Secondary radar quantum inquiry receiver

Abstract

The invention relates to the technical field of microwave lasing, and discloses a secondary radar quantum inquiry receiver which comprises a resonant cavity, a gain medium arranged in the resonant cavity and a stimulated radiation source arranged in the resonant cavity. The problems of low sensitivity and the like in the prior art are solved.

Description

Technical Field

[0001] The invention relates to the field of microwave maser technology, in particular to a secondary radar quantum interrogation receiver. Background Art

[0002] Microwave maser technology uses stimulated radiation between electron or atomic nucleus energy levels to amplify electromagnetic waves. Due to its high gain and low noise temperature, it can be used in cutting-edge fields such as precision measurement, space communication, and quantum radar.

[0003] In recent years, research teams at home and abroad have made some progress in the theoretical and experimental research of this technology. In 2015, researchers at Imperial College used a dielectric microwave resonant cavity to reduce the threshold power consumption of the microwave laser by an order of magnitude, providing an effective technical approach for practical devices. In 2018, British and German research teams respectively demonstrated the feasibility of solid-state microwave lasers in continuous wave mode at room temperature and pressure through experiments. In 2021, Eisenach, Barry, Schloss and others from the Massachusetts Institute of Technology developed a cavity-enhanced microwave readout scheme and achieved 3.2pT·Hz -1 / 2 It can be predicted that microwave maser technology may further improve the sensitivity of magnetic field detection.

[0004] Faced with the development and evolution of wireless receiver miniaturization and intelligent multifunctional application scenarios, the requirements for the detection of extremely weak microwave signals are becoming more and more urgent. It is necessary to explore the development results of new system technologies and break the bottleneck of traditional electromagnetic architecture as an important technical route. Compared with traditional low-temperature microwave lasers and non-solid-state microwave laser technologies, solid-state microwave lasing technology will greatly reduce R&D costs, broaden application scenarios, and realize the miniaturization and micro-miniaturization of wireless receiver systems, providing a new technical path for the development of the next generation of secondary radar receiver systems.

[0005] The size of the existing secondary radar antenna is limited by the limit of metal antennas, and the improvement of system sensitivity has almost reached its limit. With the development of secondary radar systems, higher requirements are placed on the receiving performance of equipment, and many challenges are also faced. (1) Radio terminal equipment is getting smaller and smaller, but the development of antennas does not obey Moore's Law. Its size is strictly limited by the Chu limit. The lower the frequency, the larger the antenna size is required; (2) Electromagnetic field measurement requires highly sensitive and high-precision sensors / receivers, but the disturbance of the electromagnetic field to be measured by metal antenna probes makes it difficult to improve the measurement accuracy. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a secondary radar quantum interrogation receiver to solve the problems of low sensitivity and the like in the prior art.

[0007] The technical solution adopted by the present invention to solve the above problems is:

[0008] A secondary radar quantum interrogation receiver comprises a resonant cavity, a gain medium arranged in the resonant cavity, and a stimulated radiation source arranged in the resonant cavity.

[0009] As a preferred technical solution, the stimulated radiation source is a diamond crystal.

[0010] As a preferred technical solution, the stimulated radiation source is a diamond crystal doped with NV color centers.

[0011] As a preferred technical solution, the gain medium is a dielectric ring.

[0012] As a preferred technical solution, the gain medium is made of a high dielectric constant material.

[0013] As a preferred technical solution, the gain medium is made of strontium titanate, rutile or potassium tantalate.

[0014] As a preferred technical solution, the shape of the resonant cavity is cylindrical.

[0015] As a preferred technical solution, the resonant cavity is made of copper.

[0016] As a preferred technical solution, it also includes a pump source arranged outside the resonant cavity.

[0017] As a preferred technical solution, the pump source is a laser.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention realizes the transmission amplification of microwave signals with an operating frequency of 1090 MHz, meets the measurement indicators of various antenna signals and performs extremely well. Compared with traditional solutions, the volume is drastically reduced and the sensitivity is significantly improved, which has a significant and far-reaching impact in the fields of microwave communications, quantum radar, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a secondary radar quantum interrogation receiver according to the present invention;

[0021] Figure 2 It is a flow chart of building and testing of the present invention.

