A microwave photonic phased array receiving beamforming network

Abstract

The present invention discloses a microwave photon phased array receiving beam forming network, comprising: a plurality of optical channels, each optical channel comprising a laser, a front-end electro-optical intensity modulator, an erbium-doped fiber amplifier and an optical true delay unit connected in sequence; the output end of the optical true delay unit is connected to the input end of a wavelength division multiplexer; the output end of the wavelength division multiplexer is connected to the input end of a 1×2 optical power splitter, the output end of the 1×2 optical power splitter is connected to two optical links, each optical link comprises a rear-end electro-optical intensity modulator and a photodetector connected in sequence, and the output ends of the two photodetectors are connected to the input end of an electrical signal differentiator 9. The microwave photon phased array receiving beam forming network disclosed by the present invention can down-convert all received signals using a single local oscillator at the rear end of the forming network, without the need to perform coherent distribution of clock and local oscillator signals at the front end of the array, thereby reducing the weight and structural complexity of the array.

Description

Technical Field

[0001] The invention belongs to the field of phased array antennas, and in particular relates to a microwave photon phased array receiving beam forming network. Background Art

[0002] The technological development in the future military operations and civil communications has put forward technical requirements for phased array systems, such as large bandwidth, high frequency, and reconfigurability. The phased array system implemented with the current digital architecture cannot meet the future ultra-wideband and array requirements. This is reflected in the following aspects: Under this architecture, its clock and local oscillator signals are distributed to each set of T / R components at the array end, which puts forward extremely high requirements for the synchronization and coherent transmission of time-frequency signals; in addition, since the bandwidth of the ADC is much smaller than the RF bandwidth of the multi-function coverage, the broadband RF signal will undergo analog signal processing such as frequency conversion, filtering, and channelization before digitization; and currently, a single electronic device is difficult to support ultra-wideband analog processing, and it is also impossible to achieve ultra-wideband tunable processing, so different hardware support is still required for each band; on the other hand, the traditional RF transmission method cannot maintain a uniform and high dynamic range within the ultra-wideband, so the RF signal must be converted to a low frequency or digital signal very close to the antenna. These hardware for each antenna cannot be concentrated together, which will inevitably cause further hardware redundancy in the case of multiple antennas or arrays. This greatly increases the weight, volume and structural complexity of the antenna array, and significantly reduces the battlefield survivability and platform adaptability of the phased array array.

[0003] Microwave photonic technology has the characteristics of large bandwidth, low transmission loss, anti-electromagnetic interference, light weight and small size, and is expected to break through the shortcomings of traditional digital phased arrays. Based on the achievements of microwave photonic technology in radar signal processing, researchers from the US DARPA have proposed the concept of modern radar RF front-end based on photonic architecture, focusing on microwave photonic technology with significant influence such as signal generation, distribution and filtering. The core idea is to use microwave photonic technology to physically separate the core part of the complex digital array module from the phased array antenna array, remotely install it in a relatively wide back-end central station, and use optical fiber between the antenna and the back-end central station to achieve remote transmission of microwave signals. Combined with the wavelength division multiplexing of optical transmission, ultra-low loss of optical fiber, lightweight structure and strong electromagnetic compatibility, the low-cost and light-weight microwave photonic transceiver (OTR) antenna layout is more flexible. At the same time, the back-end central station is more tolerant of the structural design of the photonic digital array module, and the problems of weight, heat dissipation, power supply, testing and maintenance will be greatly alleviated. Unfortunately, in the above architecture, the optoelectronic conversion form is subcarrier modulation, and the echo information of the phased array radar remains on the sideband after electro-optical modulation, and its power is much lower than the optical carrier power. The fundamental power of a large number of channels not only does not carry effective information, but also will far exceed the power tolerance of the photodetector after being combined by the wavelength division multiplexer, which can easily cause the photodetector to be oversaturated in power, causing device damage and system abnormality. If the laser output optical power is reduced, the oversaturation of the photodetector can be suppressed, but the performance of the link gain, noise coefficient, etc. will be significantly deteriorated. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a microwave photonic phased array receiving beamforming network, comprising:

[0005] Multiple optical channels, each optical channel includes a laser, a front-end electro-optical intensity modulator, an erbium-doped fiber amplifier and an optical true delay unit connected in sequence; multiple lasers are used to generate multiple optical carriers; multiple front-end electro-optical intensity modulators are used to modulate the downlink radio frequency signals of each front-end electro-optical intensity modulator onto each optical carrier; multiple erbium-doped fiber amplifiers are used to amplify the gain of multiple optical signals; multiple optical true delay units are used to control the delay of multiple optical signals;

