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 portion (102) with: either a dual-band filtering device (103) that passes the frequency bands of the IFF and ADS-B signals while rejecting the intermediate frequency band, or a low-noise amplifier (104), or a mixer (106) configured to transpose the IFF and ADS-B signals to lower frequencies, or an analog-to-digital converter (109), - a digital portion (110) configured to duplicate the digitized signal (112), and to process the duplicated signals respectively into a first IFF path (120) and a second ADS-B path (130), each of which comprises a filtering device (121 / 131), a frequency transposition device (122 / 132), and processing means (124 / 134) of the signals.

Description

IFF / ADS-B receiving chain Technical field The invention falls within the field of air traffic control and anti-collision devices. More specifically, it relates to a receiving chain configured to allow the simultaneous reception of IFF (Identification Friend or Foe) and ADS-B (Automatic Dependent Surveillance-Broadcast) interrogations, while ensuring strong third-party signal rejection. Previous technique IFF is an encrypted aircraft identification system that allows civilian and military approach radars to recognize cooperating aircraft, referred to as "friends," and determine their heading and distance. IFF is also used in flight by military aircraft to identify friendly and enemy aircraft. IFF interrogations are performed by ground stations or aircraft in a frequency band centered around 1030 MHz, typically 14 MHz. ADS-B is a cooperative surveillance system for air traffic control. An aircraft equipped with ADS-B determines its position using a Global Navigation Satellite System (GNSS) and periodically transmits it to ground stations and other aircraft in the vicinity. The frequency of position transmission depends on the phase of flight. ADS-B transmissions are made in a frequency band centered around 1090 MHz, typically 16 MHz. Most aircraft, particularly airplanes, carry on board the equipment necessary to implement these two standards, in particular, the equipment needed to listen to IFF on the 1030 MHz frequency and ADS-B on the 1090 MHz frequency. These receiving equipment are subject to strict performance restrictions by standards DO-260 B or C (for ADS-B), AIMS 03-1000 (for IFF), and ED73 E or F (ADS-B). These restrictions pertain, in particular, to minimum rejection levels for receiving radio chains. Specifically, the rejection levels that must be achieved are very high (greater than 60 dB) in the 1053 MHz–1065 MHz band, which lies between the IFF and ADS-B receiving frequencies. In order to meet these stringent rejection restrictions, state-of-the-art aircraft typically carry separate equipment for IFF and ADS-B. This equipment includes analog headend filters designed to achieve the rejection levels defined by the standards, cascading a significant number of bandpass filters of various technologies (ceramic cavities, SAW filters (Surface Acoustic Waves), BAW filters (Bulk Acoustic Waves), etc.). Certain receivers, such as the Thales TSC4000, can receive both IFF interrogations and ADS-B messages on the same unit. However, these receptions are performed on two separate radio chains. Carrying two different receivers or two separate receiver chains on board an aircraft to perform IFF and ADS-B reception functions has obvious consequences in terms of size and weight, which may not be suitable for small aircraft. Furthermore, the equipment's power consumption is not optimal, which is a major drawback for drone applications. Finally, the components for each receiver chain are relatively expensive, and the more components there are, the higher the overall production cost. Document CN 109.379.102 A: "Multichannel frequency agility RT unit" describes a multi-function aerospace radio, which aims to reuse the RF chain for receiving signals implemented according to different communication standards (ATC, JIDS, IFF, ADS-B). The document Mansour et al.: "Multiband superconducting filters" deals with the realization of an analog triband filter for IFF transponder, which passes around 1030 MHz and 1090 MHz. Document FR 3.109.451 A1 describes a ground radar that ensures simultaneous IFF interrogations and the reception of ADS-B "squitters" (spontaneous signals). US 2003 / 233192 A1: "Integrated airbone transponder and collision avoidance system" presents a radio post configured to receive IFF and ADS-B signals at 1030 MHz and 1090 MHz. Helfrick: "A surveillance receiver for evaluating mode A / C / S activity". This article describes equipment configured to monitor IFF activity in the 1030 MHz and 1090 MHz frequency bands. Therefore, one purpose of the invention is to describe equipment having a single receiving chain that allows continuous reception of IFF interrogations around the frequency of 1030 MHz and ADS-B emissions around the frequency of 1090 MHz, while respecting the regulatory restrictions associated with these receptions. Summary of the invention To this end, the present invention describes a receiving chain configured to