[0022] Marks and their corresponding names in the accompanying drawings: 1. resonant cavity, 2. gain medium, 3. stimulated radiation source, 4. pump source. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0024] Example 1

[0025] like Figure 1 to Figure 2 As shown, in order to meet the above challenges, the information receiving equipment adopts a solid-state quantum system, which enables the noise floor of the received signal to be reduced by several orders of magnitude. The use of quantum receivers in secondary radar systems is not only expected to break through the sensitivity limit of traditional receivers, but also to get rid of the limitation of antenna size, which helps to meet the requirements of ultra-high sensitivity reception of secondary radar systems.

[0026] The present invention utilizes the development achievements of new system technologies to break the bottleneck of traditional electromagnetic architecture, mainly targeting the problems of ultra-high sensitivity reception of microwave signals by secondary radar systems, system miniaturization and limited antenna size.

[0027] The present invention proposes an L-band secondary radar quantum interrogation receiver based on solid-state microwave technology. The receiving target frequency band of the technology belongs to the L-band interrogator, and the operating frequency is 1090MHz.

[0028] The technical solution adopted by the present invention to solve the above technical problems is: prepare and regulate solid-state spin gain media, systematically design microwave resonant cavities that meet the response frequency, and integrate and optimize the optical path and pump laser. Figure 1 As shown, the implementation path is as follows Figure 2 The flowchart is shown in FIG.

[0029] The present invention proposes an L-band quantum receiver based on solid-state microwave maser. The specific implementation process and test scheme are as follows Figure 2 shown.

[0030] Device parts such as Figure 1 As shown, it includes a resonant cavity part (a resonant cavity 1 containing a copper shell, a dielectric ring (gain medium 2), and a diamond crystal doped with NV color centers), and the diamond crystal doped with NV color centers is a stimulated radiation source 3.

[0031] The resonant cavity includes a base, a cavity wall that can be directly connected to the base through threads, and a piston knob that is connected to the cavity wall through threads; after the piston knob and the cavity wall are installed, the knob can be used to adjust the lifting and lowering of the piston knob to achieve the function of adjusting the frequency. Inside the resonant cavity, there is a bracket fixed to the base and a microwave dielectric material ring (dielectric ring) fixed to the bracket.

[0032] The outermost layer of the resonant cavity mainly used in the present invention is a cylindrical oxygen-free copper cavity with an inner diameter of 42 mm and an inner height of 34 mm, which plays a sealing role. There is a "piston-type" tuning knob at the upper end of the cavity to adjust the resonant cavity TE 01δThe frequency of the mode. There is a polystyrene bracket with a height of 11mm in the center to place a single crystal strontium titanate (STO) ring with an inner diameter of 4.2mm, an outer diameter of 15.04mm, and a height of 11.5mm. The inner and outer surfaces are finely polished, thereby generating an electromagnetic mode in the copper cavity. A gain medium of appropriate size (3mm long, 3mm wide, and 0.5mm thick) is placed in the single crystal STO ring.

[0033] The microwave dielectric material ring and the bracket are stacked and fixed in the cavity to form a whole; the microwave dielectric material is made of high dielectric constant material, such as strontium titanate, and rutile, potassium tantalate and other materials can also be selected; the bracket is made of cross-linked polystyrene plastic, and other low dielectric constant and low microwave loss materials can also be selected.

[0034] The core parameter indicators of the present invention will be introduced in detail below.

[0035] The present invention uses stimulated radiation between the |-1> state and the |0> state of the diamond NV color center to achieve high-gain amplification of microwaves. The dynamic characteristics of the amplification process can be described by the quantum Langevin equation. That is:

[0036]

[0037]

[0038] Where w is the pump rate, which is related to the laser, γ eg Represents the relaxation rate between the |-1> state and the |0> state, which is related to the properties of diamond itself, κ c is the cavity dissipation rate, κ s is the decoherence rate of the spin, g is the coupling strength between the electromagnetic mode and the spin, ω s is the angular frequency of the spin, ω c is the angular frequency of the microwave field.

[0039] is the excited state population operator, is the ground state particle number operator, represents the drop operator of the spin system, Represents the descending operator of the microwave field, with different subscripts Represents fluctuations from different sources.

