means of signal processing (124 / 134).

Description

Technical field:

[0001] The invention relates to the field of air traffic control and anti-collision devices. It relates more specifically to a reception chain configured to allow the simultaneous reception of IFF interrogations (English acronym for Identification Friend of Foe, or identification friend enemy) and ADS-B interrogations (English acronym for Automatic Dependent Surveillance-Broadcast) , while ensuring strong constraints on the rejection of third-party signals. Previous technique:

[0002] IFF is an encrypted aircraft identification system that allows civilian or military approach radars to recognize cooperating, so-called "friendly" aircraft and determine their heading and distance. IFF is also used in flight in military aircraft to identify friendly and enemy aircraft. IFF interrogations are made by ground stations or aircraft on a frequency band centered around 1030 MHz, typically 14 MHz.

[0003] ADS-B is a cooperative surveillance system for air traffic control. An aircraft equipped with ADS-B determines its position using a global positioning satellite system (GNSS). Global Navigation Satellite System ) and sends it periodically to ground stations and other aircraft flying nearby. The position transmission rate depends on the phase of flight. ADS-B transmissions are made on a frequency band centered around 1090 MHz, typically 16 MHz.

[0004] Most aircraft, especially airplanes, carry the equipment necessary to implement these two standards, in particular the equipment necessary to listen to IFF on the 1030 MHz frequency and ADS-B on the 1090 MHz frequency.

[0005] These receiving equipments are subject to strong performance constraints by the standards DO-260 B or C (for ADS-B), AIMS 03-1000 (for IFF), and ED73 E or F (ADS-B). The constraints relate in particular to minimum rejection levels for the receiving radio channels. In particular, the rejection levels to be achieved are very high (greater than 60 dB) on the 1053 MHz - 1065 MHz band which is located between the IFF reception frequency and that of ADS-B.

[0006] In order to meet these strong rejection constraints, state-of-the-art aircraft generally carry separate equipment for IFF and ADS-B. This equipment has head-end analog filters designed to achieve the rejection levels defined by the standards, by cascading a large number of bandpass filters of various technologies (ceramic cavities, SAW filters (English acronym for Surface Acoustic Waves, or surface wave filter), BAW filters (English acronym for Bulk Acoustic Wave , or bulk wave filter), etc.).

[0007] Some devices, such as Thales' TSC4000, receive IFF interrogations and ADS-B messages in the same device. However, these receptions are done on two separate radio channels.

[0008] Carrying two separate receiving devices or two separate receiving chains in an aircraft to perform IFF reception and ADS-B reception functions has obvious consequences in terms of volume and weight, which may not be compatible with small aircraft. In addition, the consumption of the equipment is not optimal, which is a major drawback for drone-type applications. Finally, the components of each receiving chain are relatively expensive, and the higher their number, the higher the serial cost.

[0009] An aim of the invention is therefore to describe equipment having a single reception chain making it possible to continuously receive IFF interrogations around the frequency 1030 MHz and ADS-B transmissions around the frequency 1090 MHz, while respecting the normative constraints associated with these receptions. Summary of the invention:

[0010] To this end, the present invention describes a reception chain configured to allow the reception of IFF signals received in a frequency band centered on the frequency 1030 MHz and of ADS-B signals received in a frequency band centered on the frequency 1090 MHz, and to reject at least one frequency band between the frequency 1030 MHz and the frequency 1090 MHz. The reception chain according to the invention comprises: a receiving antenna configured to receive a radio frequency signal in a frequency band comprising the frequencies 1030 MHz and 1090 MHz, an analog part with: ∘ a dual-band filtering device configured to filter the radio frequency signal acquired on the receiving antenna by passing around the frequency bands of the IFF and ADS-B signals while rejecting said frequency band between the frequency 1030 MHz and the frequency 1090 MHz, ∘ a low-noise amplifier configured to amplify the radio frequency signal filtered by said dual-band filtering device, ∘ a mixer configured to mix the signal amplified by the low-noise amplifier with a sinusoidal signal so as to transpose the signals received on the frequency bands of the IFF and ADS-B signals to lower frequency bands, ∘ an analog-to-digital converter configured to digitize the signals received on said lower frequency bands.

