A microwave photonic DFS and AOA measurement apparatus and method

Abstract

This invention discloses a microwave photonic DFS and AOA measurement device and method. The device obtains the DFS value through the frequency information of the intermediate frequency signal obtained by downconversion, and uses a sawtooth wave to drive the DC port of the modulator, thereby introducing a frequency shift into the transmitted signal to determine the DFS direction. Simultaneously, the DC signal after photodetection contains the phase difference information of the two echo signals, which can be used to construct an amplitude comparison function to measure the AOA. This invention has the following main advantages: 1. This invention does not require an additional reference signal or back-end waveform analysis to determine the DFS direction; 2. This invention is applicable to long-distance links and is unaffected by periodic power fading caused by optical fibers; 3. This invention does not require polarization devices, has a simple structure, and is a stable system.

Description

Technical Field

[0001] This invention belongs to the field of microwave and optical communication technology, specifically relating to a microwave photonic DFS and AOA measurement device and method. Background Technology

[0002] Microwave measurement plays an indispensable role in radar, military operations, and communication systems. Among the various parameters of microwave signals, the angle of arrival and Doppler shift are two crucial parameters. These two parameters can be used to determine the position, orientation, and radial velocity of a moving target. Currently, traditional electrical-based measurement methods face technical bottlenecks such as limited bandwidth, poor stability, and electromagnetic interference. Microwave photonic measurement methods, combining the advantages of electronics and photonics, have attracted widespread attention due to their wide bandwidth, high measurement speed, and resistance to electromagnetic interference. Existing microwave photonic Doppler frequency shift (DFS) and angle of arrival (AOA) measurement schemes typically require the addition of reference signals or rely on complex back-end waveform analysis, which not only affects the system's flexibility and adjustability but also increases its complexity. Furthermore, in electronic warfare, microwave signal receivers face the risk of detection by the enemy. Currently, the radio access unit (RAU) of most measurement systems is located close to the central office (CO), meaning the entire measurement system could be destroyed in the event of enemy interference or attack. Long-distance fiber optic transmission can effectively isolate the microwave signal receiving system from the central station. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a microwave photonic DFS and AOA measurement device and method. This device obtains the DFS value through the frequency information of the intermediate frequency signal obtained by down-conversion, and uses a sawtooth wave to drive the DC port of the modulator, thereby introducing a frequency shift into the transmitted signal to determine the DFS direction. Simultaneously, the DC signal after photodetection contains the phase difference information of the two echo signals, which can be used to construct an amplitude comparison function to measure the AOA. This invention has the following main advantages: 1. This invention does not require an additional reference signal or back-end waveform analysis to determine the DFS direction; 2. This invention is applicable to long-distance links and is unaffected by periodic power fading caused by optical fibers; 3. This invention has no polarization devices, has a simple structure, and is a stable system.

[0004] The technical solution adopted by this invention to solve its technical problem is as follows: A microwave photonic DFS and AOA measurement device includes a laser diode (LD), a dual-drive dual parallel MAG modulator (D-DPMZM), an electrical power divider, an electrical phase shifter, an optical filter (OBPF), a single-mode fiber (SMF), and a photodetector (PD). The dual-drive dual-parallel MAZM modulator (D-DPMZM) includes a Y-type optical beamsplitter, a Y-type optical coupler, two sub-modulators connected in parallel, and a main bias; the two sub-modulators are DDMZM1 and DDMZM2, which are dual-drive MAZM modulators; the two arms of the Y-type optical beamsplitter are respectively connected to the two sub-modulators, and the output optical signals of the two sub-modulators are coupled through the Y-type optical coupler; DDMZM1 and DDMZM2 are both dual-electrode modulators, and each of DDMZM1 and DDMZM2 contains two radio frequency electrodes; The output port of the laser diode LD is connected to the optical signal input terminal of the D-DPMZM, the optical signal output terminal of the D-DPMZM is connected to the common input terminal of the optical filter OBPF, the output terminal of the optical filter OBPF is connected to the input terminal of the single-mode fiber SMF, the output terminal of the single-mode fiber SMF is connected to the photodetector PD, and the output terminal of the photodetector PD outputs a DC signal and an intermediate frequency signal.

