Bistatic radar system based on superheterodyne Rydberg atom receiver

Abstract

The invention provides a bistatic radar system based on a superheterodyne Rydberg atom receiver. The transmitting end and the receiving end of the system are different in position and are synchronized by a timing system device. A system transmitting end transmits a linear frequency modulation signal, and a system receiving end uses a Rydberg atom receiver to receive an echo of a detection signal reflected by a target. The Rydberg atom receiver is of a superheterodyne structure, that is, a receiving end firstly generates a linear frequency modulation signal consistent with a transmitting end based on a timing system device, then inputs the linear frequency modulation signal and a received echo signal into an atom gas chamber together, then measures the spectral change of probe light penetrating through the atom gas chamber, and realizes target detection mainly according to the measured spectral change. And distance measurement and positioning. The system can utilize the advantages of high sensitivity, small size and the like of the Rydberg atom receiver, and overcomes the defect of insufficient instantaneous bandwidth of the atom receiver through special design.

Description

Technical Field

[0001] The present invention relates to the field of radar technology, and in particular to a bistatic radar system based on a superheterodyne Rydberg atomic receiver. Background Art

[0002] Bistatic radar refers to a radar whose receiving end and transmitting end are not in the same location. It has the advantages of low cost, good survivability, and not easy to be interfered with. The transmitting end of the bistatic radar transmits radio waves at an agreed frequency and irradiation direction. The radio waves illuminate the target to produce echoes, and the receiving end completes target detection by detecting the echoes. Due to the different locations, the transmitting end and the receiving end are usually synchronized with a timing device, so that the time from the transmission of the radio wave to the reception of the echo can be measured to calculate the distance, and then the target position can be determined in combination with the azimuth information.

[0003] Bistatic radars based on traditional electronic technology have received a lot of research, but traditional electronic radars, especially the receiving end of the system, have common problems. For example, the radar receiving antenna is often large in size and needs to match the wavelength of the radio wave, making it difficult to work in different frequency bands. At the same time, the development of the RF front end of the electronic system has also faced a bottleneck. At present, quantum sensing technology has made great progress. Related technologies represented by Rydberg atomic receivers have shown the potential to surpass electronic systems, and are expected to break through the noise limitations of electronic systems and realize the miniaturization and full-band reception of radio wave receiving systems.

[0004] The instantaneous bandwidth of a Rydberg atomic receiver is often limited. In particular, a Rydberg atomic receiver based on a superheterodyne structure has good sensitivity but cannot process large-bandwidth wireless signals. If the bandwidth of the signal transmitted by the radar is too small, it will not only affect the target echo intensity, but also deteriorate the resolution and accuracy of the target distance measurement. At the same time, traditional Rydberg receivers often require laser frequency scanning and then measure the degree of splitting or offset of the laser spectrum to achieve radio signal reception, so laser frequency conversion needs to be set, resulting in a more complex system.

[0005] In summary, how to design a radar system that can process large-bandwidth wireless signals based on the characteristics of the Rydberg atom receiver and provide an effective target detection and positioning solution is an urgent problem to be solved. Summary of the invention

[0006] The present invention provides a bistatic radar system based on a superheterodyne Rydberg atomic receiver, aiming to design a radar system capable of processing large-bandwidth wireless signals based on the characteristics of the Rydberg atomic receiver, and provide an effective target detection and positioning solution to optimize the bistatic radar design and improve system performance.

[0007] The present invention provides a bistatic radar system based on a superheterodyne Rydberg atomic receiver, comprising a transmitting end, a receiving end and a time synchronization device, wherein the transmitting end comprises a first information source and a directional antenna; the receiving end comprises a Rydberg atomic receiver, a second information source and a signal processing module;

[0008] The first information source generates a linear frequency modulation signal A and transmits it through the directional antenna; the second information source generates a linear frequency modulation signal B; the first information source and the second information source are synchronized by using the timing device so that the parameters of the linear frequency modulation signal A and the linear frequency modulation signal B are consistent; the Rydberg atomic receiver receives an external signal, and inputs the external signal and the linear frequency modulation signal B into the atomic gas chamber to detect the EIT transmission peak intensity to obtain an output signal; the signal processing module locates the detection target according to the output signal and the transmission direction of the directional antenna; wherein the external signal includes an echo signal generated after the linear frequency modulation signal A is irradiated onto the detection target.