[0011] It also includes a digital part configured to duplicate the digitized signal, and to process the duplicated signals respectively on: a first path comprising a first filtering device and a first frequency transposition device, configured to filter and transpose to a working frequency the signals received around the frequency bands corresponding to the IFF signals transposed by said mixer, and further comprising means for processing the IFF signals, a second path comprising a second filtering device and a second frequency transposition device, configured to filter and transpose to a working frequency the signals received around the frequency bands corresponding to the ADS-B signals transposed by said mixer, and further comprising means for processing the ADS-B signals.

[0012] According to one embodiment of the reception chain according to the invention, the dual-band filtering device is a dual-band filter.

[0013] According to one embodiment of the reception chain according to the invention, the dual-band filtering device is configured to reject by at least 30dB the signals received in said frequency band between the frequency 1030 MHz and the frequency 1090 MHz.

[0014] Advantageously, the dual-band filtering device, the first filtering device and the second filtering device are configured to together reject by at least 60 dB signals received outside the reception frequency bands of the IFF and ADS-B signals.

[0015] According to one embodiment of the reception chain according to the invention, the frequency band between the frequency 1030 MHz and the frequency 1090 MHz comprises the frequency band 1053 MHz - 1065 MHz.

[0016] According to one embodiment of the reception chain according to the invention, the sinusoidal signal used by the mixer to mix the signal amplified by the low noise amplifier is a sinusoidal signal whose frequency is substantially equal to 1050 MHz or 1070 MHz.

[0017] According to one embodiment, the reception chain according to the invention further comprises one or more bandpass or lowpass filters configured to reject intermodulation lines generated by at least one of the mixer, the first frequency transposition device and the second frequency transposition device.

[0018] According to one embodiment, the reception chain according to the invention further comprises means for oversampling and adjusting the power level of the signals digitized by the analog-digital converter. Brief description of the figures:

[0019] The invention will be better understood and other characteristics, details and advantages will appear more clearly on reading the following description, given without limitation, and thanks to the appended figures, given by way of example, among which: there figure 1 represents a functional block diagram of a reception chain 100 according to an embodiment of the invention. figure 2 gives an example of a dual-band analog filter template that can be used for implementing a receiver according to an embodiment of the invention. Detailed description:

[0020] There are several ways to implement an IFF or ADS-B reception chain. In all cases, the radio signal, whether centered around the 1030 MHz or 1090 MHz frequency, is filtered and then amplified using a low-noise amplifier, then filtered again, the filters being necessary to meet the rejection constraints of the DO-260, AIMS 03-1000 and ED73 standards. The signal is then either directly digitized or converted into a video signal and then digitized.

[0021] Receivers can be heterodyne or homodyne, and the signal digitization is done at low intermediate frequency, either directly on the radio signal or on a video signal produced from the radio signal.

[0022] The historical solution consists of heterodyne reception of the signal, converting it into a video signal at a low intermediate frequency, and then digitizing the video signal. Converting the signal into a video signal consists of working only on the logarithmic envelope of the signal. The advantage of this solution is that it is low cost and requires little processing, which is why it is still a solution used, despite its size.

[0023] Another solution is to directly digitize IFF or ADS-B signals on their carrier frequency, using very powerful and high-performance CANs. However, this solution is expensive to implement, and CANs are considered critical complex components that must meet certification constraints specific to aeronautics (DO-284 standard), which is why it is not widely used in aero components.

[0024] More recent solutions consist of digitizing the entire received radio signal in the form of I / Q signals. These solutions, whether from heterodyne or homodyne reception, allow for more powerful digital processing since there is no loss of information linked to the conversion of the signal into a video signal.

