Microwave photon true delay beamforming and spatial filtering control method

Abstract

The invention discloses a microwave photon true delay beamforming and spatial filtering control method, and relates to the technical field of microwaves and the field of optical communication. The method is shown in the figure 1 of the specification, and comprises a receiving antenna, a low noise amplifier, a directly modulated laser, an adjustable optical delay line, an adjustable phase shifter array, an adjustable optical attenuator, a wavelength division multiplexer and a photoelectric detector. An incident signal is modulated on an optical carrier through a directly modulated laser, true delay beamforming is carried out on the modulated optical signal by using a true delay network, analog domain weighting is carried out on the optical signal after true delay beamforming through a phase shift attenuation network, multiple paths of optical signals are combined through a wavelength division multiplexer, and then the optical signal is transmitted to the optical carrier. And an electric signal after true delay beamforming and spatial filtering is obtained through a photoelectric detector. According to the invention, true delay beamforming and spatial filtering can be simultaneously carried out on signals on one system by ingeniously controlling the parameters of the true delay network and the phase shift attenuation network, and the system is high in working frequency band, large in instantaneous bandwidth and high in tuning precision.

Description

Technical Field

[0001] The present invention relates to the fields of microwave technology and optical communication, and mainly relates to microwave photonic true time delay beamforming technology and spatial domain filtering technology. Background Art

[0002] Anti-jamming adaptive array antennas have become a research hotspot in the new generation of radio anti-jamming fields due to their outstanding advantages such as high spatial resolution, strong interference suppression ability, controllable signal gain, and the ability to adaptively achieve spatial pattern control, attracting the attention of many research institutions at home and abroad; true time delay beamforming and spatial domain anti-jamming technology is the core research technology of adaptive array antennas. Combining adaptive signal processing with intelligent antenna arrays, it has efficient spatial domain filtering characteristics.

[0003] Regarding the electrical domain adaptive spatial domain anti-jamming beamforming technology, there has been in-depth research. However, due to the narrow working frequency band of electrical domain technology, it limits the working frequency band and instantaneous bandwidth of electrical domain adaptive spatial domain anti-jamming beamforming. Moreover, electrical domain solutions have disadvantages such as electromagnetic interference, high power consumption, and large volume.

[0004] True time delay technology uses a tunable optical delay line to replace the electrical phase shifter to achieve beamforming, applying variable phase shifts across the entire signal spectrum, thereby eliminating the beam tilt phenomenon generated when the traditional electrical phase shifter performs phase shifting on broadband signals. And by changing the delay amounts of each delay unit, the change of any beam pointing can be realized, which makes it a key technology for broadband phased array antennas.

[0005] "A Reconfigurable Optically Controlled Phased Array Radar Receiver Based on Optical Switching" uses an optical delay line plus an optical attenuator to form a true time delay network. While achieving true time delay beamforming of multi-main lobe broadband signals, it uses the optical attenuator to reduce the sidelobe level and decrease the main lobe width. However, this only realizes the true time delay beamforming of array signals, and the suppression degree of interference signals incident together with the desired signal is limited. Summary of the Invention

[0005] In order to solve the problems existing in the background art, the present invention proposes an optical domain true time delay beamforming and spatial domain filtering control method. This method can achieve true time delay beamforming and spatial domain filtering of high-frequency band and large-bandwidth signals only by using an optical delay line, an optical phase shifter module, and an optical attenuator, and has advantages such as simple structure, high tuning accuracy, and strong anti-electromagnetic interference ability.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows: The device includes N receiving antennas, N low-noise amplifiers LNA, N directly modulated lasers DML with different wavelengths, N variable optical delay lines VODL, an adjustable phase shifter array PSA, N variable optical attenuators VOA, an N-channel wavelength division multiplexer WDM corresponding to N wavelength light sources, and a photodetector PD. The electrical signals received by the N antennas are amplified by the low-noise amplifier LNA and then loaded onto the directly modulated laser DML. The N signals are modulated onto the optical carriers of N wavelengths by direct modulation. The N optical signals first achieve true time delay through the true time delay array composed of variable optical fiber delay lines VODL, and then achieve analog domain weighting through the phase shift attenuation network composed of the adjustable phase shifter array and the variable optical attenuator VOA. Subsequently, they are combined by the N-channel WDM and the optical power is adjusted using an optical attenuator. Finally, they are input into the PD to be converted into electrical signals. By adjusting the optical delay amount, true time delay beamforming at any angle can be achieved. The delay amount is the time delay difference between each array element introduced by the signal incident angle. By adjusting the phase shift amount and optical attenuation amount of the phase shift attenuation network, spatial domain filtering can be achieved. The weighting vector is obtained through a filtering algorithm and then split into the form of amplitude and phase, that is, the signal amplitude is changed by the attenuator, and the phase of the microwave signal modulated on the optical carrier is changed by the adjustable phase shifter array.