[0009] Further, the signal processing module includes a filtering unit, an A / D unit, a spectrum analysis unit and a target positioning unit;

[0010] The filtering unit filters the output signal to eliminate high-frequency components in the output signal to obtain a filtered signal; the A / D unit samples the filtered signal to obtain a sampled signal; the spectrum analysis unit performs spectrum calculation on the sampled signal and compares each spectrum peak with a set threshold; the target positioning unit positions the detection target corresponding to the spectrum peak greater than the set threshold according to the transmission direction of the directional antenna.

[0011] Furthermore, the target positioning unit positions the detection target corresponding to the spectrum peak greater than the set threshold according to the transmission direction of the directional antenna, specifically including:

[0012] The frequency of the spectrum peak greater than the set threshold is determined, the delay of the echo signal is calculated according to the frequency, and the distance between the detection target and the transmitting end along the transmission direction of the directional antenna is calculated according to the delay and the pre-agreed distance between the transmitting end and the receiving end.

[0013] Furthermore, the parameters of the linear frequency modulation signal A or the linear frequency modulation signal B include a starting frequency, a tuning frequency, a starting time and a period.

[0014] Beneficial effects of the present invention:

[0015] (1) The bistatic radar system provided by the present invention is based on the design of superheterodyne Rydberg atomic receiver. Compared with the traditional bistatic radar, the present invention can effectively utilize the advantages of Rydberg atomic receiver such as small size and wide operating frequency band, making the system more portable and universal. Since the sensitivity of the atomic receiver can approach the standard quantum limit, the system of the present invention also has high detection performance.

[0016] (2) The present invention takes full account of the structure and performance characteristics of the Rydberg atomic receiver. Compared with other existing detection systems based on this type of receiver, the advantages are mainly reflected in two points. First, the present invention creatively changes the design of the superheterodyne part of the Rydberg atomic receiver, synchronously accesses the linear frequency modulation signal, and extracts the echo delay information through spectrum peak detection and frequency estimation, thereby overcoming the problem of limited instantaneous receiving bandwidth of the Rydberg atomic receiver. Therefore, the radar system of the present invention can achieve better target detection and positioning accuracy; second, the present invention mainly completes detection based on the influence of radio waves on spectral intensity in the EIT effect, and does not need to let the coupled light sweep the frequency like other Rydberg atomic receivers, and then measure the degree of spectrum splitting or deviation, which simplifies the system complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a working scenario of a bistatic radar system based on a superheterodyne Rydberg atomic receiver provided in an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of the structure of a superheterodyne Rydberg atomic receiver provided by an embodiment of the present invention;

[0019] Figure 3 A graph of a transmission signal and an echo signal provided by an embodiment of the present invention;

[0020] Figure 4 A signal graph after filtering the output signal of the atomic receiver provided in an embodiment of the present invention;

[0021] Figure 5 A processing flow chart of a signal processing module provided by an embodiment of the present invention;

[0022] Figure 6 A schematic diagram of a positioning scenario provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The terms "first", "second", "A", "B", etc. in the present invention are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more.

[0025] like Figure 1 As shown, an embodiment of the present invention provides a dual-base radar system based on a superheterodyne Rydberg atomic receiver, including a transmitting end, a receiving end and a timing device, wherein the transmitting end includes a first information source and a directional antenna; the receiving end includes a Rydberg atomic receiver, a second information source and a signal processing module.

