Method and apparatus for generating broadband microwave signals based on microwave photonics technology

Abstract

This invention discloses a method for generating broadband microwave signals based on microwave photonics technology. A reference microwave signal and an excitation microwave signal are simultaneously passed through a 90° microwave bridge to obtain two orthogonal microwave signals. These two orthogonal microwave signals are then used to perform carrier-suppressed single-sideband modulation on an optical carrier using a dual parallel intensity modulator. The generated modulated optical signal is then optically amplified and filtered before photoelectric conversion to generate a frequency-converted microwave signal. This frequency-converted microwave signal is split into two paths: one is used as the system output, and the other is electrically amplified and filtered before being fed back to the 90° microwave bridge, thus forming a closed frequency conversion loop. After multiple frequency conversions, the system outputs an ultra-wide bandwidth microwave signal. This invention also discloses a broadband microwave signal generation device based on microwave photonics technology. Compared with existing technologies, this invention can generate ultra-wide bandwidth microwave signals in different frequency bands and multiple formats.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of broadband microwave signal generation method and device based on microwave photon technology, belong to microwave photon technical field. BACKGROUND

[0002] As a kind of sensor that can work all day and all weather, high-resolution microwave radar has extensive and urgent demand in applications such as automatic driving, target identification, safety monitoring. Broadband microwave signal is one of the necessary conditions for radar to achieve high resolution. However, even the most advanced electronic technology is difficult to break through the bandwidth bottleneck to produce microwave signals with ultra-wide bandwidth. On the other hand, with the electromagnetic space spectrum becoming more and more complex, in order to improve the radar detection reliability and anti-interference, different frequency bands, different signals of different systems are often used for detection, so the microwave signal generation system also needs to have certain tunability and reconfigurability, which also poses a great challenge to electronic technology.

[0003] Microwave photonics technology with large bandwidth, low transmission loss, anti-electromagnetic interference and other characteristics is expected to break through the bottleneck of electronic technology and produce ultra-large bandwidth and reconfigurable microwave signals. At present, the microwave photonics signal generation schemes mainly include frequency-time mapping, swept laser, optical digital-to-analog conversion, microwave photonics frequency multiplication, and cyclic frequency shift (see [Pan S, Zhang Y. Microwave photonic radars. Journal of Lightwave technology, 2020, 38(19): 5450-5484] [Zhang Y, Liu C, Zhang Y, et al. Multi-functional radar waveform generation based on optical frequency-time stitching method. Journal of Lightwave Technology, 2021, 39(2): 458-464]), and with the help of these technologies, a signal generation system with large bandwidth and certain reconfigurability can be realized. However, the time-bandwidth product of the signal generated by frequency-time mapping is very small, which is not suitable for long-distance detection; the linearity of the swept laser is poor, and the coherence is poor; the optical digital-to-analog conversion is limited by the effective number of bits, and the signal generated by the radar system has the problem of poor signal-to-noise ratio; the microwave photonics frequency multiplication scheme is relatively simple, but the bandwidth of the generated signal depends on the bandwidth of the microwave driving signal; the cyclic frequency shift can generate a very large bandwidth microwave signal, but the generated signal is greatly affected by the phase noise of the laser (see [Turner LD, Weber K P, Hawthorn C J, et al. Frequency noise characterisation of narrow linewidth diode lasers. Optics communications, 2002, 201(4-6): 391-397]). Therefore, it is of great significance to study a high-quality tunable broadband microwave signal generation scheme that can break through the bottleneck of electronic bandwidth, which can improve the performance of radar and other applications. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a wideband microwave signal generation method based on microwave photonics technology, which can generate ultra-large bandwidth microwave signals of different frequency bands and multiple types.