[0007] The variable optical delay line VODL described above is composed of optical fibers and has the advantages of low loss, high tuning accuracy, and strong anti-electromagnetic interference ability. The optical signal loaded with the useful signal compensates for the phase difference caused by the arrival time difference in the required direction of the signal through the variable optical delay line, and no beam tilt will be formed. By adjusting the optical delay amount, the beam pointing at any angle can be achieved.

[0008] When the optical signal passes through the phase shift attenuation network, the adjustable optical phase shifter array is used to phase shift the signal after true time delay, and then the variable optical attenuator is used to control the amplitude of the received signal, so as to perform analog domain weighting to achieve spatial domain filtering. In the example of this solution, the adjustable optical delay line is used to form the adjustable optical phase shifter array PSA, but the adjustable optical phase shifter array is not limited to being composed of optical delay lines, and can also be composed of phase shift devices such as phase modulators PM;

[0009] When the present invention is working, it includes the following steps: (1) The N electrical signals received by the N receiving antennas are amplified by the low-noise amplifier LNA and then loaded onto the N directly modulated lasers DML with different wavelength optical carriers. (2) The modulated optical signal is transmitted to the optical delay module through optical fibers. In the optical domain, the true time delay network composed of the variable optical delay line array is used to control the delay of the modulated optical signal. The delay amount is the time delay difference between each array element introduced by the signal incident angle. The signal delays received by each antenna are matched and accurately aligned in the time domain, so that the desired signal is aligned with the normal direction to achieve true time delay beamforming. (4) After implementing true-time-delay beamforming in the optical domain, continue to perform weighting on the signal after true-time-delay beamforming in the optical domain through a phase-shift attenuation network composed of an adjustable phase shifter array and an adjustable optical attenuator to achieve spatial domain filtering. The weighting vector is obtained through a filtering algorithm and then split into amplitude and phase forms, that is, the signal amplitude is changed by the optical attenuator, and the phase of the microwave signal modulated on the optical carrier is changed by the adjustable phase shifter array. (5) The signal is sent to the wavelength division multiplexer WDM for multiplexing after passing through the optical delay line and the optical attenuator, and the multiplexed signal is sent to the photodetector PD for photoelectric conversion and output after passing through the optical attenuator.

[0010] The present invention proposes a novel control method for true-time-delay beamforming and spatial domain filtering. Based on performing beamforming on broadband signals using true-time-delay, combined with spatial domain filtering technology, the weights obtained from the spatial domain filtering algorithm are split into amplitude and phase forms, and the electrical domain algorithm is implemented in the optical domain by combining the adjustable optical attenuator and the adjustable phase shifter array in the optical link, thereby achieving the effect of spatial domain filtering. Compared with the existing optical domain true-time-delay beamforming technology, the present invention realizes spatial domain filtering with a large instantaneous bandwidth while implementing optical domain true-time-delay beamforming. Compared with the existing antenna nulling schemes, the present invention has advantages such as a high operating frequency band, a large instantaneous bandwidth, a high tuning accuracy, and a strong anti-electromagnetic interference ability. The system structure is simple and has strong practical operability. Description of the Drawings

[0012] Figure 1 It is the schematic diagram of a microwave photon true-time-delay beamforming and spatial domain filtering control method of the present invention; Figure 2 (a-b) are the optical domain true-time-delay beamforming patterns for 4-16 GHz signals, where the beamforming direction is 10°. It can be seen that the signal gain in the beamforming direction is the ideal gain; Figure 3 (a-b) correspond to the patterns of different frequencies with a null of 60° based on the optical domain true-time-delay beamforming. The relative bandwidth is 100 MHz, and the signal center frequency is 10 GHz. It can be seen that nulling can be achieved in a specific direction for different frequencies, and the signal-to-interference ratio after nulling is greater than 40 dB; Figure 4 (a-b) are the optical domain true-time-delay beamforming patterns for 4-16 GHz signals, where the beamforming direction is 30°. It can be seen that the signal gain in the beamforming direction is the ideal gain; Figure 5 (a-b) correspond to the patterns of different frequencies with a null of -20° based on the optical domain true-time-delay beamforming. The relative bandwidth is 100 MHz, and the signal center frequency is 10 GHz. It can be seen that nulling can be achieved in a specific direction for different frequencies, and the signal-to-interference ratio after nulling is greater than 40 dB; Figure 6(a - e) are the EVM effect diagrams and antenna pattern diagrams of a broadband desired signal with an incident direction of 10°, a center frequency of 10 GHz, and a bandwidth of 100 MHz plus a co - frequency interference with an incident direction of 60°, without true delay and anti - interference nulling, after true - delay beamforming, and after true - delay beamforming and spatial filtering. Figure 7 It is a curve graph of the null - depth varying with the signal bandwidth, where the incident direction of the desired signal is 0°, and the incident directions of the interferences are 30°, 45°, and 60° respectively. Specific implementation manner