[0006] The output ends of the optical true delay units are all connected to the input ends of the wavelength division multiplexer; the output ends of the wavelength division multiplexer are connected to the input ends of the 1×2 optical power splitter, and the output ends of the 1×2 optical power splitter are connected to two optical links, each optical link includes a rear-end electro-optical intensity modulator and a photodetector connected in sequence, and the output ends of the two photodetectors are connected to the input end of the electrical signal differentiator 9; the wavelength division multiplexer is used to synthesize multiple optical signals with different wavelengths into the same optical path; the 1×2 optical power splitter is used to divide the downlink optical signal into two paths with the same power; two rear-end electro-optical intensity modulators are used to modulate their local oscillator signals onto an optical carrier, and the two rear-end electro-optical intensity modulators are respectively a first rear-end electro-optical intensity modulator and a second rear-end electro-optical intensity modulator; two photodetectors are used to demodulate the optical signal into a radio frequency signal; an electrical signal differentiator is used to subtract the two radio frequency signals demodulated by the photodetector, and the differential radio frequency signal enters the subsequent digital signal processing module for processing.

[0007] Furthermore, the laser, the front-end electro-optical intensity modulator, the erbium-doped fiber amplifier, the optical true delay unit and the wavelength division multiplexer are located in the front end of the phased array radar; the 1×2 optical power splitter, the rear-end electro-optical intensity modulator, the photodetector and the electrical signal differentiator are located in the rear end of the phased array radar.

[0008] Furthermore, the multiple lasers have different output light wavelengths, other parameters remain consistent, and the wavelength range of the output light must be consistent with the operating wavelength range of the electro-optic intensity modulator, erbium-doped fiber amplifier, optical true delay unit, wavelength division multiplexer and photodetector.

[0009] Furthermore, the laser is a DFB continuous wave laser with a relative intensity noise RIN≤-150dB / Hz.

[0010] Furthermore, the device parameters of multiple front-end electro-optical intensity modulators remain consistent, the modulation methods all adopt orthogonal bias modulation, and the downlink RF signal is input in push-pull mode.

[0011] Furthermore, the insertion loss of the front-end electro-optical intensity modulator is ≤7dB, and the RF half-wave voltage V π,RF ≤5V, DC half-wave voltage V1 π,DC ≤5V.

[0012] Furthermore, device parameters of the multiple erbium-doped fiber amplifiers remain consistent.

[0013] Furthermore, the amplification gain G of each erbium-doped fiber amplifier to the output optical power of the laser connected thereto is EDFA ≥15dB, noise factor NF EDFA ≤5dB.

[0014] Furthermore, the device parameters of the plurality of optical true delay units are kept consistent; by continuously changing the delay amounts τ1, τ2, ..., τ of the first to nth optical true delay units n , when the delay difference of adjacent optical channels satisfies Δτ=dsinθ / c, align the antenna with the incoming wave direction to achieve beam scanning; where d is the antenna spacing between adjacent optical channels, θ is the incoming wave direction, and c is the speed of light in vacuum.

[0015] Furthermore, the insertion loss of each optical true delay unit is ≤10dB, and the total delay error of each delay state is ≤±10ps.

[0016] Furthermore, the number of multiplexing channels of the wavelength division multiplexer is greater than or equal to the number of wavelengths of the optical carrier of the input optical channel.

[0017] Furthermore, the insertion loss of the wavelength division multiplexer is ≤3.5dB, and the wavelength isolation between adjacent optical channels is ≥25dB.

[0018] Furthermore, the splitting ratio of the 1×2 optical power splitter is 50:50.

[0019] Furthermore, the device parameters of the two rear-end electro-optic intensity modulators are consistent with the device parameters of the front-end electro-optic intensity modulator; the modulation method adopts low bias modulation, and the bias points of the two are symmetrical about the low bias point.

[0020] Furthermore, the range of the DC bias signal S4 received by the first rear-end electro-optical intensity modulator is 2V2 π,DC / 3~5V2 π,DC / 6, single local oscillator signal adopts push-pull mode input, where V2 π,DC is the half-wave voltage of the first rear-end electro-optical intensity modulator 7-1.

[0021] Furthermore, the insertion loss of each rear-end electro-optical intensity modulator is ≤7dB, and the RF half-wave voltage V π,RF ≤5V, DC half-wave voltage V π,DC ≤5V.

[0022] Furthermore, device parameters of the two photodetectors remain consistent.

[0023] Furthermore, each of the photodetectors is a PIN photodetector with a responsivity of ≥0.8A / W.

[0024] Furthermore, the laser, front-end electro-optic intensity modulator, erbium-doped fiber amplifier, optical true delay unit, wavelength division multiplexer, 1×2 optical power splitter, back-end electro-optic intensity modulator and photodetector are all connected by single-mode optical fiber.