allow the reception of IFF signals received in a frequency band centered on 1030 MHz and ADS-B signals received in a frequency band centered on 1090 MHz, and to reject at least one frequency band between 1030 MHz and 1090 MHz. The receiving chain according to the invention comprises: - a receiving antenna configured to receive a radio frequency signal in a frequency band comprising the frequencies of 1030 MHz and 1090 MHz, - an analog part with: a dual-band filtering device configured to filter the radio frequency signal acquired at the receiving antenna, passing around the frequency bands of the IFF and ADS-B signals, while rejecting said frequency band between the frequency of 1030 MHz and the frequency of 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 to transpose the signals received in 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 in these lower frequency bands. It also includes a digital part configured to duplicate the digitized signal and to process the duplicated signals respectively in: - a first path comprising a first filtering device and a first frequency transposing 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 route comprising a second filtering device and a second frequency transposing 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. According to one embodiment of the receiving chain according to the invention, the dual-band filtering device is a dual-band filter. According to one embodiment of the receiving chain according to the invention, the dual-band filtering device is configured to reject by at least 30 dB the signals received in said frequency band between the frequency of 1030 MHz and the frequency of 1090 MHz. Advantageously, the dual-band filtering device, the first filtering device and the second filtering device are configured to reject together by at least 60 dB signals received outside the reception frequency bands of the IFF and ADS-B signals. According to one embodiment of the receiving chain according to the invention, the frequency band between the frequency of 1030 MHz and the frequency of 1090 MHz comprises the frequency band of 1053 MHz - 1065 MHz. According to one embodiment of the receiving 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. According to one embodiment, the receiver chain according to the invention further comprises one or more bandpass or lowpass filters configured to reject intermodulation lines generated by at least not from among the mixer, the first frequency transposition device and the second frequency transposition device. According to one embodiment, the receiving chain according to the invention further comprises means for oversampling and adjusting the power level of the signals digitized by the analog-to-digital converter. Brief description of the figures The invention will be better understood and other features, details and advantages will be more clearly revealed by reading the following description, which is given by way of non-limitation, and by referring to the accompanying figures, which are given by way of example, among which: - Figure 1 represents a functional synopsis of a receiving chain 100, according to one embodiment of the invention. - Figure 2 gives an example of a dual-band analog filter template that can be used for the implementation of a receiver, according to one embodiment of the invention. Detailed description There are several ways to implement an IFF or ADS-B receiving chain. In all cases, the radio signal, whether centered around 1030 MHz or 1090 MHz, is filtered, then amplified using a low-noise amplifier, and then filtered again. The filters are necessary to meet the rejection restrictions of the DO-260, AIMS 03-1000, and ED73 standards. The signal is then either directly digitized or converted to a video signal and subsequently digitized. Receivers can be heterodyne or homodyne, and the digitization of the signal is done at low intermediate frequency, either directly on the radio signal or on a video signal produced from the radio signal. The traditional solution involves heterodyning the signal, converting it into a video signal at a low intermediate frequency, and then digitizing the video signal. The video conversion process involves working solely with the logarithmic envelope of the signal. The advantage of this solution is its low cost and minimal processing requirements, which explains its continued use despite its complexity. Another solution involves directly digitizing IFF or ADS-B signals at their carrier frequency, using powerful, high-performance CAN buses. However, this solution is expensive to implement and makes CAN buses critical complex components that must comply with specific aeronautical certification restrictions (DO-284 standard), which is why they are rarely used in aerospace applications. More recent solutions involve digitizing the entire received radio signal as I / Q signals. These solutions, whether from heterodyne or homodyne reception, allow for more powerful digital processing, as there is no loss of information associated with converting the signal into a video signal. Designing a radio chain that