Dual-band phased array radar coherent receiving method based on light pulses

Abstract

A coherent reception method for dual-band phased array radar based on optical pulses includes an optical pulse generator, an amplifier, an adjustable delay line, a modulator, a photodetector, a low-pass filter, an electrical phase shifter, a multi-channel coupler, and an electrical analog-to-digital converter. Its key feature is that by utilizing optical pulses, only one set of equipment is needed to achieve frequency conversion, phase shifting, and digitization of dual-band phased array radar signals. The same devices are used for frequency conversion, phase shifting, and digitization of signals in different frequency bands of the dual-band phased array radar signal, eliminating the severe degradation of inter-band coherence caused by device differences when using devices for different frequency bands in the past. This ensures coherent reception of dual-band phased array radar signals and significantly reduces the cost and size of the dual-band phased array radar.

Description

Technical Field

[0001] This invention relates to microwave photonics technology, specifically a coherent reception method for a dual-band phased array radar based on optical pulses. Background Technology

[0002] Phased array radars control beam direction electronically, offering numerous advantages such as high directivity, anti-jamming capabilities, improved signal-to-noise ratio, and fast scanning response. Since their introduction in the 1950s, they have been widely used in radar and communication systems in military, aerospace, and radio astronomy fields. In radar and communication systems, simultaneous multi-mode and multi-band operation of transceivers is a growing trend. Furthermore, many applications require transceivers to operate over a wide range of radio frequency frequencies. These trends also apply to phased array systems. Multi-band reception in phased array systems faces many challenges. Due to bandwidth limitations of electronic equipment, the reception and digitization of multi-band signals require multiple frequency conversions to intermediate frequencies. On the other hand, different phase shifters are needed to achieve beamforming for different band signals. Frequency conversion, phase shifting, and digitization of multi-band signals require multiple sets of equipment for different bands. These devices not only limit the operating bandwidth but also impose a significant burden on the size and cost of the phased array radar receiving system. Moreover, the differences between these devices lead to poor consistency across bands, severely affecting the coherence of multi-band signal reception.

[0003] Over the past few decades, various solutions have been explored to achieve dual-band reception in phased array radar. Separating cross-band signals using filters is the most readily conceived method. The separated signals are then phase-controlled via microwave phase shifters to meet the different phase-shifting requirements of different bands [S. Jeon et al., "AScalable 6-to-18GHz Concurrent Dual-Band Quad-Beam Phased-Array Receiver in CMOS," in IEEE Journal of Solid-State Circuits, vol.43, no.12, pp.2660-2673.]. This method integrates two sets of TR components using CMOS technology, reducing system size and cost, but still requires two complete systems and cannot guarantee coherent reception between the two bands. Optical beamforming networks employing true optical delay technology can achieve phase compensation over a wide bandwidth by compensating for the delay difference between antenna elements [C. Tsokos, et al., "Optical Beamforming Network for Multi-Beam Operation With Continuous Angle Selection," in IEEE Photonics Technology Letters, vol. 31, no. 2, pp. 177-180.]. However, optical beamforming networks lack the means to receive and digitize multi-band signals via frequency conversion.

[0004] An optical pulse consists of a series of longitudinal modes in the optical spectrum. These modes have fixed frequency intervals and are mutually phase-locked, and can be regarded as a comb-shaped set of coherent local oscillators. Therefore, multi-band coherent reception can be easily achieved using optical pulses. This invention proposes a coherent reception method for dual-band phased array radar based on optical pulses. This technology utilizes optical pulses, optical delay lines, and electrical phase shifters to realize the frequency conversion, phase shifting, and digitization of dual-band phased array radar signals based on a single set of equipment, while ensuring high coherence between the two band signals. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a coherent reception method for a dual-band phased array radar based on optical pulses. The method includes an optical pulse generator, a modulator, an adjustable delay line, a photodetector, an analog-to-digital converter, an electrical phase shifter, and an amplifier. The optical pulse generator is used to generate a repetition frequency of f. s The period is T sThe optical pulse is generated by amplifying the signal output from the antenna array element and then modulating it onto the optical pulse by a modulator. An adjustable delay line is used to adjust the delay between the optical pulse generator and the modulator. A photodetector is used to achieve photoelectric conversion, and its bandwidth is [missing information]. PIN diodes or APD diodes can be used. The bandwidth of the low-pass filter is... Electrical phase shifters are used to achieve phase adjustment of microwave signals, and their bandwidth should be greater than [missing information]. A multiplexer combines multiple outputs into a single input, which is then fed into an analog-to-digital converter (ADC). The ADC is used to quantize and encode electrical signals at a sampling rate of f. s It maintains the same repetition frequency as the light pulse generator.