[0005] The present application specifically adopts the following technical solutions to solve the above technical problems:

[0006] A method for generating broadband microwave signals based on microwave photonics technology involves simultaneously passing a reference microwave signal and an excitation microwave signal through a 90° microwave bridge to obtain two orthogonal microwave signals. These two orthogonal microwave signals are then used to perform carrier-suppressed single-sideband modulation on an optical carrier using a dual parallel intensity modulator. The generated modulated optical signal is then optically amplified and filtered before photoelectric conversion to generate a frequency-converted microwave signal. This frequency-converted microwave signal is split into two paths: one is used as the system output, and the other is electrically amplified and filtered before being fed back to the 90° microwave bridge to form a closed frequency-converting loop. The excitation microwave signal is a pulse signal, and the reference microwave signal is either a continuous wave signal or a pulse signal with a period equal to the delay of the frequency-converting loop. The gain of the frequency-converting loop is set to 1, and condition T is satisfied. r ≥NT L ≥NT pw After multiple frequency conversions, the system outputs an ultra-wide bandwidth microwave signal; among which, T L For frequency converter loop delay, T pw and T r These are the pulse width and period of the excitation microwave signal, respectively, and N is the number of frequency conversions determined by the cutoff frequencies of the optical filter and the electrical filter in the frequency conversion loop.

[0007] Furthermore, by controlling the same or different ports of the reference microwave signal and the excitation microwave signal input to the 90° microwave bridge, an ultra-wide bandwidth microwave signal with a center frequency that decreases or increases over time can be generated.

[0008] Preferably, both the reference microwave signal and the excitation microwave signal are single-frequency signals, and the ultra-wide bandwidth microwave signal is a step-frequency signal.

[0009] Preferably, the reference microwave signal frequency is a single-frequency signal, the excitation microwave signal is a scanning frequency, and the ultra-wide bandwidth microwave signal is a step-modulated signal.

[0010] Preferably, the reference microwave signal is a scanning frequency signal; if the excitation microwave signal is a single-frequency signal, the reference microwave signal and the excitation microwave signal are input through different ports of a 90° microwave bridge; if both the reference microwave signal and the excitation microwave signal are scanning frequencies with modulation slopes of k1 and k2 respectively, when these two signals are input through different ports of a 90° microwave bridge, k1 ≠ –k2 must be satisfied, and when these two signals are input through the same port of a 90° microwave bridge, k1 ≠ k2 must be satisfied; the ultra-wide bandwidth microwave signal is a multi-chirped signal with a center frequency that varies with time.

[0011] Based on the same inventive concept, the following technical solutions can also be obtained:

[0012] A broadband microwave signal generation device based on microwave photonics technology, comprising:

[0013] The microwave photonic frequency conversion module is used to simultaneously pass a reference microwave signal and an excitation microwave signal through a 90° microwave bridge to obtain two orthogonal microwave signals. The excitation microwave signal is a pulse signal, and the reference microwave signal is a continuous wave signal or a pulse signal with a period equal to the frequency conversion loop delay. These two orthogonal microwave signals are used to perform carrier-suppressed single-sideband modulation on the optical carrier through dual parallel intensity modulators. The generated modulated optical signal is then optically amplified and optically filtered before photoelectric conversion to generate a frequency-converted microwave signal.

[0014] The microwave feedback module splits the frequency-converted microwave signal into two paths: one path serves as the system output, and the other path, after electrical amplification and filtering, is fed back to the 90° microwave bridge to form a closed frequency conversion loop. The gain of the frequency conversion loop is 1, and it satisfies condition T. r ≥NT L ≥NT pw After multiple frequency conversions, the system outputs an ultra-wide bandwidth microwave signal; among which, T L For frequency converter loop delay, T pw and T r These are the pulse width and period of the excitation microwave signal, respectively, and N is the number of frequency conversions determined by the cutoff frequencies of the optical filter and the electrical filter in the frequency conversion loop.

[0015] Preferably, the reference microwave signal and the excitation microwave signal are input to the same / different ports of the 90° microwave bridge, and the system output is an ultra-wide bandwidth microwave signal with a center frequency that decreases / increases over time.

[0016] Preferably, both the reference microwave signal and the excitation microwave signal are single-frequency signals, and the ultra-wide bandwidth microwave signal is a step-frequency signal.

[0017] Preferably, the reference microwave signal frequency is a single-frequency signal, the excitation microwave signal is a scanning frequency, and the ultra-wide bandwidth microwave signal is a step-modulated signal.