[0025] Designing a radio chain allowing the simultaneous reception of IFF and ADS-B signals, with stable filtering in the frequency bands of interest and respecting the normative constraints on signal rejection levels outside these bands, proves to be particularly difficult. Indeed, while it is possible to design analog filters allowing the desired rejection levels to be achieved around one or the other of the IFF or ADS-B frequency bands, designing analog filters that are simultaneously passable and stable around the two frequencies of interest while guaranteeing the required rejection levels (greater than 60dB) outside these bands, and in particular in the intermediate frequency band, requires the use of particularly high-order filters. Such filters are particularly complex and expensive to produce, present in-band ripple problems, and have significant weight and volume.

[0026] The realization of a high-order digital filter that is stable and passable on both frequency bands of interest and has the desired rejection properties is theoretically possible. However, such a filter would be positioned in the reception chain after the ADC (Analog-to-Digital Converter), which consequently would not be protected against high-level emissions occurring in frequency bands close to those of IFF and ADS-B, in particular those received in the frequency band located between the two bands of interest. These unrejected emissions can have the effect of making the ADC work at saturation. In practice, saturation of the ADC leads to non-linear distortion that at least creates broadband spectral noise, which destroys the receiver's dynamics, and at worst will lead to its deterioration.

[0027] In order to overcome the shortcomings of the state of the art, and taking into account the constraints presented above, the invention defines a hybrid analog-digital radio reception chain having: a first level of dual-band analog filtering, intended to provide part of the desired rejection of signals located outside the bands of interest, in particular those received between the IFF signal and the ADS-B signal, in order to avoid saturation of the CAN linked to non-essential radiation, then a second level of digital filtering, adapted to one or other of the signals of interest, configured so that the two levels of filtering together make it possible to achieve the normative requirements.

[0028] There figure 1 represents a functional block diagram of a reception chain 100 according to an embodiment of the invention, allowing the simultaneous reception of IFF (1030 MH) and ADS-B (1090 MHz) signals.

[0029] It comprises a receiving antenna 101, configured to receive a radio frequency signal in a frequency band comprising IFF and ADS-B signals, i.e. the frequencies 1030 MHz and 1090 MHz.

[0030] It then includes an analog part 102 configured to provide head processing to the received signals, until their digitization.

[0031] In this respect, the analog part 102 of the radio chain 100 according to one embodiment of the invention comprises a dual-band filtering device 103 configured to filter the radiofrequency signal acquired on the receiving antenna 101, passing around the frequency bands of the IFF signals (centered around 1030 MHz) and ADS-B signals (centered around 1090 MHz) and rejecting the signals outside these bands, in particular those located in the intermediate frequency band.

[0032] According to one embodiment of the invention, the dual-band filtering device 103 may comprise one or more cascaded analog band-pass filters, intended to filter the signal around the IFF frequency band (1030 MHz), and around the ADS-B frequency band (1090 MHz).

[0033] According to another embodiment, the dual-band filtering device 103 can be produced by a diplexer (neologism from the English diplex ) splitting the signal into two channels, each channel being filtered using a bandpass filter designed to filter signals around the IFF (1030 MHz) and ADS-B (1090 MHz) frequency bands, for example the BAW filters 880367 and 880374 from QORVO. The two channels are then recombined using a combiner (in English combine). The diplexer and the combiner are designed to ensure the correct adaptation of each channel to the other at the two frequencies of interest IFF (1030 MHz) and ADS-B (1090 MHz), for example, using quarter-wave lines, loaded or not.

[0034] According to another embodiment of the invention, more advantageous because it is more compact and simpler to produce, the dual-band filtering device 103 can take the form of a dual-band analog radio filter. This analog filter contributes to the rejection of signals outside the IFF and ADS-B bands, but is not bound by the constraints defined by the standards, which is why its size can be more relaxed, thus making the production of such an analog filter possible.

[0035] There figure 2 gives an example of a dual-band analog filter template 103 that can be used for implementing a receiver according to an embodiment of the invention.