[0006] The technical solution of the present invention is as follows:

[0007] A coherent reception method for a dual-band phased array radar based on optical pulses, characterized in that the method includes:

[0008] N optical pulses with fixed repetition rates are generated using N optical pulse generators and transmitted to the modulator via an adjustable extension line;

[0009] The dual-band signal output from the antenna array element is amplified by an amplifier and then modulated onto each optical pulse by the modulator. The two frequency signals in the dual-band signal are respectively mixed with different frequency longitudinal modes of the optical pulse to generate a frequency-converted signal. Two copies of the signal within the range;

[0010] The two signal copies are converted into electrical signals by a photodetector and then filtered by a low-pass filter, retaining only the original signals. The signal replicas within the range complete the downconversion of the dual-band signal;

[0011] Each filtered electrical signal is input to an electrical phase shifter for phase adjustment, then combined into a single signal by a multiplexer, and finally quantized and encoded by an electrical analog-to-digital converter to obtain a digital signal.

[0012] The sampling rate of the electrical analog-to-digital converter is consistent with the repetition rate of the optical pulse generator.

[0013] Furthermore, when beamforming is achieved by phase shifting the dual-band signal, the phase shift required for the corresponding channel of the dual-band signal is calculated based on the spatial coordinates of each antenna element. and Based on the phase shift of the aforementioned dual-band signal and Calculate the required delay Δt of the adjustable delay line and the phase shift of the electrical phase shifter for each channel. By adjusting the adjustable delay line Δt, the two frequency signals in the dual-band signal are made to have different phase shifts; by adjusting the electrical phase shifter, the two frequency signals in the dual-band signal are shifted to a specified phase value respectively.

[0014] Beamforming is achieved by downconverting dual-band signals using optical pulses and independently adjusting the phases of different frequency signals in the dual-band signals using adjustable delay lines and electrical phase shifters.

[0015] The adjustable delay line only needs to satisfy the delay range of [0, T] s This allows for continuous 360-degree phase adjustment of the signal, where T... s The pulse light repetition period is defined as the signal's phase. Therefore, arbitrary phase adjustment of the dual-band signal can be achieved simply by adjusting the adjustable delay line and the electrical phase shifter. Through independent phase control of the band signals, beamforming of the dual-band signals can be realized, thereby enabling the reception and digitization of the dual-band signals.

[0016] The signal after photoelectric conversion needs to be processed Low-pass filtering can achieve a bandwidth of It can be achieved using a photodetector, or by adding an additional filter later.

[0017] The aforementioned optical pulse generator is used to generate a repetition frequency of f. s The optical pulses can be generated using, but are not limited to, active mode-locked lasers, passive mode-locked lasers, or optical frequency combs generated based on external modulation methods.

[0018] The modulator is used to modulate microwave signals onto optical pulses, and may be, but is not limited to, lithium niobate electro-optic modulators, polymer electro-optic modulators, silicon-based integrated electro-optic modulators, acousto-optic modulators, or spatial light modulators.

[0019] The adjustable delay line is used to adjust the delay between the optical pulse generator and the modulator, and can be, but is not limited to, an electric delay line, a micro-ring delay line, or a delay line based on a high-order dispersion fiber.