allows simultaneous reception of IFF and ADS-B signals, with stable filtering in the frequency bands of interest and respecting regulatory restrictions on signal rejection levels outside these bands, proves to be particularly difficult. Indeed, while it is possible to design analog filters that achieve the desired rejection levels around one or the other of the IFF or ADS-B frequency bands, designing stable, pass-through analog filters simultaneously around both frequencies of interest, while guaranteeing the required rejection levels (greater than 60 dB) outside these bands, and particularly in the intermediate frequency band, requires the use of particularly high-order filters. Such filters are particularly complex and expensive to produce, exhibit band ripple problems, and are quite heavy and bulky. Implementing a high-order digital filter that is stable and passes through both frequency bands of interest and possesses the desired rejection properties is theoretically possible. However, such a filter would be positioned in the receiving chain after the CAN (analog-to-digital converter), which would therefore not be protected against high-level emissions occurring in frequency bands close to those of the IFF and ADS-B, particularly those received in the frequency band between the two bands of interest. These unrejected emissions can cause the CAN to saturate. In practice, CAN saturation leads to nonlinear distortion, which at the very least creates broadband spectral noise, disrupting the receiver's dynamics and, in the worst case, causing receiver degradation. In order to mitigate the shortcomings of the prior art, and taking into account the restrictions presented above, the invention defines a hybrid analog-digital radio receiving chain that features: - a first level of dual-band analog filtering, intended to provide some 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 CAN saturation related to non-essential radiation, then - a second level of digital filtering, adapted to one or the other of the signals of interest, configured so that the two levels of filtering together allow the regulatory requirements to be met. Figure 1 represents a functional synopsis of a 100 receiving chain, according to one embodiment of the invention, which allows simultaneous reception of IFF (1030 MHz) and ADS-B (1090 MHz) signals. 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 of 1030 MHz and 1090 MHz. It then comprises an analog section 102 configured to provide headend processing to the received signals, up to their digitization. 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 radio frequency signal acquired at 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. According to one embodiment of the invention, the dual-band filtering device 103 may comprise one or more cascaded analog bandpass filters, intended to filter the signal around the IFF frequency band (1030 MHz) and around the ADS-B frequency band (1090 MHz). According to another embodiment, the dual-band filtering device 103 can be implemented using a diplexer that separates the signal into two paths. Each path is then filtered by a bandpass filter designed to filter signals around the IFF (1030 MHz) and ADS-B (1090 MHz) frequency bands, for example, the QORVO BAW 880367 and 880374 filters. The two paths are then recombined using a combiner. The diplexer and combiner are designed to ensure good matching of each path to the two frequencies of interest, IFF (1030 MHz) and ADS-B (1090 MHz), for example, using quarter-wave lines, loaded or unloaded. According to another, more advantageous embodiment of the invention, which is more compact and simpler to implement, 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 it does not comply with the restrictions defined by the standards. Therefore, its design can be more flexible, thus making the implementation of such an analog filter possible. Figure 2 gives an example of a dual-band analog filter template 103 that can be used for the implementation of a receiver, according to one embodiment of the invention. This filter is defined as pass-through between the frequencies fQ1 = 1005 MHz and fQ2 = 1055 MHz, that is, in the frequency band associated with the reception of IFF signals. The oscillation of the signals in the sub-band fQ01 = 1016 MHz to fQ01 = 1044 MHz is limited to 6 dB, to minimize distortions of the IFF signal. This filter is also defined as passing between the frequencies fA1 = 1065 MHz and fA2 = 1115 MHz, that is, in the frequency band associated with the reception of ADS-B signals. The oscillation of the signals in the sub-band fQ01 = 1076 MHz to fQ01 = 1104 MHz is limited to 6 dB to minimize distortion of the ADS-B signal. Outside these two frequency bands, the filter's rejection level is greater than 30 dB, particularly in the 1055 MHz - 1063 MHz frequency band, ensuring sufficient rejection to prevent CAN saturation by signals transmitted in this frequency band. The analog portion 102 of the radio chain 100, according to one embodiment of the invention, also comprises a low-noise amplifier 104 configured to amplify the radio