[0036] This filter is defined as passing between the frequencies f Q1 = 1005 MHz and f Q2 = 1055 MHz, i.e. in the frequency band associated with the reception of IFF signals. The oscillation of the signals in the sub-band f Q01 = 1016 MHz to f Q01 = 1044 MHz is limited to 6 dB, so as to minimize distortions of the IFF signal.

[0037] This filter is also defined as passing between the frequencies f A1 = 1065 MHz and f A2 = 1115 MHz, i.e. in the frequency band associated with the reception of ADS-B signals. The oscillation of the signals in the sub-band f Q01 = 1076 MHz to f Q01 = 1104 MHz is limited to 6 dB, so as to minimize distortions of the ADS-B signal.

[0038] Outside these two frequency bands, the filter rejection level is greater than 30 dB, particularly in the 1055 MHz - 1063 MHz frequency band, which ensures sufficient rejection to avoid the phenomenon of CAN saturation by signals transmitted in this frequency band.

[0039] The analog part 102 of the radio chain 100 according to one embodiment of the invention also comprises a low-noise amplifier 104 configured to amplify the radiofrequency signal filtered by the dual-band filtering device 103. Advantageously, the amplifier can be followed by a bandpass filter 105 configured to reject signals far from the frequency bands of interest. In the example of the figure 1 , the bandpass filter 105 passes over a fairly wide frequency band ranging from 900 MHz to 2 GHz.

[0040] The analog part 102 of the radio chain 100 according to one embodiment of the invention then comprises a mixer 106 configured to mix the signal amplified by the low noise amplifier (and possibly filtered by the filter 105) with a sinusoidal signal 107, so as to transpose the signals received on the frequency bands of the IFF and ADS-B signals to lower frequency bands that can be digitized by the analog-digital converter. Such a mixer is characteristic of a heterodyne receiver. The frequency of the sinusoidal signal 107 is chosen so as to avoid the phenomena of interlacing of the IFF and ADS-B intermodulation lines.

[0041] An advantageous frequency for the sinusoidal signal is a frequency close to 1050 MHz, which allows the IFF signal to be transposed to the 20 MHz frequency and the ADS-B signal to the 40 MHz frequency while avoiding intermodulation lines appearing in the frequency bands of interest.

[0042] Another advantageous frequency for the sinusoidal signal is a frequency close to 1070 MHz, which allows the IFF signal to be transposed to the 40 MHz frequency and the ADS-B signal to the 20 MHz frequency while avoiding intermodulation lines appearing in the frequency bands of interest.

[0043] Other frequencies are possible, with the exception of frequencies close to 1060 MHz which would cause intermodulation lines of the IFF signal to appear in the frequency band of the ADS-B signal and vice versa. In particular, the frequency can be lower than 1030 MHz, or higher than 1090 MHz, as long as the frequencies to which the signals of interest are transposed are compatible with the ADC.

[0044] According to an advantageous embodiment of a reception chain 100 according to the invention, the transposition of the signals is followed by a filtering 108 whose purpose is to eliminate intermodulation lines resulting from the frequency transposition, such as, for example, in the case of a transposition with a sinusoidal signal at 1050 MHz, a low-pass filter having a cut-off frequency of 70 MHz.

[0045] Finally, the analog part 102 of the radio chain 100 according to one embodiment of the invention comprises an analog-to-digital converter (ADC) 109 configured to digitize the transposed IFF and ADS-B signals. The sampling rate of the ADC is chosen to be at least twice the highest frequency of the transposed signals, so as to comply with Shannon's theorem. The ADC is chosen so that its noise figure is compatible with the expected reception performance.

[0046] The reception chain 100 also comprises a digital part 110 configured to provide the additional filtering necessary to meet the regulatory constraints, and to process the IFF and ADS-B signals. This digital part can be implemented on computing means such as for example a microprocessor, a DSP (English acronym for Digital Signal Processor , or digital signal processor), an FPGA (English acronym for Field Programmable Gate Array , or programmable gate array), an ASIC (English acronym for Application-Specific Integrated Circuit , or integrated circuit specific to an application), any combination of these means, or any hardware component allowing the processing of the digital part 110 described below to be carried out.