[0020] The aforementioned analog-to-digital converter can be, but is not limited to, an oscilloscope, an analog-to-digital converter chip, or a signal development board.

[0021] The photodetector may be, but is not limited to, a PIN diode or an APD diode.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) For any dual-band signal, adaptive downconversion to a higher frequency is achieved by mixing with the optical pulse. Within this range, multi-stage local oscillators are not required for signals in different frequency bands.

[0024] (2) For any dual-band signal, as long as the frequencies f1 and f2 of the dual-band signal are not in the same frequency region, that is, they are not mixed with the same optical pulse frequency in longitudinal mode, the 360-degree independent phase adjustment of the dual-band signal can be achieved.

[0025] (3) Reduced the delay pressure of the adjustable delay line, so that the delay line only needs to be in [0,T] s Adjustment can achieve 360-degree phase shift of microwave signals.

[0026] (4) A single set of equipment can be used to achieve frequency conversion, phase shifting and digitization of any dual-band signal, which greatly reduces the cost and size of the system, while ensuring the coherence between the two band signals during the reception process. Attached Figure Description

[0027] Figure 1 This is an overall architecture diagram of an embodiment of the coherent reception method for dual-band phased array radar based on optical pulses according to the present invention;

[0028] Figure 2 This is a schematic diagram illustrating the application of optical pulses to down-convert dual-band signals.

[0029] Figure 3 This is a schematic diagram of the interval phase characteristics of the phase change caused by optical pulse delay adjustment.

[0030] Figure 4 Dual-band signal phase shifting principle

[0031] Figure 5 is a schematic diagram of a frequency conversion and phase shift embodiment of a dual-band signal. Detailed Implementation

[0032] A specific embodiment of the present invention is given below with reference to the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and processes, but the scope of protection of the present invention is not limited to the following embodiment.

[0033] Please see Figure 1 , Figure 1This is an overall architecture diagram of an embodiment of the coherent reception method for dual-band phased array radar based on optical pulses according to the present invention. As shown in the diagram, it includes an optical pulse generator, a modulator, an adjustable delay line, a photodetector, a low-pass filter, an electrical phase shifter, a multiplexer, an analog-to-digital converter, and an amplifier. The optical pulse generator is an active mode-locked laser, and its output is connected to the input of the adjustable delay line. In this embodiment, the adjustable delay line is an electrically adjustable delay line, and its output is connected to the optical input of the modulator. The amplifier is a power amplifier, and its output is connected to the modulator. The modulator is a Mach-Zehnder intensity modulator, and its output is connected to the input of the photodetector. The output of the photodetector is connected to the low-pass filter. The low-pass filter is connected to the input of the electrical phase shifter. The output of the electrical phase shifter is connected to the multiplexer. The multiplexer couples multiple signals into one, which is then connected to the input of the analog-to-digital converter.

[0034] The aforementioned optical pulse generator is used to generate a repetition frequency of f. s The period is T s The optical pulse is generated by amplifying the signal output from the antenna array element and then modulating it onto the optical pulse by a modulator. An adjustable delay line is used to adjust the delay between the optical pulse generator and the modulator. A photodetector is used to achieve photoelectric conversion, and its bandwidth is [missing information]. PIN diodes or APD diodes can be used. The bandwidth of the low-pass filter is... Electrical phase shifters are used to achieve phase adjustment of microwave signals, and their bandwidth should be greater than [missing information]. A multiplexer combines multiple outputs into a single input, which is then fed into an analog-to-digital converter (ADC). The ADC is used to quantize and encode electrical signals at a sampling rate of f. s The repetition frequency is consistent with that of the optical pulse generator. The working principle of this invention is described below.

