IFF / ADS-B Reception Channel

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: a dual-band filtering device (103) passing around the frequency bands of the IFF and ADS-B signals while rejecting the intermediate frequency band, a low-noise amplifier (104), a mixer (106) configured to transpose the IFF and ADS-B signals to lower frequencies, 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 processing means (124 / 134) of the signals. Figure for the abbreviation: Fig. 1

Description

Title of the invention: IFF / ADS-B receiving chain technical field

[0001] The invention relates to the field of air traffic control and collision avoidance devices. More specifically, it concerns 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. Prior art

[0002] IFF is an encrypted aircraft identification system that allows civil or military approach radars to recognize cooperating, or "friendly," aircraft and determine their heading and distance. IFF is also used in flight by military aircraft to identify friendly and enemy aircraft. IFF interrogations are conducted 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 Navigation Satellite System (GNSS) and periodically transmits it to ground stations and other aircraft in the vicinity. The 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 TIFF on the 1030 MHz frequency and ADS-B on the 1090 MHz frequency.

[0005] These receiving equipment are subject to stringent performance requirements under the DO-260 B or C (for ADS-B), AIMS 03-1000 (for TIFF), and ED73 E or F (ADS-B) standards. These requirements relate in particular to minimum rejection levels for the receiving radio chains. Specifically, the rejection levels to be achieved are very high (greater than 60 dB) in the 1053 MHz - 1065 MHz band, which lies between the TIFF and ADS-B reception frequencies.

[0006] In order to meet these stringent rejection requirements, state-of-the-art aircraft generally carry separate equipment for TIFF and ADS-B. This equipment has analog input filters designed to achieve the levels of rejection defined by 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 BulkAcoustic Wave, or volume wave filter), etc.).

[0007] Some equipment, such as the Thaies TSC4000, receives IFF interrogations and ADS-B messages in the same device. However, this reception takes place on two separate radio channels.

[0008] Integrating two separate receiving devices or two separate receiving chains in an aircraft to perform IFF and ADS-B receiving functions has obvious consequences in terms of volume and weight, which may not be compatible with small aircraft. Furthermore, the power 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 greater their number, the higher the unit cost.

[0009] An object of the invention is therefore to describe equipment having a single receiving chain allowing continuous reception of 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 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 including the frequencies 1030 MHz and 1090 MHz, - an analog section 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 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 receiving chain according to the invention, the dual-band filtering device is a dual-band filter.

[0013] According to an embodiment of the receiving 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 reject together at least 60dB of signals received outside the frequency bands of reception of IFF and ADS-B signals.

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

[0016] 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.

[0017] According to one embodiment, the receiving 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 device frequency transposition 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-to-digital converter. Brief description of the drawings

[0019] The invention will be better understood and other features, details and advantages will become clearer from the following description, given by way of non-limiting reason, and from the accompanying figures, given by way of example.

[0020] [Fig-1] Fig. 1 represents a functional block diagram of a receiving chain 100 according to one embodiment of the invention.

[0021] [Fig.2] Fig.2 gives an example of a dual-band analog filter template that can be used for the implementation of a receiver according to an embodiment of the invention. Description of the implementation methods

[0022] There are several ways to implement an IFF or ADS-B reception chain. In all cases, the radio signal, whether centered around the frequency of 1030 MHz or 1090 MHz, is filtered and then amplified using a low-noise amplifier, and then filtered again. The filters are necessary to meet the rejection requirements 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.

[0023] The receivers can be heterodyne or homodyne, and the signal digitization is done at a low intermediate frequency, either directly on the radio signal, or on a video signal produced from the radio signal.

[0024] The historical solution consists of performing heterodynic reception of the signal, converting it into a video signal at a low intermediate frequency, and then digitizing the video signal. The conversion of the signal into a video signal involves working solely with the logarithmic envelope of the signal. The advantage of this solution is that it is low cost and requires minimal processing, which is why it is still used, despite its size.

[0025] Another solution involves directly digitizing IFF or ADS-B signals at their carrier frequency using very powerful and high-performance ADCs. However, this solution is expensive to implement, and ADCs are considered critical, complex components that must meet specific aeronautical certification requirements (DO-284 standard), which is why it is not widely used in aeronautical components.

[0026] More recent solutions consist of digitizing the entire received radio signal in the form of I / Q signals. These solutions, whether they originate from a helical reception Therodyne or homodyne reception allows for more powerful digital processing since there is no loss of information related to the conversion of the signal into a video signal.