[0018] Preferably, the reference microwave signal is a scanning frequency signal; if the excitation microwave signal is a single-frequency signal, the reference microwave signal and the excitation microwave signal are input through different ports of a 90° microwave bridge; if both the reference microwave signal and the excitation microwave signal are scanning frequencies with modulation slopes of k1 and k2 respectively, when these two signals are input through different ports of a 90° microwave bridge, k1 ≠ –k2 must be satisfied, and when these two signals are input through the same port of a 90° microwave bridge, k1 ≠ k2 must be satisfied; the ultra-wide bandwidth microwave signal is a multi-chirped signal with a center frequency that varies with time.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] 1. This invention uses cyclic microwave photonic frequency conversion technology to extend the bandwidth of microwave signals, and the generated signals are not affected by laser phase noise.

[0021] 2. This invention breaks through the limitations of traditional electronic technology on system bandwidth, and the maximum frequency coverage of the generated microwave signal can be N times that of the reference microwave signal.

[0022] 3. This invention can generate tunable broadband microwave signals of different frequency bands and multiple standards through simple control. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the structural principle of the broadband microwave signal generating device of the present invention;

[0024] Figure 2 This is a schematic diagram of a dual parallel intensity modulator.

[0025] Figure 3 This is a schematic diagram of the output signal spectrum of a dual parallel intensity modulator.

[0026] Figure 4 The time-frequency diagram of the step frequency signal generated by the system;

[0027] Figure 5 The time-frequency diagram of the stepped frequency modulation signal generated by the system;

[0028] Figure 6 The time-frequency diagram shows the multi-chirped signals generated by the system. Detailed Implementation

[0029] To address the shortcomings of existing technologies, this invention proposes a broadband microwave signal generation method based on microwave photonics technology, as detailed below:

[0030] The reference microwave signal and the excitation microwave signal are simultaneously passed through a 90° microwave bridge to obtain two orthogonal microwave signals. These two orthogonal microwave signals are then used to perform carrier-suppressed single-sideband modulation on the optical carrier using a dual parallel intensity modulator. The generated modulated optical signal is then optically amplified and filtered before photoelectric conversion to generate a frequency-converted microwave signal. This frequency-converted microwave signal is split into two paths: one is used as the system output, and the other is electrically amplified and filtered before being fed back to the 90° microwave bridge to form a closed frequency conversion loop. The excitation microwave signal is a pulse signal, and the reference microwave signal is either a continuous wave signal or a pulse signal with a period equal to the frequency conversion loop delay. The gain of the frequency conversion loop is set to 1, and condition T is satisfied. r ≥NT L ≥NT pw After multiple frequency conversions, the system outputs an ultra-wide bandwidth microwave signal; among which, T L For frequency converter loop delay, T pw and Tr These are the pulse width and period of the excitation microwave signal, respectively, and N is the number of frequency conversions determined by the cutoff frequencies of the optical filter and the electrical filter in the frequency conversion loop.

[0031] Furthermore, by controlling the same or different ports of the reference microwave signal and the excitation microwave signal input to the 90° microwave bridge, an ultra-wide bandwidth microwave signal with a center frequency that decreases or increases over time can be generated.

[0032] Preferably, both the reference microwave signal and the excitation microwave signal are single-frequency signals, and the ultra-wide bandwidth microwave signal is a step-frequency signal.

[0033] Preferably, the reference microwave signal frequency is a single-frequency signal, the excitation microwave signal is a scanning frequency, and the ultra-wide bandwidth microwave signal is a step-modulated signal.

[0034] Preferably, the reference microwave signal is a scanning frequency signal; if the excitation microwave signal is a single-frequency signal, the reference microwave signal and the excitation microwave signal are input through different ports of a 90° microwave bridge; if both the reference microwave signal and the excitation microwave signal are scanning frequencies with modulation slopes of k1 and k2 respectively, when these two signals are input through different ports of a 90° microwave bridge, k1 ≠ –k2 must be satisfied, and when these two signals are input through the same port of a 90° microwave bridge, k1 ≠ k2 must be satisfied; the ultra-wide bandwidth microwave signal is a multi-chirped signal with a center frequency that varies with time.