[0035] The optical pulse generator produces optical pulses, and its time-domain and frequency-domain expressions can be written as follows:

[0036]

[0037]

[0038] Where A = 2f s Optical pulses appear as pulse sequences in the time domain and as pulses with intervals of f in the frequency domain. s The set of frequency components (frequency comb). The dual-band frequency signal s(t) = cos(2πf1t) + cos(2πf2t) is modulated onto the optical pulse by a sampling gate modulator. In the frequency domain, it is manifested as mixing between the longitudinal modes of different frequencies of the signal and the optical pulse. The dual-band signal will establish signal copies on both sides of each frequency component of the optical pulse. The process of the signal being modulated onto the optical pulse can be represented as:

[0039]

[0040] Where T M Let be the transfer function of the modulator, and α be related to the modulation depth. After photoelectric conversion by the photodetector, the bandwidth is... The low-pass filter filters the output signal. Ignoring the DC component, the output of the low-pass filter is only... The signal copy of the dual-band signal within the range. At this point, the down-conversion process of the dual-band signal is complete, such as... Figure 2 As shown. It can be expressed by the formula:

[0041]

[0042] Where n1, n2 = 0, 1, 2... are the values ​​of f1 and f2 of the two-band signal s(t) mixed to... The corresponding optical pulse frequency longitudinal mode, B is the amplitude of the signal at this time.

[0043] When the delay line is changed to delay the light pulse by Δt, the output after the delay, according to the above formula, is:

[0044] I′(t)={T M [s(t)]×u(t+Δt)}*h oe (t)

[0045] =B[cos(2π(f1±n1f)] s (t+Δt))+cos(2π(f2±n2f) s (t+Δt))]

[0046] =B[cos(2π(f1±n1f)] s )t±2πn1f s Δt)+cos(2π(f2±n2f s )t±2πn2f s Δt)]

[0047] At this time, the phases of the signals with frequencies f1 and f2 have shifted by ±2πn1f, respectively. s Δt and ±2πn2f s Δt, the phase shift generated by adjusting the delay line has a range characteristic, that is, the phase shift is different in different frequency ranges, such as... Figure 3 As shown. The electrical phase shifter is modified to perform additional phase shifting. At this time, the output of the phase shifter is:

[0048]

[0049] The phase shift of the signal with frequency f1 in the altered signal I(t) is: The phase shift of the signal with frequency f2 is Therefore, when n1≠n2, that is, when frequencies f1 and f2 are not in the same frequency range and are not mixed with the longitudinal modes of the same optical pulse, the delay amount Δt of the delay line and the phase shift amount of the electric phase shifter can be controlled. To perform phase shifting on signals of different frequencies in a dual-band signal, such as... Figure 4 As shown. When it is necessary to phase shift two different frequency signals f1 and f2 in a dual-band signal respectively. and At that time, Δt and need to be adjusted as follows:

[0050]

[0051] further The delay line only needs to be in [0,T] s 360-degree phase adjustment of dual-band signals can be achieved by adjusting within a certain range. Therefore, arbitrary phase adjustment of dual-band signals can be achieved simply by adjusting the adjustable delay line and the electrical phase shifter as described above. By independently controlling the phase of the band signals, beamforming of dual-band signals can be realized, thereby enabling the reception and digitization of dual-band signals.

[0052] The above-mentioned coherent reception method for dual-band phased array radar based on optical pulses includes the following steps:

[0053] 1) The optical pulse generator described above produces a repetition rate of f. s The optical pulses are modulated by a modulator onto the dual-band signals.

[0054] 2) In the dual-band signal, frequencies f1 and f2 are mixed with different longitudinal modes of the optical pulse to generate a frequency-converted signal. Signal copies within range, such as Figure 2 As shown.

[0055] 3) After photoelectric conversion, the microwave signal is filtered by a low-pass filter, retaining only the signal from the photoelectric signal. The signal copy within the range is used to complete the downconversion of the dual-band signal, as shown in Figure 5(a).

[0056] 4) The low-pass filtered signal is output to the phase shifter. The signal output by the phase shifter is combined into one by the multiplexer and then quantized and encoded by the analog-to-digital converter to obtain a digital signal.