[0026] Specifically, when the radar system is working, the first information source generates a linear frequency modulation signal A and transmits it through the directional antenna; the second information source generates a linear frequency modulation signal B; the first information source and the second information source are synchronized by the timing device so that the parameters of the linear frequency modulation signal A and the linear frequency modulation signal B are consistent; the Rydberg atomic receiver receives an external signal, and inputs the external signal and the linear frequency modulation signal B into the atomic gas chamber to detect the EIT transmission peak intensity to obtain an output signal; the signal processing module locates the detection target according to the output signal and the transmission direction of the directional antenna; wherein the external signal includes an echo signal (also called a target echo) generated after the linear frequency modulation signal A is irradiated onto the detection target.

[0027] In this embodiment, the first information source and the second information source are both wireless information sources. Since the transmitting end and the receiving end are far apart, the timing equipment is placed at the transmitting end and the receiving end to synchronize the wireless information sources of the transmitting end and the receiving end. At the transmitting end, the wireless information source continuously transmits a linear frequency modulation signal to illuminate a certain direction, and the parameters of the linear frequency modulation signal specifically include the starting frequency, tuning frequency, starting time and period. That is, it should be ensured that the wireless information source signal at the receiving end is the same as the linear frequency modulation signal at the transmitting end in terms of parameters such as starting frequency, frequency modulation slope, starting time and period. The strength of the wireless information source signal at the receiving end should be as strong as possible while ensuring that there is no overflow in the Rydberg atomic receiver.

[0028] It should be noted that the parameters of the linear frequency modulation signal can be adjusted, but in a detection process, once the parameters of the linear frequency modulation signal are specified, they are fixed. At the same time, the location of the transmitter, the parameters of the transmitted linear frequency modulation signal, the transmission direction of the directional antenna, and the location of the receiver are pre-specified by the system, and the receiver knows the above information.

[0029] like Figure 2 As shown, in this embodiment, the Rydberg atomic receiver is a superheterodyne structure, mainly including a detection light laser, a coupling light laser, an atomic gas chamber and a photodetector. The relevant devices are configured according to the standard structure of the Rydberg receiver to ensure that the detection light laser and the coupling light laser each emit lasers to pass through the atomic gas chamber in opposite directions. It can be understood that the working principle of the Rydberg atomic receiver is as follows: the detection light emitted by the detection light laser and the coupling light emitted by the coupling light laser excite the atoms in the atomic gas chamber to the Rydberg state, and induce the electromagnetically induced transparency (EIT) effect. The photodetector can record the spectral peak intensity of the detection light penetrating the atomic gas chamber, and convert it into an electrical signal (i.e., the output signal of the Rydberg atomic receiver) for subsequent signal processing module analysis.

[0030] At the receiving end, the received external wireless signal (including the target echo) and the linear frequency modulation signal generated by the wireless source are input into the atomic gas chamber together and interact with the atoms, which will cause the intensity of the spectral peak (i.e., the EIT transmission peak) of the detection light transmitted through the atomic gas chamber to change with the size of the external wireless signal. The photodetector can record the EIT transmission peak intensity and convert it into an electrical signal. Therefore, the output signal of the photodetector (i.e., the electrical signal converted from the EIT transmission peak intensity) can reflect the information carried in the external wireless signal, especially the target echo information. Therefore, the signal processing module can complete target detection, distance measurement and positioning by analyzing the electrical signal converted from the EIT transmission peak intensity.

[0031] It should be noted that Figure 2 The figure shows that both the external wireless signal and the linear frequency modulation signal B generated by the second signal source are input into the atomic gas chamber through their respective antennas. In practical applications, it can also be implemented in other ways, such as converting the external wireless signal into current through the antenna, combining it with the linear frequency modulation signal generated by the wireless signal source in the combiner, and then converting it into electromagnetic wave input through the antenna.

[0032] In conjunction with the diagram, the following quantitatively analyzes the changes in the input and output signals of the Rydberg atomic receiver at the receiving end of the present invention by taking single target detection as an example.

[0033] Figure 3 It is a schematic diagram of a single cycle speech diagram of the transmitted signal and the echo signal. Figure 3 The red line in the middle represents the transmitted signal, and the signal amplitude is assumed to be A1. The starting frequency is f0, and the mathematical expression of the single-cycle transmitted signal is

[0034] s(t)=A1cos(2πf0t+πut 2 )

[0035] Where u represents the frequency modulation slope of the linear frequency modulation signal.