[0040] Diamond-based microwave amplifiers can achieve stable amplification output after a very short period of time, so the steady-state solution of the above Langevin equation can be obtained. At the same time, using the expectation value instead of the operator, the steady-state equation under the central field approximation can be obtained:

[0041] 0=wN g -γ eg N e+ig(a * S - -S + a)

[0042]

[0043] On this basis, an external driving term (i.e. input microwave) is introduced And in the equation, ω in Rotating the coordinate system for the angular frequency gives:

[0044] 0=wN g -γ eg N e +ig(a * S - -S + a)

[0045]

[0046]

[0047] Where S z =N e -N g , N e +N g =N.κ c is the dissipation rate of the cavity, which consists of two parts: the loss of the cavity itself (κ vac ), due to the loss of coupling with input and output ex .

[0048] After a series of calculations, the relationship between the input microwave and output microwave amplitudes can be obtained from the equation:

[0049]

[0050] where δ s =ω in -ω s , δ c =ω in -ω c , represents the detuning frequency between the input microwave and the spin and cavity.

[0051] When the cavity works in the optimal amplification mode, the frequencies of the spin, cavity, and input signal are consistent, that is, δ s =δ c = 0, and the dissipation of the cavity is mainly caused by the input-input coupling, that is, κ c =κ ex . At this time, the input-output relationship can be simplified to:

[0052]

[0053] The definition of gain is the power ratio of input to output, that is,

[0054] As long as all the parameters in the formula can be estimated, the final gain of the amplifier can be calculated. The following parts are all based on this formula, combining existing file data, existing experimental conditions and other parameters to calculate the gain G.

[0055] First, g represents the coupling between spin and microwave photon, which can be obtained by the following formula:

[0056]

[0057] where γ NV / 2π=2.8033MHz / Gauss, represents the gyromagnetic ratio. μ0 is the vacuum dielectric constant, is the reduced Planck constant, V eff Represents the mode volume. Based on the previous simulation, we can roughly estimate: V eff ≈1.5cm 3 , g≈0.10Hz.

[0058] Next, we calculate κ s , which represents the spin decoherence rate. The diamond relaxation time T2* we currently use is about 300ns, and the spin decoherence rate is calculated according to the following formula:

[0059]

[0060] Then estimate Sz, where S z =N e -N g , N e +N g =N. Here N e and N g Represent the number of particles in the ground state and excited state, respectively, and N represents the total number of spins in these two energy levels. According to the description in the literature (Breeze, J., Salvadori, E., Sathian, J. et al. Continuous-wave room-temperature diamond maser. Nature 555, 493–496 (2018).), S z Can reach 0.1N.

[0061] where N can be estimated based on the size of the diamond:

[0062] Diamond volume: 0.3×0.3×0.05cm3 ;

[0063] Diamond density: 3.51g / cm 3 ;

[0064] Diamond mass: 0.015795g;

[0065] ●Amount of carbon atom substance: 0.00131625 mol = 7.92383 × 1020 atoms;

[0066] ●NV color center concentration: 4.5ppm;

[0067] Number of NV color centers: 3.56572×10 15 indivual.

[0068] Since the required L-band energy level requires the application of a magnetic field, we are only concerned with NV color centers along the direction of the magnetic field, which is only 1 / 4 of the number of NV color centers mentioned above: 8.9143×1014. At the same time, considering the existence of the |+1> state of NV color centers, the |-1> and |0> states actually only account for about 2 / 3, so N≈8.9143×1014×2 / 3≈6×1014. Then S z ≈6×10 13 .

[0069] The final key is to calculate the dissipation rate of the cavity, i.e., κ c The value of . From the formula we can know:

[0070]

[0071] Where Q is the quality factor of the cavity. For the L-band operating frequency, we consider the Q value of the resonant cavity to be 15000. z , g and κ s , we can calculate G≈71.49, that is, G≈18.54dB.

[0072] Through theoretical calculation and simulation analysis, under the conditions of suitable diamond samples, suitable excitation, and suitable cavity, the present invention can achieve a gain of 15dB to 20dB.