[0035] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings:

[0036] The broadband microwave signal generating device of the present invention, such as Figure 1 As shown, it includes:

[0037] The microwave photonic frequency conversion module consists of a laser, a dual parallel intensity modulator, an optical amplifier, an optical filter, a photodetector, a 90° microwave bridge, and a coupler. It is used to simultaneously pass a reference microwave signal and an excitation microwave signal through a 90° microwave bridge to obtain two orthogonal microwave signals. The excitation microwave signal is a pulse signal, and the reference microwave signal is a continuous wave signal or a pulse signal with a period equal to the frequency conversion loop delay. These two orthogonal microwave signals are used to perform carrier-suppressed single-sideband modulation on the optical carrier through the dual parallel intensity modulator. The resulting modulated optical signal is then optically amplified and filtered before photoelectric conversion to generate the frequency-converted microwave signal.

[0038] The microwave feedback module, composed of a power divider, an amplifier, and a filter, splits the frequency-converted microwave signal into two paths. One path serves as the system output, while the other, after amplification and filtering, is fed back to the 90° microwave bridge, forming a closed frequency conversion loop. The gain of the frequency conversion loop is 1, and condition T is satisfied.r ≥NT L ≥NT pw After multiple frequency conversions, the system outputs an ultra-wide bandwidth microwave signal; among which, T L For frequency converter loop delay, T pw and T r These are the pulse width and period of the excitation microwave signal, respectively, and N is the number of frequency conversions determined by the cutoff frequencies of the optical filter and the electrical filter in the frequency conversion loop.

[0039] To facilitate public understanding, the principles of this invention will be further explained in detail below:

[0040] Assume the normalized expression for the reference microwave signal is s r =cos(2πf) r t), where f r The reference microwave signal frequency is used; the normalized expression for the excitation microwave signal is s. d =cos(2πf) d t), where f d The frequency of the excitation microwave signal. When two microwave signals are input through the same port of a 90° microwave bridge, the two output signals of the 90° microwave bridge are respectively expressed as s1∝cos(2πf r t+π / 2)+cos(2πf d t+π / 2) and s2∝cos(2πf r t)+cos(2πf d When two microwave signals are input through different ports of a 90° microwave bridge, the expressions for the two output ports of the 90° microwave bridge are s1∝cos(2πf). r t)+cos(2πf d t+π / 2) and s2∝cos(2πf r t+π / 2)+cos(2πf d t). The two outputs of the 90° microwave bridge are fed to a dual parallel intensity modulator to modulate the optical carrier generated by the laser. For example... Figure 2 As shown, the dual parallel intensity modulator consists of two sub-intensity modulators and one main intensity modulator. The two outputs of the 90° microwave bridge are respectively applied to the two sub-intensity modulators of the dual parallel intensity modulator. Both sub-intensity modulators operate at the minimum bias point, and the main intensity modulator operates at the quadrature bias point. Therefore, the dual parallel intensity modulator will output a modulated optical signal with carrier-suppressed single-sideband characteristics.

[0041] Let the laser signal be:

[0042]

[0043] Among them, EL and f L These represent the intensity and frequency of the laser signal, respectively. This refers to the phase noise of the laser. When the reference microwave signal and the excitation microwave signal are input through the same port of a 90° microwave bridge, the two sidebands of the dual parallel intensity modulator output are distributed on the same side of the laser carrier, as shown below. Figure 3 As shown in (a), the system is in down-conversion mode at this time; conversely, when the reference microwave signal and the excitation microwave signal are input through different ports of the 90° microwave bridge, the dual parallel intensity modulator outputs two sidebands distributed on both sides of the laser carrier, as shown in (a). Figure 3 As shown in (b) in the figure, the system is in the up-conversion state at this time.

[0044] When operating in down-conversion mode, the output signal expression of the dual parallel intensity modulator is:

[0045]

[0046] When the system is operating in up-conversion mode, the output signal expression of the dual parallel intensity modulator is:

[0047]

[0048] Where Δt is the time difference between the upper and lower arms.

[0049] The output of the dual parallel intensity modulator, after passing through an optical amplifier and a filter, enters the beat frequency output of the photodetector as a frequency-converted signal.