[0005] A microwave photon DFS and AOA measurement method includes the following steps: Step 1: The optical carrier output from the laser diode is divided into two equal paths in the D-DPMZM. One path is modulated by two echo signals in DDMZM1, while the other optical carrier is modulated by the transmission signal in DDMZM2. Step 2: The transmitted signal is split into two paths. One path is emitted and reflected by the target to form an echo signal. This echo signal is then split into two paths by a power divider. One path of the echo signal is input to one RF port of the dual-drive MAZM1 modulator, and the other path is connected to an electrical phase shifter and input to the other RF port of the dual-drive MAZM1 modulator. The other transmitted signal is used as a transmission signal and input to one RF port of the dual-drive MAZM2 modulator. The other RF port is left unloaded. The DC port of the dual-drive MAZM2 modulator is driven by a sawtooth wave. The D-DPMZM master modulator is biased at its maximum point to couple the two optical signals. Step 3: The coupled optical signal is transmitted to the optical filter OBPF to filter out the upper sideband. The filtered optical signal is then transmitted through the single-mode fiber SMF and enters the photodetector PD for photoelectric detection to obtain the DC signal and intermediate frequency signal. The DC signal contains the echo signal phase difference information, i.e., AOA information; the intermediate frequency signal contains DFS information. The DFS and AOA to be measured can be obtained through back-end processing.

[0006] The beneficial effects of this invention are as follows: This invention's device obtains the DFS value from the intermediate frequency signal obtained through down-conversion, and uses a sawtooth wave to drive the DC port, thereby introducing a frequency shift into the transmitted signal to determine the DFS direction. Simultaneously, the DC signal after photodetection contains the phase difference information of the two echo signals, which can be used to construct an amplitude comparison function to measure the AOA. This invention has a simple structure, can suppress periodic power fading, has no polarization devices, and is system-stable. This solution has great application potential in electronic warfare and military operations. Attached Figure Description

[0007] Figure 1 This is a diagram of the microwave photonic DFS and AOA measurement device of the present invention; Figure 2 The diagram shows the DFS measurement error before and after adding optical fiber in an embodiment of the present invention. (a) is the DFS measurement result without optical fiber, and (b) is the DFS measurement result after adding 29.706km of optical fiber.

[0008] Figure 3 This is a DFS direction discrimination spectrum diagram of an embodiment of the present invention; Figure 4 This is a diagram showing the AOA measurement results of an embodiment of the present invention. Detailed Implementation

[0009] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0010] like Figure 1 As shown, the technical solution adopted in this invention is as follows: the device includes a laser diode (LD), a dual-drive dual-parallel Mach-Zehnder modulator (D-DPMZM), an electrical power divider, an electrical phase shifter, an optical band pass filter (OBPF), a single-mode fiber (SMF), and a photodetector (PD).

[0011] The LD's output port connects to the optical signal input port of the D-DPMZM, the D-DPMZM's optical signal output port connects to the common input port of the OBPF, the OBPF's output port connects to the SMF input port, the SMF's output port connects to the PD, and the PD output port outputs a DC signal and an intermediate frequency signal. The D-DPMZM consists of a Y-type optical beam splitter, a Y-type optical coupler, and two sub-modulators (DDMZM1 and DDMZM2) connected in parallel. Both DDMZM1 and DDMZM2 are dual-drive modulators, each containing two RF input ports.

[0012] The present invention includes the following steps in operation: (1) The continuous optical carrier output from the LD is injected into the D-DPMZM. The optical carrier output from the laser generates two identical optical paths in the D-DPMZM. One path is modulated by two echo signals in DDMZM1, while the other optical carrier is modulated by the transmission signal in DDMZM2. (2) After the echo signal is divided equally by the power divider, one path is input to one radio frequency (RF) port of DDMZM1, and the other path is connected to the phase shifter and then input to the other RF port of DDMZM1. The transmission signal is input to one RF port of DDMZM2, and no RF signal is input to the other RF port. The DC port of DDMZM2 is driven by a sawtooth wave. The D-DPMZM master modulator is biased at the maximum point; (3) The D-DPMZM output optical signal is transmitted to the OBPF to filter out the upper sideband. The filtered optical signal is transmitted through the SMF and then enters the PD photoelectric detection to obtain the DC signal and the intermediate frequency signal. The principle of this invention: The output optical signal of the LD is represented as , and The frequency and amplitude of the optical carrier are respectively represented by the input DDMZM1 echo signal as follows: and , It is the amplitude of the echo signal. It is the echo signal frequency. This is the phase difference between the two echo signals. When the DDMZM1 operates at its minimum point, the output optical field can be expressed as: (1) in For the loss of DDMZM1, It is the modulation index. It is a half-wave voltage. It is a first-order Bessel function. Higher-order Bessel functions are ignored in the derivation, considering the finite modulation index.