[0073] The noise factor is used to measure the size of network noise. The most common definition is the ratio of input to output signal-to-noise ratio, which can be expressed as the following formula:

[0074]

[0075] Among them, S in and S out Represents the power of input and output signals, N in represents input noise, Nout represents the output noise. For an amplifier, the noise figure can be defined as:

[0076]

[0077] in Represents gain, and this definition is completely equivalent to the conventional definition.

[0078] However, for the present invention, since it has both amplification and filtering functions, it is relatively difficult to measure input and output noise. In fact, it is also difficult to measure in reality. We use the tool of noise temperature to calculate the noise factor in reverse. Noise temperature can measure noise power. It is equal to the absolute temperature of a resistor when it gives the same power in the same bandwidth as the noise source. It is expressed as:

[0079]

[0080] Where P represents the available noise power, k is the Boltzmann constant, and Δf represents the bandwidth.

[0081] For the present invention, the internal noise can be converted into the corresponding noise amount introduced at the input end, which is exactly the equivalent noise temperature T noise The equivalent noise temperature and noise coefficient can be equivalently converted, and their numerical relationship is expressed as:

[0082] T noise =(F-1)·T0

[0083] Where T0≈293K, represents the physical temperature of the environment. In addition, the noise temperature of the amplifier can be expressed by the following formula:

[0084]

[0085] This formula is derived from the international test standard for microwave laser noise temperature released in 2008. The physical meaning and value of each parameter are listed in Table 1:

[0086] Table 1 Physical meaning of each parameter and corresponding value (noise coefficient)

[0087]

[0088]

[0089] The gain here is based on the estimation, and the lower limit of the gain value is selected. Determined by the properties of the resonant cavity, it can be calculated using the following formula:

[0090]

[0091] According to the experimental results data obtained, the load quality factor QL≈1800 in the working state and the quality factor Q under critical coupling are C ≈2500, estimated by calculation

[0092] According to the discussion in Nature 555,493–496 (2018), the polarization degree of the laser on the spin can be calculated. Substituting the data in the table into the formula, it can be calculated that when the resonant frequency is in the L band, the noise temperature Tnoise is about 45K (the noise temperature is not sensitive to frequency). Substituting the formula:

[0093] T moise =(F-1)·T0

[0094] The calculation shows that F≈1.154, which is converted into dB, and then F≈0.622dB, so the noise coefficient of the present invention is less than 1dB.

[0095] For the microwave lasing technology used in the present invention, the sensitivity is mainly restricted by the influence of Johnson-Nyquist noise (including thermal noise and quantum noise). The higher the temperature, the more dominant the thermal noise is. In fact, for microwave signals below GHz frequency, even at liquid helium temperature (4.2K), Johnson-Nyquist noise is still dominated by thermal noise, and the power definition of thermal noise is as follows:

[0096]

[0097] where k B is the Boltzmann constant and T is the temperature.

[0098] According to the previous calculation, the noise temperature of our system is about 45K (not sensitive to frequency). Therefore, our amplifier can be regarded as a noise source, and its noise power spectrum density is calculated as:

[0099] The bandwidth of the present invention is 1MHz, and the actual noise power is -122dBm. Under the influence of Johnson-Nyquist noise, the basic noise level of the present invention at 1MHz is -122dBm. If a -107dBm signal is input, the requirement of a signal-to-noise ratio of 15dB can be met.

[0100] The minimum detectable signal of the present invention under 1 MHz instantaneous bandwidth is -107 dBm signal, and the output SNR is greater than 15 dB.

[0101] Example 2

[0102] like Figure 1 to Figure 2 As shown, as a further optimization of Example 1, based on Example 1, this embodiment also includes the following technical features:

[0103] In the present invention, a solid spin system of nitrogen-vacancy color center (NV color center) in diamond is used in combination with a novel resonant cavity structure and an appropriate external magnetic field to achieve a microwave operating frequency of 1090 MHz in the L band.