[0047] According to an advantageous embodiment of the invention, the digital part 110 is configured to implement optional processing operations 111 for oversampling and adjusting the power of the received signals. The oversampling of the received signals makes it possible to reduce the sampling rate of the CAN 109, and thus to reduce its consumption. The adjustment of the power of the signals makes it possible to position their dynamics as best as possible in order to carry out subsequent processing operations in optimal arrangements. Alternatively, the oversampling can be carried out later in the digital part.

[0048] The digital part 110 is further configured to carry out a duplication 112 of the signals, and to process them according to two separate paths: a first path 120, where processing is implemented to allow the interpretation of the IFF signals, a second path 130, where processing is implemented to allow the interpretation of the ADS-B signals.

[0049] Duplication 112 consists of a copy of the digitized signals (and possibly oversampled and power adjusted).

[0050] Each of the paths includes a filtering device 121 / 131 and a frequency transposition device 122 / 132.

[0051] The filtering devices 121 / 131 are configured to filter the signal around the transposed frequency of interest (the frequency 20 MHz for the path 120 associated with the IFF signal and the frequency 40 MHz for the path 130 associated with the ADS-B signal in the case of a mixture 106 with a sinusoidal signal 107 at the frequency 1050 MHz). These filtering operations are complementary to those carried out by the analog filter 103, and are defined so that these filters together provide the rejection levels defined by the standards DO-260, AIMS 03-1000 and ED73. They may be different on the IFF path 120 and on the ADS-B path 130, and are adapted to the spectral template of the signals processed on each path. In particular, they ensure, in addition to the dual-band head filter 103, a rejection greater than 60 dB of the signals received in the frequency band 1053 MHz - 1065 MHz.

[0052] In the case of a mixture 106 with a sinusoidal signal 107 at the frequency 1050 MHz, the filter 121 may be, for example, a low-pass filter rejecting by more than 30 dB the signals located above the frequency 25 MHz. Similarly, in the same application case, the filter 131 may be, for example, a band-pass filter rejecting by more than 30 dB the signals located outside a frequency band of 50 MHz centered on the frequency 40 MHz.

[0053] The frequency transposition devices 122 / 132 are configured to transpose the signals to working frequencies, i.e. operating frequencies enabling subsequent signal analysis processing to be carried out. For example, in the case of a mixture 106 with a sinusoidal signal at the frequency 1050 MHz, the carrier frequency of the signals for the path 120 associated with the IFF signal is 20 MHz and 40 MHz for the path 130 associated with the ADS-B signal. The frequency transposition device can then take the form of an I / Q demodulator, configured to transpose the signals to the baseband and convert them into IQ samples. Alternatively, the frequency transposition device can be a mixer configured to transpose the signals to a carrier frequency suitable for processing the IFF or ADS-B signals. The working frequencies of the IFF signal and the ADS-B signal are not necessarily identical.Advantageously, the frequency transposition devices 122 and 132 can be followed by a low-pass filter 123 / 133 configured to eliminate intermodulation lines linked to the transposition of the signals.

[0054] On each path, the positions of the filter device 121 / 131 and the frequency transposition device 122 / 132 may be reversed. In the case of baseband transposition, the filter devices 121 / 131 may be low-pass filters. However, the arrangement shown in figure 1 is advantageous since it avoids the appearance of intermodulation lines linked to the presence of the ADS-B signal on path 120 of the IFF signal and vice versa.

[0055] Finally, each path includes means 124 / 134 for processing the demodulated samples. These processes are not described here in detail because they correspond to the known state-of-the-art processes allowing the decoding of IFF or ADS-B signals, namely the calculation of intercorrelation products, the conversion of the signals into video signals, and the search for pulses in these signals.