[0027] Designing a radio chain that allows the simultaneous reception of IFF and ADS-B signals, with stable filtering in the frequency bands of interest and complying with regulatory constraints on signal rejection levels outside these bands, proves to be particularly difficult. Indeed, while it is possible to design analog filters to achieve the desired rejection levels around either the IFF or ADS-S frequency bands, designing analog filters that are simultaneously passable and stable 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 ripple problems in the band, and have significant weight and size.

[0028] The implementation of a high-order digital filter that is passable and stable across both frequency bands of interest and has the desired rejection properties is theoretically possible. However, such a filter would be positioned in the receiving 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 TIFF and ADS-B, particularly those received in the frequency band between the two bands of interest. These unrejected emissions can cause the ADC to operate at saturation. In practice, ADC saturation leads to nonlinear distortion which, at a minimum, creates broadband spectral noise, destroying the receiver's dynamic range, and at worst, will cause damage to the receiver.

[0029] In order to overcome the shortcomings of the prior art, and taking into account the constraints presented above, the invention defines a hybrid analog-digital radio reception chain featuring: - 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 ADC due 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 make it possible to meet the normative requirements.

[0030] Figure 1 represents a functional block diagram of a reception chain 100 according to an embodiment of the invention, allowing the simultaneous reception of signals IFF (1030 MH) and ADS-B (1090 MHz).

[0031] It includes a receiving antenna 101, configured to receive a radio frequency signal in a frequency band including IFF and ADS-B signals, i.e. the frequencies 1030 MHz and 1090 MHz.

[0032] It then includes an analog part 102 configured to provide head processing to the received signals, up to their digitization.

[0033] In this respect, the analog part 102 of the radio chain 100 according to an embodiment of the invention includes a dual-band filtering device 103 configured to filter the radio frequency signal acquired on the receiving antenna 101, passing around the frequency bands of the IFF signals (centered around 1030 MHz) and ADS-B (centered around 1090 MHz) and rejecting the signals outside these bands, in particular those located in the intermediate frequency band.

[0034] According to one embodiment of the invention, the dual-band filtering device 103 may include 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).

[0035] According to another embodiment, the dual-band filtering device 103 can be implemented using a diplexer (a neologism derived from the English word diplexef) that separates 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 QORVO BAW 880367 and 880374 filters. The two channels are then recombined using a combiner. The diplexer and the combiner are designed to ensure proper matching 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 unloaded.

[0036] According to another embodiment of the invention, which is more advantageous because it is more compact and simpler to manufacture, 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; therefore, its dimensions can be more flexible, thus making the manufacture of such an analog filter possible.

[0037] Fig. 2 gives an example of a dual-band analog filter template 103 that can be used for the implementation of a receiver according to an embodiment of the invention.

[0038] This filter is defined as passing between the frequencies fQi = 1005 MHz and fQ2 = 1055 MHz, i.e., in the frequency band associated with the reception of IFF signals. The oscillation of the signals in the sub-band fQOi = 1016 MHz to fQOi = 1044 MHz is limited to 6 dB, so as to minimize distortions of the IFF signal.

[0039] This filter is also defined as passing between the frequencies fAi = 1065 MHz and fA2 = 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 fQOi = 1076 MHz to fQOi = 1104 MHz is limited to 6 dB, so as to minimize distortions of the ADS-B signal.

[0040] Outside these two frequency bands, the rejection level of the filter is greater than 30 dB, in particular in the 1055 MHz - 1063 MHz frequency band, which ensures sufficient rejection to avoid the phenomenon of saturation of the ADC by signals transmitted in this frequency band.

[0041] The analog section 102 of the radio chain 100 according to one embodiment of the invention also includes 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 far from the frequency bands of interest. In the example of [Fig. 1], the bandpass filter 105 is passable over a fairly wide frequency band from 900 MHz to 2 GHz.

[0042] The analog section 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, so as 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 so as to avoid interlacing of the IFF and ADS-B intermodulation lines.

[0043] 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.

[0044] 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.

[0045] 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 CAN compatible.

[0046] According to an advantageous embodiment of a receiving chain 100 according to the invention, the transposition of the signals is followed by a filtering 108 whose purpose 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.

[0047] Finally, the analog section 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 ADC's sampling rate is chosen to be at least twice the frequency of the highest 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.