frequency signal filtered by the dual-band filtering device 103. Advantageously, the amplifier can be followed by a bandpass filter 105 configured to reject signals outside the frequency bands of interest. In the example shown in Figure 1, the bandpass filter 105 is pass-through over a fairly wide frequency band ranging from 900 MHz to 2 GHz. The analog portion 102 of the radio chain 100, according to one embodiment of the invention, further comprises a mixer 106 configured to mix the signal amplified by the low-noise amplifier (and optionally filtered by the filter 105) with a sinusoidal signal 107, in order to transpose the signals received in the frequency bands of the IFF and ADS-B signals to lower frequency bands that can be digitized by the analog-to-digital converter. Such a mixer is characteristic of a heterodyne receiver. The frequency of the sinusoidal signal 107 is chosen to avoid interlacing phenomena of the IFF and ADS-B intermodulation lines. An advantageous frequency for the sinusoidal signal is a frequency close to 1050 MHz, which allows the IFF signal to be transposed to the frequency of 20 MHz and the ADS-B signal to the frequency of 40 MHz, while preventing intermodulation lines from appearing in the bands of the frequencies of interest. Another advantageous frequency for the sinusoidal signal is a frequency close to 1070 MHz, which allows the IFF signal to be transposed to the frequency of 40 MHz and the ADS-B signal to the frequency of 20 MHz, while preventing intermodulation lines from appearing in the bands of the frequencies of interest. Other frequencies are possible, with the exception of those near 1060 MHz, which would cause IFF intermodulation lines to appear in the ADS-B frequency band and vice versa. Specifically, the frequency can be lower than 1030 MHz or higher than 1090 MHz, provided that the transposed frequencies of the signals of interest are compatible with CAN. According to an advantageous embodiment of a receiver chain 100 according to the invention, the transposition of the signals is followed by a filtering 108, the purpose of which is to suppress 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 cutoff frequency of 70 MHz. Finally, the analog portion 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 frequency of the highest transposed signal, in order to comply with Shannon's theorem. The ADC is selected so that its noise figure is compatible with the expected reception performance. The receiving chain 100 also comprises a digital part 110 configured to provide the necessary filtering to comply with regulatory restrictions and to process the IFF and ADS-B signals. This digital part can be implemented in computing devices such as, for example, a microprocessor, a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), an ASIC (Application-Specific Integrated Circuit), any combination of these devices, or any physical component that allows the processing of the digital part 110 described below. According to an advantageous embodiment of the invention, the digital part 110 is configured to implement optional processing operations 111 for oversampling and power adjustment of the received signals. Oversampling the received signals allows the sampling rate of the CAN 109 to be reduced, thereby lowering its power consumption. Power adjustment of the signals allows their dynamics to be positioned in the best possible way, in order to operate subsequent processing in optimal conditions. Alternatively, oversampling can be performed later in the digital part. The digital section 110 is also configured to perform a duplication 112 of the signals and to process them according to two separate paths: - a first route 120, where processing is implemented that allows the interpretation of IFF signals, - a second route 130, where processing is implemented that allows the interpretation of ADS-B signals. Duplication 112 consists of a copy of the digitized signals (and, eventually, oversampled and adjusted in power). Each of the routes comprises a filtering device 121 / 131 and a frequency transposition device 122 / 132. Filtering devices 121 / 131 are configured to filter the signal around the transposed frequency of interest (the 20 MHz frequency for path 120 associated with the IFF signal and the 40 MHz frequency for path 130 associated with the ADS-B signal, in the case of a mix 106 with a sinusoidal signal 107 at a frequency of 1050 MHz). These filters are complementary to those performed by analog filter 103 and are defined so that together they provide the rejection levels defined by standards DO-260, AIMS 03-1000, and ED73. They may differ for IFF path 120 and ADS-B path 130 and are adapted to the spectral pattern of the signals processed in each path. In particular, they ensure, as a complement to the Abecer 103 dual-band filter, a rejection of over 60 dB of the signals received in the 1053 MHz - 1065 MHz frequency band. In the case of a mix 106 with a sinusoidal signal 107 at a frequency of 1050 MHz, filter 121 could be, for example, a low-pass filter that rejects signals above 25 MHz by more than 30 dB. Similarly, in the