[0056] The reception chain according to the invention therefore makes it possible to receive IFF signals and ADS-B signals in a combined manner in a compact solution. It has an analog part and a digital part, configured to together achieve the rejection performances defined by the DO-260 B and C, AIMS 03-1000 and ED73 E and F standards. It differs from state-of-the-art reception chains in that the rejection is provided by both: an analog filter located at the processing head, intended to protect the CAN from signals which could have the effect of saturating it, in particular signals transmitted in the frequency band located between the frequency band of IFF signals and the frequency band of ADS-B signals, digital filters located after the CAN, intended to provide the additional filtering required to enable IFF and ADS-B reception.

[0057] It brings: better reception management, thanks to the transfer of filtering and demodulation functions to the digital part. Indeed, digital processing is more stable, and it is easier to adjust digital processing than hardware components, and a reduction of at least two in the surface area of ​​IFF and ADS-B reception functions, the number of components, the weight, the consumption and the number of antennas, which is critical for small aircraft and allows for cost reduction.

Claims

1. Reception chain (100) configured to allow the reception of IFF signals received in a frequency band centered on the frequency 1030 MHz and of ADS-B signals received in a frequency band centered on the frequency 1090 MHz, and to reject at least one frequency band between the frequency 1030 MHz and the frequency 1090 MHz, characterized in that it comprises: - a reception antenna (101) configured to receive a radiofrequency signal in a frequency band comprising the frequencies 1030 MHz and 1090 MHz, - an analog part (102) with: ∘ a dual-band filtering device (103) configured to filter the radiofrequency signal acquired on the reception antenna by passing around the frequency bands of the IFF and ADS-B signals while rejecting said frequency band between the frequency 1030 MHz and the frequency 1090 MHz,∘ a low noise amplifier (104) configured to amplify the radio frequency signal filtered by said dual-band filtering device, ∘ a mixer (106) configured to mix the signal amplified by the low noise amplifier with a sinusoidal signal (107) so as to transpose the signals received on the frequency bands of the IFF and ADS-B signals to lower frequency bands, ∘ an analog-to-digital converter (109) configured to digitize the signals received on said lower frequency bands, - a digital part (110) configured to duplicate the digitized signal (112) and to process the duplicated signals respectively on: ∘ a first path (120) comprising a first filtering device (121) and a first frequency transposition device (122), configured to filter and transpose to a working frequency the signals received around the frequency bands corresponding to the transposed IFF signals by said mixer,and further comprising means for processing (124) the IFF signals, ∘ a second path (130) comprising a second filtering device (131) and a second frequency transposition device (132), configured to filter and transpose to a working frequency the signals received around the frequency bands corresponding to the ADS-B signals transposed by said mixer, and further comprising means for processing (134) the ADS-B signals., 2. Reception chain according to claim 1, wherein said dual-band filtering device (103) is a dual-band filter.

3. Reception chain according to one of the preceding claims, in which the dual-band filtering device (103) is configured to reject by at least 30dB the signals received in said frequency band between the frequency 1030 MHz and the frequency 1090 MHz.

4. Reception chain according to one of the preceding claims, in which the dual-band filtering device (103), the first filtering device (121) and the second filtering device (131) are configured to together reject by at least 60 dB signals received outside the reception frequency bands of the IFF and ADS-B signals.

5. Reception chain according to one of the preceding claims, in which said frequency band between the frequency 1030 MHz and the frequency 1090 MHz comprises the frequency band 1053 MHz - 1065 MHz.

6. Reception chain according to one of the preceding claims, in which said sinusoidal signal (107) used by the mixer (106) to mix the signal amplified by the low noise amplifier is a sinusoidal signal whose frequency is substantially equal to 1050 MHz or 1070 MHz.

7. Reception chain according to one of the preceding claims, further comprising one or more bandpass or lowpass filters (108, 123, 133) configured to reject intermodulation lines generated by at least one of the mixer (106), the first frequency transposition device (122) and the second frequency transposition device (132).

8. Reception chain according to one of the preceding claims, further comprising means for oversampling and adjusting the power level (111) of the signals digitized by the analog-digital converter (109).