[0036] Figure 3 The blue dotted line in the middle represents the echo signal. Assuming that a single target exists and its echo signal delay is τ (τ is less than the linear frequency modulation signal period T), the external wireless signal at the receiving end can be expressed as

[0037] s(t)=A2 cos(2πf0(t-τ)+πu(t-τ) 2 )+ω(t)

[0038] Where A2 represents the echo intensity and ω(t) represents the noise.

[0039] like Figure 3 As shown in the figure, due to the particularity of the linear frequency modulation signal, the delay of the echo and the transmission signal is also reflected in the frequency difference △f between the two at the same time, that is, △f = uτ. After the above two signals are input into the atomic gas chamber, due to the EIT effect, the intensity of the light transmitted by the atomic gas chamber changes with the change of the external wireless signal. Figure 2 The signal after photoelectric conversion can be expressed as

[0040]

[0041] Where ω′(t) represents the noise term. The first term in the above formula represents the difference frequency component between the external wireless signal and the wireless source signal at the receiving end, and the second term represents the high-order harmonic interference. n represents the amplitude of the nth-order harmonic, φ n (t) represents its phase.

[0042] It can be understood that since the harmonic frequency is higher, the harmonic can be suppressed by filtering, so that only the first term of the above formula is retained. Figure 4 is the signal graph after filtering. After filtering, the signal is in the form of a cosine wave with a frequency of △f = uτ, so by measuring the size of this frequency component, the echo delay τ can be estimated.

[0043] contrast Figure 3 and Figure 4It can be found that the bandwidth of the original linear frequency modulation signal is B = uT, while the bandwidth of the receiver output signal is △f = uτ. Usually the echo delay τ<<T, so the bandwidth is significantly reduced. The reason for the above changes is that the atomic gas chamber can respond to the difference frequency component of the external wireless signal and the wireless source signal at the receiving end, and the bandwidth of the difference frequency component is △f = uτ. Therefore, in practical applications, the present invention can use a linear frequency modulation signal with a larger bandwidth for detection to improve the detection effect and distance measurement accuracy; at the same time, it overcomes the problem of insufficient instantaneous receiving bandwidth of the atomic receiver.

[0044] In one embodiment, Figure 5 As shown, the signal processing module includes a filtering unit, an A / D unit, a spectrum analysis unit and a target positioning unit. Correspondingly, the processing flow of the signal processing module specifically includes: the filtering unit filters the output signal to eliminate the high-frequency components in the output signal to obtain a filtered signal; the A / D unit samples the filtered signal to obtain a sampled signal; the spectrum analysis unit performs spectrum calculation on the sampled signal and compares each spectrum peak with a set threshold; the target positioning unit locates the detection target corresponding to the spectrum peak greater than the set threshold according to the transmission direction of the directional antenna.

[0045] Specifically, the filter unit first needs to perform low-pass filtering on the output signal of the atomic receiver, that is, let the signal pass through a low-pass filter. This is to filter out the high-frequency harmonic interference discussed above. The cutoff frequency of the low-pass filter is set to uτ max , where τ max Represents the maximum possible delay of the target echo. The filtered signal is then sampled using the A / D unit, with an A / D sampling rate of f s ≥2uτ max Then the spectrum of the sampled signal is calculated, and the spectrum peaks are compared one by one to see if they are greater than the set threshold: if they are greater than the threshold, the target is considered to be detected and positioned, and the target position parameters are output after positioning, and then other spectrum peaks are processed; otherwise, the spectrum peak is not considered to correspond to the target, and other spectrum peaks are directly processed until all spectrum peaks are processed. The actual threshold setting can refer to the classic spectrum detection method, and the threshold is determined by the current background noise level.

[0046] In one embodiment, Figure 6 As shown, in the positioning scenario of the present invention, the system transmitter transmits a linear frequency modulation signal in the direction of the azimuth angle θ by a directional antenna. Assume that the distance R i There is a target at the location (denoted as target i), and the signal generates an echo after it hits the target. The echo propagation distance is D i Then it is received by the receiving end. The straight-line distance between the transmitting end and the receiving end is d(R i ,D i ,d form a triangle).