[0050] The system is operating in down-conversion mode (4)

[0051] or

[0052] The system is operating in up-conversion mode (5)

[0053] Therefore, it can be seen that the frequency of the photodetector's output signal increases or decreases by f compared to the input excitation signal. r Additionally, it should be noted that the frequency conversion signal also contains phase jitter caused by laser phase noise. In this scheme, since the two sub-intensity modulators are integrated together, Δt≈0, so the phase jitter can be coherently canceled.

[0054] The output of the photodetector is split into two paths by a power divider. One path serves as the system output, while the other, after passing through an electrical amplifier and filter, is fed back to a 90° microwave bridge via a coupler, forming a closed-loop frequency conversion circuit. The gains of the optical amplifier and electrical amplifier are adjusted to make the gain of the frequency conversion loop equal to 1. This allows the system to perform multiple frequency conversions on the microwave signal, thus broadening the signal bandwidth. The system output signal can be expressed as:

[0055]

[0056] Where N is the number of frequency conversions, which is controlled by the cutoff frequencies of the optical filter and the electrical filter, and T... L For the delay of the frequency converter loop, T pw To excite the microwave signal pulse width, φ i Let be the starting phase of the i-th sub-pulse. Additionally, considering practical applications, to avoid crosstalk between signals, condition T must also be satisfied. r ≥NT L and T L ≥T pw T r The reference microwave signal is the period of the excitation microwave signal. Unlike the excitation microwave signal, which must be a pulse signal, the reference microwave signal can be a continuous wave signal or a pulse signal. It is important to note that when the reference microwave signal is a pulse signal, its period must be the same as that of the frequency conversion loop.

[0057] Taking the above frequency conversion as an example, the excitation microwave signal and the reference microwave signal are input through different ports of a 90° microwave bridge. If f d and f r If both are fixed frequencies, then the following will be produced: Figure 4 The step frequency signal shown; if f d f is the scanning frequency. r If the frequency is fixed, then the following will be generated: Figure 5 The step frequency modulation signal shown; f can also be used as a step frequency modulation signal. r Set the scan frequency to produce, for example: Figure 6 The multi-chirped signal is shown.

[0058] When f r When the scanning frequency is set, if the excitation microwave signal frequency is a single frequency, the two microwave signals need to be input through different ports of the 90° microwave bridge; if the reference microwave signal and the excitation microwave signal are scanning frequencies and the frequency modulation slopes are k1 and k2 respectively, then when the two signals are input through different ports of the 90° microwave bridge, k1≠–k2 must be satisfied, and when the two signals are input through the same port of the 90° microwave bridge, k1≠k2 must be satisfied.

[0059] Thus, it can be seen that the device has the capability to generate various signal formats, including stepped frequency, stepped frequency modulation, and multi-chirped signals, without being affected by laser phase noise. Furthermore, the system also possesses a certain degree of tunability; for example, the frequency step interval can be set by adjusting the frequency of the reference microwave signal, the signal duration can be set by adjusting the loop delay, and the signal bandwidth can be set by adjusting the cutoff frequencies of the optical and electrical filters.

Claims

1. A method for generating a wideband microwave signal based on microwave photonics technology, characterized in that: The reference microwave signal and the excitation microwave signal pass through a 90° microwave bridge simultaneously to obtain two orthogonal microwave signals; the two orthogonal microwave signals pass through a double parallel intensity modulator to perform carrier-suppressed single sideband modulation on an optical carrier; the generated modulated optical signal is optically amplified and filtered, and then photoelectrically converted to generate a frequency conversion microwave signal; The frequency conversion microwave signal is divided into two paths, one of which is used as a system output, and the other of which is fed back to the 90° microwave bridge after being electrically amplified and filtered to form a closed frequency conversion loop; the excitation microwave signal is a pulse signal, and the reference microwave signal is a continuous wave signal or a pulse signal with a period equal to the delay of the frequency conversion loop; Let the gain of the frequency conversion loop be 1, and satisfy the condition T r ≥ NT L ≥ NT pw , the system output after multiple frequency conversion of ultra-wide bandwidth microwave signal; wherein, T L is the delay of the frequency conversion loop, T r and T pw are the period and pulse width of the excitation microwave signal respectively, N is the frequency conversion times determined by the cut-off frequency of the optical filter and the electrical filter in the frequency conversion loop.