[0013] The optical carrier is modulated by the transmission signal in the DDMZM2. The transmission signal is injected into one RF port of the DDMZM2, while the other RF port is unloaded. Simultaneously, a sawtooth wave signal is added to the DC port of the DDMZM2 to introduce a frequency shift for determining the DFS direction. The transmission signal is represented as follows: ,in It is the amplitude of the transmitted signal. It is the transmission signal frequency; the sawtooth wave frequency is... If the amplitude of the sawtooth wave is twice the half-wave voltage of the modulator, then the optical field output by the DDMZM2 can be expressed as: (2) in For the loss of DDMZM1, This is the modulation index of DDMZM2. The main modulator of D-DPMZM is biased at its maximum point, and the output coupled optical signal is transmitted to the OBPF. The OBPF is used to filter out the optical carrier and lower sideband, thus avoiding power fading caused by double-sideband destructive interference. The signal output by the OBPF can be written as: (3) in This represents the loss of the OBPF. After the optical signal is transmitted through the SMF, the output optical field is as follows: (4) in These are the phase shifts introduced by dispersion on the echo signal and the transmitted signal, respectively.

[0014] Then, the current obtained after the optical signal is photodetected in the PD can be expressed as: (5) in For PD response, , As can be seen from equation (5), the DFS value and direction can be obtained from the intermediate frequency signal. The phase difference of the echo signal... Then it can be obtained from DC signal The angle of arrival is obtained and then calculated according to formula (6). .

[0015] (6) Example: In this embodiment, the device includes: LD, D-DPMZM, OBPF, SMF, PD, RF signal source, power divider, phase shifter, and spectrum analyzer. The D-DPMZM consists of a Y-type optical beam splitter, a Y-type optical coupler, and two sub-modulators (DDMZM1 and DDMZM2) connected in parallel. Both DDMZM1 and DDMZM2 are dual-drive modulators and each includes two RF input ports.

[0016] The LD's output port connects to the optical signal input port of the D-DPMZM. The D-DPMZM's optical signal output port connects to the common input port of the OBPF. The OBPF's output port connects to the SMF input port. The SMF's output port connects to the PD. The PD output port outputs both DC and IF signals. The echo signal is split equally by the power divider, with one path input to one RF port of DDMZM1 and the other path connected to an electrical phase shifter before inputting to the other RF port of DDMZM1. The transmission signal is input to one RF port of DDMZM2, while the other RF port remains unloaded. The DC port of DDMZM2 is driven by a sawtooth wave.

[0017] In this embodiment, the specific implementation steps of the method are as follows: Step 1: The continuous optical carrier output wavelength generated by the LD is 1550nm and the power is 23mw; the transmission signal frequency generated by the RF signal source is 12GHz and the power is 15dBm; the D-DPMZM half-wave voltage is 3.5V and the operating bandwidth is above 30GHz; the bandwidth of the PD is 40GHz.

[0018] Step 2: Without SMF, set the phase shifter to 0 degrees. Adjust the DFS value from -100kHz to 100kHz in 10kHz steps, meaning the echo signal frequency is adjusted from 11.9999GHz to 12.0001GHz in 10kHz steps. Record the output intermediate frequency signal using an oscilloscope, collecting five sets of data at each frequency point to calculate the average error. The results are as follows: Figure 2 As shown in section (a), the solid black circles in the vertical bars represent the average measurement error of different DFS, and the black bars represent the measurement error range of different DFS. It can be seen that the measurement error range of this invention without optical fiber is ±0.2Hz. Then, a 29.706km SMF was added to the system, and the above steps were repeated. The measured DFS results are as follows... Figure 2 As shown in part (b), its error range is within ±0.25Hz, which shows that the present invention still has good DFS measurement capability in long-distance application scenarios.

[0019] Step 3: Set the transmitted signal and echo signal to 12 GHz and 12.0006 GHz respectively, i.e., DFS is +0.6 MHz. The resulting electrical spectrum is as follows. Figure 3 The dotted line in the image shows the signal. The echo signal was then adjusted to 11.9994 GHz, i.e., DFS was -0.6 MHz. The spectrum is shown in the image. Figure 3 As shown by the solid line in the diagram, it can be seen that by using a 1MHz sawtooth wave signal to drive the DC port of the DDMZM2, the frequency shift of the transmitted signal was successfully achieved, thereby realizing DFS direction discrimination.