[0047] Therefore, the target positioning unit locates the detection target corresponding to the spectrum peak greater than the set threshold according to the transmission direction of the directional antenna, specifically including: if it is determined that the i-th spectrum peak is greater than the threshold, the target corresponding to the i-th spectrum peak (target i) will be located. i Reverse target echo delay τ i =f i / u. but Figure 6 The distance L traveled by the echo signal i =R i +D i =τ i c, where c represents the speed of light. The receiving end also knows the azimuth angle θ of the linear frequency modulation signal transmitted by the directional antenna. Then Figure 6 , which can be calculated based on the relationship between the sides and angles of trigonometric functions Finally, it is determined that the target is located at the transmitting end position θ, and the distance R i The output target parameter of the signal processing module is θ,R i .

[0048] It can be understood that the system of the present invention can detect targets in the transmission direction of the current directional antenna of the transmitter at a time. When detecting a certain area, the transmitter adjusts the transmission direction of the directional antenna in sequence to complete the detection of all targets in the area.

[0049] The present invention is applicable to ultrashort wave to microwave frequency band signals (mainly in the frequency range of 30MHz to 10GHz), and the signal propagates in a straight line from the transmitting end to the target, and the echo signal propagates from the target to the receiving end. The specifications of the synchronization equipment in the system described in the present invention are not limited, but the time reference accuracy provided by the synchronization equipment is required to be better than 10ns, and the frequency reference accuracy is better than 10 -9 Hz. It is assumed that during a detection, the target has no obvious distance movement and there is no strong interference of the same frequency in the environment.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bistatic radar system based on a superheterodyne Rydberg atomic receiver, comprising a transmitting end, a receiving end and a time synchronization device, characterized in that: The transmitting end includes a first information source and a directional antenna; the receiving end includes a Rydberg atom receiver, a second information source and a signal processing module; The first information source generates a linear frequency modulation signal A and transmits it through the directional antenna; the second information source generates a linear frequency modulation signal B; the first information source and the second information source are synchronized by using the timing device so that the parameters of the linear frequency modulation signal A and the linear frequency modulation signal B are consistent; the Rydberg atomic receiver receives an external signal, and inputs the external signal and the linear frequency modulation signal B into the atomic gas chamber to detect the EIT transmission peak intensity to obtain an output signal; the signal processing module locates the detection target according to the output signal and the transmission direction of the directional antenna; wherein the external signal includes an echo signal generated after the linear frequency modulation signal A is irradiated onto the detection target.

2. A bistatic radar system based on a superheterodyne Rydberg atomic receiver according to claim 1, characterized in that: The signal processing module includes a filtering unit, an A / D unit, a spectrum analysis unit and a target positioning unit; The filtering unit filters the output signal to eliminate high-frequency components in the output signal to obtain a filtered signal; the A / D unit samples the filtered signal to obtain a sampled signal; the spectrum analysis unit calculates the spectrum of the sampled signal and compares each spectrum peak with a set threshold; The target positioning unit positions the detection target corresponding to the spectrum peak greater than a set threshold according to the transmission direction of the directional antenna.

3. A bistatic radar system based on a superheterodyne Rydberg atomic receiver according to claim 2, characterized in that: The target positioning unit locates the detection target corresponding to the spectrum peak greater than the set threshold according to the transmission direction of the directional antenna, specifically including: The frequency of the spectrum peak greater than the set threshold is determined, the delay of the echo signal is calculated according to the frequency, and the distance between the detection target and the transmitting end along the transmission direction of the directional antenna is calculated according to the delay and the pre-agreed distance between the transmitting end and the receiving end.

4. A bistatic radar system based on a superheterodyne Rydberg atomic receiver according to any one of claims 1 to 3, characterized in that: The parameters of the linear frequency modulation signal A or the linear frequency modulation signal B include a starting frequency, a tuning frequency, a starting time and a period.

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