[0025] Furthermore, the single-mode optical fiber is a polarization-maintaining single-mode optical fiber.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] At the back end of the network, a single local oscillator can be used to down-convert all received signals, without the need for coherent distribution of clock and local oscillator signals at the front end of the array, which reduces the weight and structural complexity of the array, and can achieve the distance of the array, improving the battlefield survivability and platform adaptability of the phased array; at the back end of the array, low-bias modulation can be used to increase the optical power processing capacity of the entire system, improve the down-conversion efficiency, and optimize the link gain, noise coefficient and other performance; at the same time, by adopting dual parallel modulation differential links at the back end of the array, many useless spectral components can be effectively suppressed, thereby improving the detectability of the down-converted signal and reducing the relative intensity noise of the link; the beamforming and frequency conversion of the RF signal are both performed in the optical domain, and the processable frequency band is very wide, which is suitable for the processing of high-frequency and large-bandwidth signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of a microwave photon downlink beamforming link with n channels according to the first embodiment.

[0029] Figure 2 This is a diagram of the output RF spectrum after the electrical signal differentiator in the 4-channel downlink of Example 1.

[0030] Figure 3 This is a diagram of the output radio frequency spectrum after the photoelectric detector of Example 1.

[0031] Figure 4 4 is a graph showing the relationship between the laser output optical power and the offset angle when the optical power incident on the photodetector is kept unchanged in the simulation of the first embodiment.

[0032] Figure 5 4 is a relationship diagram between the link gain and the offset angle when the optical power incident on the photodetector is kept unchanged in the simulation of the first embodiment.

[0033] The meanings of the symbols in the figure are:

[0034] The first to nth lasers 1-1 to 1-n, the first to nth front-end electro-optical intensity modulators 2-1 to 2-n, the first to nth erbium-doped fiber amplifiers 3-1 to 3-n, the first to nth optical true delay modules 4-1 to 4-n, the wavelength division multiplexer 5, the 1×2 optical power splitter 6, the first back-end electro-optical intensity modulator 7-1, the second back-end electro-optical intensity modulator 7-2, the first photodetector 8-1, the second photodetector 8-2, the electrical signal differentiator 9, the single-mode optical fiber 10, the radio frequency cable 11, the radio frequency signal S1 received by each front-end electro-optical intensity modulator, the DC bias signal S2 received by each front-end electro-optical intensity modulator, the local oscillator signal S3 received by each back-end electro-optical intensity modulator, the DC bias signal S4 received by the first back-end electro-optical intensity modulator, and the DC bias signal S5 received by the second back-end electro-optical intensity modulator. DETAILED DESCRIPTION

[0035] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0037] It is understood that the terms "first", "second", etc. used in this application can be used to describe various elements in this article, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element. Spatial relationship terms such as "under...", "under...", "below...", "under...", "above...", "above", etc. can be used here to describe the relationship between an element or feature shown in the figure and other elements or features. It should be understood that in addition to the orientation shown in the figure, spatial relationship terms also include different orientations of devices in use and operation. For example, if the device in the accompanying drawings is turned over, the element or feature described as "under other elements" or "under it" or "under it" will be oriented to "on" other elements or features. Therefore, the exemplary terms "under..." and "under..." may include upper and lower orientations. In addition, the device may also include other orientations (for example, rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0038] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to another element, or connected to another element through a centering element. In addition, the "connection" in the following embodiments, if there is a transmission of electrical signals or data between the connected objects, should be understood as "electrical connection", "communication connection", etc. When used here, the singular forms of "one", "one" and "said / the" can also include plural forms, unless the context clearly indicates another way. It should also be understood that the terms "include / comprise" or "have" etc. specify the existence of stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the existence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the relevant listed items.

[0039] In view of the poor practicality of the above-mentioned phased array beamforming network based on traditional electronic technology and new photonic technology, the present invention proposes a phased array receiving beamforming network based on low bias modulation and dual parallel differential modulation. By pulling the RF optical fiber far away, the weight and structural complexity of the array are reduced. At the same time, at the back end of the network, a single local oscillator can be used to convert the frequency of all downlink channel signals, without the need for clock local oscillator coherent distribution at the front end of the array; at the back end of the network, low bias modulation can be used to suppress the oversaturation of the photodetector, improve the down-conversion efficiency, and optimize the link gain, noise coefficient and other performance; at the same time, by adopting a dual parallel modulation differential link at the back end of the array, many useless spectrum components can be effectively suppressed, thereby improving the detectability of the down-conversion signal and reducing the relative intensity noise of the link; the beamforming and frequency conversion of the RF signal are both performed in the optical domain, and the processable frequency band is very wide, which is suitable for the processing of high-frequency and large-bandwidth signals.