2. The method of claim 1, wherein the microwave photonics technology-based broadband microwave signal generation method is characterized by: The same or different ports of the reference microwave signal and the excitation microwave signal input the 90° microwave bridge to generate an ultra-wideband microwave signal with a center frequency decreasing or increasing over time.

3. The broadband microwave signal generation method based on microwave photonics technology as described in claim 1, characterized in that: The reference microwave signal and the excitation microwave signal are both single-frequency signals, and the ultra-wideband microwave signal is a step frequency signal. 4.The method of claim 1, wherein the microwave photonics technology is used to generate a wideband microwave signal. The reference microwave signal is a single-frequency signal, and the excitation microwave signal is a scanning frequency, and the ultra-wideband microwave signal is a step frequency signal. 5.The method of claim 1, wherein the method further comprises: generating a microwave signal with a frequency of 1.5 GHz to 2.5 GHz by using the microwave photonics technology. The reference microwave signal is a scanning frequency signal; if the excitation microwave signal is a single frequency signal, the reference microwave signal and the excitation microwave signal are input through different ports of a 90° microwave bridge; if the reference microwave signal and the excitation microwave signal are both scanning frequency signals and the frequency modulation slopes are respectively k 1 and k 2, when the two signals are input through different ports of a 90° microwave bridge, the following condition needs to be met k 1≠– k 2, when the two signals are input through the same port of a 90° microwave bridge, the following condition needs to be met k 1≠ k 2; the ultra-wideband microwave signal is a multi-chirp signal with a time-varying center frequency.

6. A broadband microwave signal generation device based on microwave photonics technology, characterized in that, The system comprises: A microwave photon frequency conversion module is configured to pass a reference microwave signal and an excitation microwave signal through a 90° microwave bridge simultaneously to obtain two orthogonal microwave signals, the excitation microwave signal is a pulse signal, and the reference microwave signal is a continuous wave signal or a pulse signal with a period equal to the delay of the frequency conversion loop; the two orthogonal microwave signals pass through a double parallel intensity modulator to perform carrier-suppressed single sideband modulation on an optical carrier; the generated modulated optical signal is optically amplified and filtered, and then photoelectrically converted to generate a frequency conversion microwave signal; A microwave feedback module is used to divide the variable frequency microwave signal into two paths, one of which is used as the system output, and the other is fed back to the 90° microwave bridge after being electrically amplified and electrically filtered, thereby forming a closed variable frequency loop; the gain of the variable frequency loop is 1, and the condition T r ≥ NT L ≥ NT pw The system output is an ultra-wideband microwave signal after multiple frequency conversions; wherein, T L is the delay of the variable frequency loop, T r and T pw are the period and pulse width of the excitation microwave signal, respectively, N is the frequency conversion number determined by the cut-off frequencies of the optical filter and the electrical filter in the variable frequency loop.

7. The microwave photonic technology based broadband microwave signal generation apparatus of claim 6, wherein, The same / different ports of the reference microwave signal and the excitation microwave signal input the 90° microwave bridge, and the system output is an ultra-wideband microwave signal with a center frequency decreasing / increasing over time.

8. The broadband microwave signal generation device based on microwave photonic technology according to claim 6, wherein, The reference microwave signal and the excitation microwave signal are both single-frequency signals, and the ultra-wideband microwave signal is a step frequency signal.

9. The microwave photonic technology based broadband microwave signal generation apparatus of claim 6, wherein, The reference microwave signal is a single-frequency signal, and the excitation microwave signal is a scanning frequency, and the ultra-wideband microwave signal is a step frequency signal.

10. The broadband microwave signal generation device based on microwave photonic technology according to claim 6, wherein, The reference microwave signal is a scanning frequency signal; if the excitation microwave signal is a single frequency signal, the reference microwave signal and the excitation microwave signal are input through different ports of a 90° microwave bridge; if the reference microwave signal and the excitation microwave signal are both scanning frequency signals and the frequency modulation slopes are respectively k 1 and k 2, when the two signals are input through different ports of a 90° microwave bridge, the following condition needs to be met k 1≠– k 2, when the two signals are input through the same port of a 90° microwave bridge, the following condition needs to be met k 1≠ k 2; the ultra-wideband microwave signal is a multi-chirp signal with a time-varying center frequency.

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