same application, filter 131 could be, for example, a band-pass filter that rejects signals outside a 50 MHz frequency band centered at 40 MHz by more than 30 dB. Frequency transposing devices 122 / 132 are configured to transpose signals to operating frequencies, that is, frequencies that enable further signal analysis and processing. For example, in the case of a 106 mix with a sinusoidal signal at a frequency of 1050 MHz, the carrier frequency for the signals on path 120 associated with the IFF signal is 20 MHz, and 40 MHz for path 130 associated with the ADS-B signal. The frequency transposing 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 transposing device can be a mixer configured to transpose the signals to a carrier frequency suitable for processing the IFF or ADS-B signals.The operating frequencies of the IFF and ADS-B signals are not necessarily identical. Advantageously, frequency transposing devices 122 and 132 can be followed by a low-pass filter 123 / 133 configured to suppress intermodulation lines related to signal transposition. In each path, the positions of filter device 121 / 131 and frequency transposition device 122 / 132 can be reversed. In the case of a baseband transposition, filter devices 121 / 131 can be low-pass filters. However, the arrangement shown in Figure 1 is advantageous because it avoids the occurrence of intermodulation lines related to the presence of the ADS-B signal in path 120 of the IFF signal, and vice versa. Finally, each route comprises 124 / 134 processing steps for the demodulated samples. These processing steps are not described in detail herein, as they correspond to known prior art processing steps that enable 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. Therefore, the receiver chain according to the invention allows the combined reception of IFF and ADS-B signals in a compact solution. It comprises an analog and a digital section, configured to achieve together the rejection performance defined by standards DO-260 B and C, AIMS 03-1000, and ED73 E and F. It differs from prior art receiver chains in that rejection is provided simultaneously by: - an analog filter located at the processing head, intended to protect the CAN bus from signals that could saturate it, in particular, from signals transmitted in the frequency band between the IFF signal frequency band and the ADS-B signal frequency band, - Digital filters located after the CAN, intended to provide the additional filtering required to enable IFF and ADS-B receptions. It contributes: - improved reception management, thanks to the shift of filtering and demodulation functions to the digital component. Indeed, digital processing is more stable and it is easier to adjust digital processing than hardware components, and - a reduction, at least by half, of the surface area of ​​the IFF and ADS-B receiving 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. A receiving chain (100) configured to allow the reception of IFF signals received in a frequency band centered on 1030 MHz and ADS-B signals received in a frequency band centered on 1090 MHz, and to reject at least one frequency band between 1030 MHz and 1090 MHz, characterized in that it comprises: - a receiving antenna (101) configured to receive a radio frequency signal in a frequency band comprising 1030 MHz and 1090 MHz, - an analog part (102) with: a dual-band filtering device (103) configured to filter the radio frequency signal acquired at the receiving antenna, passing around the frequency bands of the IFF and ADS-B signals, while simultaneously rejecting said frequency band between 1030 MHz and 1090 MHz. 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) to transpose the received signals in the frequency bands of the IFF and ADS-B signals to lower frequency bands, an analog-to-digital converter (109) configured to digitize the received signals in said lower frequency bands, - a digital part (110) configured to duplicate the digitized signal (112) and to process the duplicated signals respectively in: a first path (120) comprising a first filtering device (121) and a first frequency transposing device (122),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 IFF signal processing means (124), 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 ADS-B signal processing means (134).

2. Receiving chain according to claim 1, wherein said dual-band filtering device (103) is a dual-band filter.

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

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

5. Receiving chain according to any of the preceding claims, wherein said frequency band between 1030 MHz and 1090 MHz comprises the frequency band from 1053 MHz to 1065 MHz.

6. Receiving chain according to any of the preceding claims,wherein the 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. A receiving chain according to any 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 transposing device (122), and the second frequency transposing device (132).

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

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