[0104] In the present invention, the principle of microwave lasing technology utilizes the population inversion between the |0> state and the |±1> state in the NV color center spin triplet state, and generates stimulated radiation under the action of a microwave signal of the corresponding frequency, thereby realizing microwave amplification. Under the excitation of a 532nm continuous laser pump source, the electron population of the sub-energy level |0> of the triplet ground state can be much higher than the sub-energy level |±1>, that is, light-induced spin polarization is generated, and the polarization rate is about 80%. Under the action of an external magnetic field, the originally degenerate sub-energy level |±1> is split due to the Zeeman effect, so that the energy of the sub-energy level |-1> begins to be lower than |0>. Under an appropriate external magnetic field, |0> and |-1> construct a two-level system with electron population inversion characteristics, and the energy level difference can be adjusted to an operating frequency of 1090MHz in the L band.

[0105] In the present invention, a microwave mode with an operating frequency of 1090 MHz can be generated by designing a microwave dielectric resonant cavity, so that the frequency of the resonant cavity is equal to the energy level difference of the two-level system of |0> and |-1> in the NV color center. When microwave photons of the corresponding operating frequency interact with the system, electrons transition from |0> to |-1> and radiate microwave photons coherent with the microwave signal, that is, stimulated radiation occurs, microwave lasing is generated, and microwave signals are amplified.

[0106] In the resonant cavity described in the present invention, the cavity includes a base, a shell (top and side walls are integrated), a knob, and a microwave dielectric ring.

[0107] In the resonant cavity described in the present invention, the base, the housing and the knob are made of high-purity metal.

[0108] In the resonant cavity described in the present invention, the knob and the housing are matched with each other by threads, and the knob can be moved up and down by adjusting the threads.

[0109] In the resonant cavity described in the present invention, the base includes a support hole and a microwave cable hole.

[0110] In the resonant cavity described in the present invention, the shell is cylindrical, the side wall and the top are integrated, and there is a small hole in the side wall for laser incidence.

[0111] In the resonant cavity described in the present invention, the bracket is made of plastic material with low dielectric constant and low microwave loss.

[0112] In the resonant cavity described in the present invention, the microwave dielectric ring is made of a high dielectric constant material and is fixed by the bracket.

[0113] The present invention mainly focuses on the interrogator in the secondary radar, a small-size, low-noise, and extremely good antenna performance quantum receiver based on solid-state microwave maser.

[0114] In the present invention, the device is divided into a pump module and a resonant cavity module.

[0115] In the present invention, the pump source of the pump module is a high-power laser.

[0116] In the present invention, the resonant cavity module comprises a resonant cavity wall, a gain medium, a dielectric resonator, a bracket, and an antenna.

[0117] In the present invention, the resonant cavity wall includes a base, a shell (top and side walls are integrated), and a knob. The knob and the shell are matched with each other by threads, and the knob can be moved up and down by adjusting the threads.

[0118] In the present invention, the cavity wall of the resonance cavity is made of high-purity metal.

[0119] In the present invention, the dielectric resonator is composed of one or more microwave dielectric rings, and the material of the dielectric ring is a high dielectric constant material.

[0120] In the present invention, the antenna is inserted into the base of the microwave cavity to serve as a microwave input port and a microwave output port.

[0121] In the present invention, the bracket is made of low dielectric constant and low microwave loss plastic and is used to fix the dielectric resonator.

[0122] In the present invention, the gain medium is a diamond crystal doped with NV color centers.

[0123] As described above, the present invention can be preferably implemented.

[0124] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

[0125] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A secondary radar quantum interrogation receiver, characterized in that: It comprises a resonant cavity (1), a gain medium (2) arranged in the resonant cavity (1), and a stimulated radiation source (3) arranged in the resonant cavity (1).

2. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The source of stimulated radiation is a diamond crystal.

3. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The source of stimulated emission is NV color center-doped diamond crystal.

4. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The gain medium (2) is a dielectric ring.

5. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The gain medium (2) is made of a high dielectric constant material.

6. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The gain medium (2) is made of strontium titanate, rutile or potassium tantalate.

7. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The resonant cavity (1) is cylindrical in shape.

8. A secondary radar quantum interrogation receiver according to claim 1, characterized in that: The resonant cavity (1) is made of copper.

9. A secondary radar quantum interrogation receiver according to any one of claims 1 to 8, characterized in that: It also includes a pump source (4) arranged outside the resonant cavity (1).

10. A secondary radar quantum interrogation receiver according to claim 9, characterized in that: The pump source (4) is a laser.

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