[0013] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings: These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0014] Figure 1 It is the schematic diagram of a microwave - photon true - delay beamforming and spatial - filtering method of the present invention. In this example, it includes 8 receiving antennas, 8 directly - modulated lasers with different wavelengths, a low - noise amplifier LNA, a true - delay network composed of 8 variable optical delay lines VODL1, an adjustable phase - shifter array composed of 8 variable optical delay lines VODL2, and 8 variable optical attenuators VOA that jointly form a phase - shift and attenuation network, an 8 - channel wavelength - division multiplexer WDM, and a photodetector PD. The electrical signals received by the 8 antennas are amplified by the LNA and then loaded onto the directly - modulated lasers DML, and the 8 - channel signals are modulated onto 8 - wavelength optical carriers through direct modulation. The 8 - channel optical signals first pass through the variable optical fiber delay lines VODL1 to achieve true - delay beamforming, and then pass through the phase - shift and attenuation network composed of the variable optical delay lines VODL2 and the variable optical attenuators VOA to perform analog - domain weighting for spatial filtering. Subsequently, they are combined through the 8 - channel WDM and the optical power is adjusted using an optical attenuator, and finally input to the PD to be converted into electrical signals. At this time, the electrical signals are the signals after true - delay beamforming and spatial filtering. This scheme adopts an adaptive antenna nulling algorithm: the linear - constraint minimum - variance criterion LCMV algorithm, to obtain the weighting coefficients of the phase - shift and attenuation network, and decompose the weighting coefficients into amplitude and phase forms, that is, change the signal amplitude through the variable optical attenuator, and change the phase of the microwave signal modulated on the optical carrier through the adjustable phase - shifter array composed of variable optical delay lines, thereby realizing spatial filtering. Among them, VODL1 and VODL2 can be implemented by one VODL, making the structure simpler.

[0015] In this example, the specific implementation steps of the method are as follows: Step 1: The electrical signals received by the 8-way receiving antenna are amplified and loaded onto a directly modulated laser (DML) with optical carriers of different wavelengths for optoelectronic conversion of the signals. Set the frequency of the electrical signal received by the antenna to 10 GHz, the expected signal type to QAM signal, the interfering signal to be of the same frequency as the expected signal, the interfering signal type to LFM signal, the signal-to-interference ratio to be approximately -20 dB, the signal bandwidth to be 100 MHz. The experiment generated two groups of different signal incident directions: for the first group, the incident direction of the expected signal is 10°, and the incident direction of the interfering signal is 60°; for the second group, the incident direction of the expected signal is 30°, and the incident direction of the interfering signal is -20°. Step 2: The converted optical signals are transmitted through optical fibers to an 8-way delay-weighting array. The delay-weighting array compensates for the phase difference caused by the time difference of arrival in the required direction of the signal through adjustable optical delay lines. Since it is delay compensation, it is possible to control the beam pointing of signals within a large bandwidth range without causing "beam tilt", thereby avoiding the "aperture effect" and achieving true time-delay beamforming with a single main lobe. The simulation results are as Figure 2 (a - b) and Figure 4 (a - b) show that the true time-delay beamforming achieves single main lobe beamforming with beam pointing of 10° and 30° in the frequency range of 4 GHz to 16 GHz, and the gain is the ideal gain. Step 3: After performing true time-delay beamforming in Step 2, the signals are made to be incident along the normal direction. The signals output from the array after delay pass through a phase shift and attenuation network to achieve spatial filtering. The specific control method of the phase shift and attenuation network is as follows: the change amount of the adjustable optical attenuator is determined by the amplitude of the weighting vector obtained by the LCMV algorithm, and the change amount of the delay of the adjustable phase shifter array composed of adjustable optical delay lines is determined by the phase of the weighting vector. The conversion formula is where is the phase of the weight, f sig is the signal frequency; the weights can be obtained by using two adjacent single-tone signals with the adaptive nulling LCMV algorithm. The LCMV algorithm is a conventional beamforming algorithm, and researchers in the field of antennas are somewhat familiar with it, so it will not be elaborated in this article. The adjustment error of the adjustable optical attenuator in this scheme is 0.1 dB, and the adjustment error of the adjustable optical delay line is 1 ps. The 8-way outputs are multiplexed by an 8-way wavelength division multiplexer (WDM) and then beat by a PD into one path. This path of signal is the coherent superposition of the above 8 branch signals. The superimposed signal can achieve spatial filtering, and the interference suppression ratio reaches -42 dB, as shown in Figure 3 (a - b) and Figure 5(As shown in (a - b)), the signal recovery can also be observed through the EVM diagrams before and after signal true delay and spatial domain filtering. When there is no true delay and spatial domain filtering, the EVM of the received signal is 30.8%. After true delay beamforming, the signal EVM becomes 29.2%, with an improvement of 1.6%. After true delay beamforming and spatial domain filtering, the signal EVM is 6.1%, which is an improvement of 24.7% compared to the received signal EVM, as shown in Figure 6 (a - e). Step 4: Change the interference signal bandwidth and observe the change in the null depth when the signal bandwidth changes. The results are as shown in Figure 7 It can be seen that as the bandwidth of the interference continuously increases, the depth of the interference signal that can be suppressed gradually decreases. At the same time, it is verified that when the incident direction of the interference is 45° and 60°, the achievable null depth and the bandwidth show the same trend.