[0057] 5) When it is necessary to phase-shift dual-band signals to achieve beamforming, the specific values ​​of phase shifting required for the dual-band signals in the corresponding channel are calculated based on the spatial arrangement information of each antenna element. and

[0058] 6) Based on and The calculation yields the required delay value Δt of the adjustable delay line and the phase shift value of the electric phase shifter for each channel.

[0059] 7) Adjust the adjustable delay line Δt to produce different phase shifts in frequencies f1 and f2, as shown in Figure 5(b). Adjust the electrical phase shifter to shift the dual-band signal frequencies f1 and f2 to the specified values, as shown in Figure 5(c).

[0060] In the above process, down-conversion of the dual-band signal is achieved through optical pulses, and independent phase adjustment of different frequency signals in the dual-band signal is completed by adjusting the adjustable delay line and the electrical phase shifter. Experiments show that the present invention can use the above-described equipment to realize frequency conversion, phase shifting, and digitization of dual-band signals, and complete coherent reception of dual-band signals. The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made on the basis of the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coherent reception method for a dual-band phased array radar based on optical pulses, characterized in that, The method includes: N optical pulses with fixed repetition rates are generated using N optical pulse generators and transmitted to the modulator via an adjustable delay line; The dual-band signal output from the antenna array element is amplified by an amplifier and then modulated onto each optical pulse by the modulator. The two frequency signals in the dual-band signal are mixed with different frequency longitudinal modes of the optical pulse to generate a frequency-converted DC-DC converter. Two copies of the signal within the range; The two signal copies are converted into electrical signals by a photodetector and then filtered by a low-pass filter, retaining only DC-1 signals. The signal replicas within the range complete the downconversion of the dual-band signal; Each filtered electrical signal is input to an electrical phase shifter for phase adjustment, then combined into a single signal by a multiplexer, and finally quantized and encoded by an electrical analog-to-digital converter to obtain a digital signal. The sampling rate of the analog-to-digital converter is consistent with the repetition rate of the optical pulse generator; When beamforming is achieved by phase shifting a dual-band signal, the phase shift required for the corresponding channel is calculated based on the spatial coordinates of each antenna element. and Based on the phase shift of the dual-band signal and Calculate the delay required for each channel using an adjustable delay line. Phase shifting of electric phase shifters By adjusting the adjustable delay line This causes the two frequency signals in the dual-band signal to have different phase shifts; by adjusting the electric phase shifter, the two frequency signals in the dual-band signal are shifted to a specified value respectively; When it is necessary to separately analyze two different frequency signals in a dual-band signal Phase shifting separately and When, adjust the delay amount of the adjustable delay line. Phase shift of the electric phase shifter for: ； The signal after photoelectric conversion needs to be DC- The low-pass filter, with a bandwidth of DC- This can be achieved through a photodetector, or by adding an additional filter later. The optical pulse generator is an active mode-locked laser, a passive mode-locked laser, or an optical frequency comb generated based on an external modulation method.

2. The coherent reception method for dual-band phased array radar based on optical pulses according to claim 1, characterized in that, The delay range of the adjustable delay line satisfies This allows for continuous 360-degree phase adjustment of the signal, where... This is the light pulse repetition period.

3. The coherent reception method for a dual-band phased array radar based on optical pulses according to claim 1, characterized in that, The modulator is a lithium niobate electro-optic modulator, a polymer electro-optic modulator, a silicon-based integrated electro-optic modulator, an acousto-optic modulator, or a spatial light modulator.

4. The coherent reception method for dual-band phased array radar based on optical pulses according to claim 1, characterized in that, The adjustable delay line is used to adjust the delay between the optical pulse generator and the modulator, and can be an electric delay line, a micro-ring delay line, or a delay line based on high-order dispersion fiber.

5. The coherent reception method for dual-band phased array radar based on optical pulses according to claim 1, characterized in that, The aforementioned analog-to-digital converter can be an oscilloscope, an analog-to-digital converter chip, or a signal development board.

6. The coherent reception method for a dual-band phased array radar based on optical pulses according to claim 1, characterized in that, The photodetector is a PIN diode or an APD diode.

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