[0048] The receiving chain 100 also includes a digital part 110 configured to provide the additional filtering necessary to meet regulatory requirements, and to process IFF and ADS-B signals. This digital part can be implemented on computing means 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 means, or any hardware component enabling the processing of the digital part 110 described below.

[0049] According to an advantageous embodiment of the invention, the digital section 110 is configured to implement optional oversampling and power adjustment of the received signals. Oversampling the received signals reduces the sampling rate of the ADC 109, thereby lowering its power consumption. Power adjustment optimizes the dynamic range of the signals to ensure optimal performance of subsequent processing. Alternatively, oversampling can be performed later in the digital section.

[0050] The digital part 110 is further configured to perform a duplication 112 of the signals, and to process them along two separate paths: - a first path 120, where processing is implemented to enable the interpretation of IFF signals, - a second path 130, where processing is implemented to allow the interpretation of ADS-B signals.

[0051] Duplication 112 consists of a copying of the digitized signals (and possibly oversampled and power-adjusted).

[0052] Each of the paths includes a 121 / 131 filtering device and a 122 / 132 frequency transposition device.

[0053] The filtering devices 121 / 131 are configured to filter the signal around the transposed frequency of interest (20 MHz for path 120 associated with the IFF signal and 40 MHz 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 the analog filter 103 and are defined so that together these filters provide the rejection levels defined by the DO-260, AIMS 03-1000, and ED73 standards. They may differ on the IFF path 120 and on the ADS-B path 130 and are adapted to the spectral characteristics of the signals processed on each path. In particular, in addition to the 103 head dual-band filter, they ensure a rejection of more than 60 dB of signals received in the 1053 MHz - 1065 MHz frequency band.

[0054] In the case of a mixture 106 with a sinusoidal signal 107 at a frequency of 1050 MHz, the filter 121 can, for example, be a low-pass filter rejecting signals above 25 MHz by more than 30 dB. Similarly, in the same application, the filter 131 can, for example, be a band-pass filter rejecting signals outside a 50 MHz frequency band centered on 40 MHz by more than 30 dB.

[0055] Frequency transposition devices 122 / 132 are configured to transpose signals to working frequencies, i.e., operating frequencies that allow for subsequent signal analysis processing. For example, in the case of a mix 106 with a sinusoidal signal at a frequency of 1050 MHz, the carrier frequency of the signals for path 120 associated with the IFF signal is 20 MHz and 40 MHz for 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 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 IFF or ADS-B signals. The working frequencies of the IFF and ADS-B signals are not necessarily identical.Advantageously, the frequency transposition devices 122 and 132 can be followed by a low-pass filter 123 / 133 configured to suppress intermodulation lines related to signal transposition.

[0056] On each path, the positions of the filtering device 121 / 131 and the frequency transposition device 122 / 132 can be reversed. In the case of baseband transposition, the filtering devices 121 / 131 can be filters low-pass filter. However, the arrangement shown in [Fig.1] is advantageous since it avoids the appearance of intermodulation lines linked to the presence of the ADS-B signal on the 120 path of the IFF signal and vice versa.

[0057] Finally, each path includes means 124 / 134 for processing the demodulated samples. These processes are not described in detail here because they correspond to known state-of-the-art processes for decoding IFF or ADS-B signals, namely the calculation of cross-correlation products, the conversion of the signals into video signals, and the search for pulses in these signals.

[0058] The receiver chain according to the invention thus makes it possible to receive IFF and ADS-B signals in a combined manner in a compact solution. It comprises an analog section and a digital section, configured to achieve together the rejection performance defined by the DO-260 B and C, AIMS 03-1000, and ED73 E and F standards. It differs from state-of-the-art receiver chains in that rejection is achieved by: - an analog filter located at the head of the processing, designed to protect the ADC from signals that could saturate 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 allow IFF and ADS-B reception.

[0059] It brings: - improved reception management, thanks to the relocation of filtering and demodulation functionalities to the digital part. Indeed, digital processing is more stable, and it is simpler to adjust digital processing than hardware components, and - a minimum reduction by half in the surface area of ​​the 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 helps to reduce costs.

Claims

1. Claims 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 receiving 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 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 (104) configured to amplify the radiofrequency 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 IFF signals transposed 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. A 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 reject together by at least 60dB signals received outside the reception frequency bands of the IFF and ADS-B signals.

5. Reception chain according to one of the preceding claims, wherein 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. A 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).

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