[0020] Step 4: Fix the frequencies of the transmitted signal and the echo signal to 12GHz and 12.1GHz respectively, with a power of 15dBm for both. An electric phase shifter is used to simulate the phase difference between the echo signals received by the two antennas by varying the phase difference from 0 to 180 degrees in 10-degree increments. A digital multimeter is used after the PD to measure the DC voltage under different phase differences, constructing an amplitude comparison function to achieve AOA measurement. As can be seen from equation (6), when the phase difference varies within the range of 0-180°, ambiguity-free AOA measurement can be achieved within the range of 0-90°. The results are as follows: Figure 4As shown in the figure, the solid dots represent the measured phase difference, the black lines represent the actual phase difference, and the stars represent the measurement error of the phase difference. The AOA measurement error of this invention is ±1.5 degrees.

[0021] In summary, the microwave photonic DFS and AOA measurement device and method of the present invention are simple and easy to implement, and can achieve high-precision DFS and AOA measurements over a wide bandwidth. At the same time, the DFS direction can be clearly identified without additional reference signals and complex back-end analysis. The present invention is highly promising for applications such as electronic warfare.

Claims

1. A microwave photonic DFS and AOA measurement apparatus, characterized in that, This includes laser diodes (LDs), dual-drive dual parallel MAG modulators (D-DPMZMs), power dividers, phase shifters, optical filters (OBPFs), single-mode fiber optics (SMFs), and photodetectors (PDs). The dual-drive dual-parallel MAZM modulator (D-DPMZM) includes a Y-type optical beamsplitter, a Y-type optical coupler, two sub-modulators connected in parallel, and a main bias; the two sub-modulators are DDMZM1 and DDMZM2, which are dual-drive MAZM modulators; the two arms of the Y-type optical beamsplitter are respectively connected to the two sub-modulators, and the output optical signals of the two sub-modulators are coupled through the Y-type optical coupler; DDMZM1 and DDMZM2 are both dual-electrode modulators, and each of DDMZM1 and DDMZM2 contains two radio frequency electrodes; The output port of the laser diode LD is connected to the optical signal input terminal of the D-DPMZM, the optical signal output terminal of the D-DPMZM is connected to the common input terminal of the optical filter OBPF, the output terminal of the optical filter OBPF is connected to the input terminal of the single-mode fiber SMF, the output terminal of the single-mode fiber SMF is connected to the photodetector PD, and the output terminal of the photodetector PD outputs a DC signal and an intermediate frequency signal. Among them, DDMZM1 operates at the minimum point, a sawtooth wave signal is added to the DC port of DDMZM2, and a frequency shift is introduced to identify the DFS direction. The main modulator of D-DPMZM is biased at the maximum point, and the output coupled optical signal is transmitted to OBPF. OBPF is used to filter out the optical carrier and lower sideband.

2. A measuring method using the apparatus as claimed in claim 1, characterized in that, Includes the following steps: Step 1: The optical carrier output from the laser diode is divided into two equal paths in the D-DPMZM. One path is modulated by two echo signals in DDMZM1, while the other optical carrier is modulated by the transmission signal in DDMZM2. Step 2: The transmitted signal is split into two paths. One path is emitted and reflected by the target to form an echo signal. This echo signal is then split into two paths by a power divider. One path of the echo signal is input to one RF port of the dual-drive MAZM1 modulator, and the other path is connected to an electrical phase shifter and input to the other RF port of the dual-drive MAZM1 modulator. The other transmitted signal is used as a transmission signal and input to one RF port of the dual-drive MAZM2 modulator. The other RF port is left unloaded. The DC port of the dual-drive MAZM2 modulator is driven by a sawtooth wave. The D-DPMZM master modulator is biased at its maximum point to couple the two optical signals. Step 3: The coupled optical signal is transmitted to the optical filter OBPF to filter out the upper sideband. The filtered optical signal is then transmitted through the single-mode fiber SMF and enters the photodetector PD for photoelectric detection to obtain the DC signal and the intermediate frequency signal. The DC signal contains the echo signal phase difference information, i.e., AOA information. The intermediate frequency signal contains DFS information, and the DFS and AOA to be tested can be obtained through back-end processing.

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