[0016] In summary, the present invention realizes a control method for microwave photon true delay beamforming and microwave photon spatial domain filtering. An optically tunable optical delay line is used to replace the traditional electrical domain phase shifter to compensate for the phase difference caused by the time difference of arrival at the shaping angle, realizing single main lobe microwave photon true delay beamforming. The nulling of broadband signals in the analog domain uses a phase shift attenuation network composed of an adjustable phase shifter array and an adjustable optical attenuator. The phase of the signal is adjusted by the adjustable phase shifter array, and then the amplitude of the signal is adjusted in combination with the optical attenuator to achieve nulling of broadband signals and achieve the effect of spatial domain filtering. The realization of the adjustable phase shifter array is not limited to being composed of N-way adjustable optical delay lines, but can also be composed of N-way phase modulators and other devices that can achieve signal phase shift; in addition, the present invention explores the relationship between the interference signal bandwidth and the interference suppression depth under the framework of this solution.

[0017] In short, the above-described implementation embodiments are only examples of the present invention and are not only used to limit the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several equivalent deformations and substitutions can be made on the basis of the content disclosed in the present invention. These equivalent deformations and substitutions, substitutions of nulling algorithms, and adjustments of frequency ranges should also be regarded as the protection scope of the present invention.

Claims

1. A microwave photon true delay beamforming and spatial domain filtering control method, the method comprising an antenna, a low noise amplifier LNA, an N-way wavelength division multiplexer WDM, an adjustable optical delay line VODL, an adjustable phase shifter array PSA (Phase-shifter-array), an adjustable optical attenuator VOA, and a photodetector PD, characterized in that: After receiving N electrical signals, N receiving antennas are amplified by low noise amplifiers LNA and then loaded onto N directly modulated lasers DML with different optical carriers to realize electro-optical conversion. The modulated optical signals are transmitted to the delay module through optical fiber. In the optical domain, a true delay network composed of an adjustable optical delay line array VODL is used to realize true delay beamforming of the modulated optical signals. The delay amount is the delay difference between each array element introduced by the signal incident angle. Subsequently, the phase shift attenuation network composed of an adjustable phase shifter array PSA and an optical attenuator VOA is used to realize weighting of the array antenna receiving signal in the analog domain. The weighted vector is obtained through a filtering algorithm and then The method is split into the form of amplitude and phase, that is, the signal amplitude is changed by an attenuator, the phase of the modulated microwave signal on the optical carrier is changed by an adjustable phase shifter array, and finally N signals are coupled into one by WDM, and photoelectric conversion and analog domain addition of N signals are realized at PD to realize spatial domain filtering. The microwave photon true delay beamforming and spatial domain filtering control method can realize true delay beamforming and spatial domain filtering at the same time by cleverly controlling the parameters of the true delay network and the phase shift attenuation network. The adjustable phase shifter array PSA can be composed of devices such as a phase modulator PM or an adjustable optical delay line VODL to achieve the effect of signal phase shifting.

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