[0040] The present invention provides a phased array receiving beam forming network based on microwave photon technology, which specifically includes: a plurality of lasers for generating multiple optical carriers, wherein the output wavelength of each laser is different; a plurality of front-end electro-optical intensity modulators for modulating each receiving radio frequency signal onto each optical carrier, wherein the modulation mode adopts orthogonal bias modulation, and the radio frequency input adopts push-pull mode input; a plurality of erbium-doped fiber amplifiers for compensating the loss of each optical signal after optical delay; a plurality of optical true delay units for delay control of multiple optical signals; a wavelength division multiplexer for synthesizing multiple optical signals with different wavelengths into In the same optical path; a 1×2 optical power splitter is used to split the downlink optical signal into two paths with equal power; two electro-optical intensity modulators are used to modulate the local oscillator signal onto the optical carrier, the modulation method adopts low bias modulation, and the bias points of the two electro-optical intensity modulators are set to be symmetrical about the low bias point; two photodetectors are used to demodulate the signal; an electrical signal differentiator is used to subtract the two radio frequency signals demodulated by the photodetectors, and the differential radio frequency signal enters the subsequent digital signal processing module; multiple single-mode optical fibers are used for optical path connection of each device; multiple radio frequency cables are used for transmission of electrical signals.

[0041] Embodiment 1

[0042] This embodiment provides a microwave photonic phased array receiving beamforming network for single beamforming and down-conversion processing of high-frequency, large-bandwidth receiving signals. The general principle block diagram of the receiving network is shown in FIG. Figure 1 As shown, it is divided into two parts: the front end and the back end of the array. Assuming that the link contains n receiving channels, the network includes:

[0043] 1-1, 1-2, ..., 1-n - n lasers, used to generate optical carriers. The output wavelengths of the first to nth lasers 1-1 to 1-n are λ1 to λ n , which are different, adjacent optical wavelengths maintain the same wavelength interval to match the wavelength channel of the wavelength division multiplexer, and other parameters of each laser remain consistent.

[0044] 2-1, 2-2, ..., 2-n - n front-end electro-optical intensity modulators, used to modulate the RF signal S1 received by each front-end electro-optical intensity modulator onto each optical carrier. The device parameters of the first to nth front-end electro-optical intensity modulators 2-1 to 2-n are kept consistent, and the S1 received by each front-end electro-optical intensity modulator adopts push-pull mode input to eliminate phase chirp; the DC bias signal S2 received by each front-end electro-optical intensity modulator adopts orthogonal bias modulation, that is: if the half-wave voltage of the front-end electro-optical intensity modulator is V1 π,DC , then the DC bias signal S2 received by each front-end electro-optical intensity modulator is V1 π,DC / 2, Figure 1The right side of S2 of the middle channel 1 schematically shows the positions of the orthogonal bias points on the transmission functions of the first to nth front-end electro-optic intensity modulators 2 - 1 to 2 - n.

[0045] 3-1, 3-2, ..., 3-n - n erbium-doped fiber amplifiers, used for gain amplification of each optical signal. The device parameters of the first to nth erbium-doped fiber amplifiers 3-1 to 3-n are consistent to ensure the consistency of the gain of each downstream channel.

[0046] 4-1, 4-2, ..., 4-n - n optical true delay modules, used for delay control of each optical signal. The device parameters of the first to nth optical true delay modules 4-1 to 4-n are kept consistent to ensure the consistency of the delay control method and control range of each receiving channel. By changing the delay of each optical true delay unit τ1, τ2, ..., τ n , so that it satisfies the adjacent channel's Δτ=dsinθ / c (where d is the distance between adjacent channel antennas, θ is the incoming wave direction, and c is the speed of light in vacuum), the antenna can be aligned with the incoming wave direction to achieve beam scanning.

[0047] 5——Wavelength division multiplexer, used to combine n optical signals into the same optical path. The number of multiplexed channels is greater than or equal to the number of input optical carriers n.

[0048] The above components 1-1 to 1-n, 2-1 to 2-n, 3-1 to 3-n, 4-1 to 4-n and 5 are located at the front end of the array.

[0049] 6——1×2 optical power splitter, used to split the optical signal output by the wavelength division multiplexer into two paths with equal power.

[0050] 7-1, 7-2 - two rear-end electro-optical intensity modulators, used to modulate the local oscillator signal S3 received by each rear-end electro-optical intensity modulator onto an optical carrier. In the first and second rear-end electro-optical intensity modulators 7-1 and 7-2, the local oscillator signal S3 received by each rear-end electro-optical intensity modulator is input in push-pull mode to eliminate phase chirp; the DC bias signal S4 received by the first rear-end electro-optical intensity modulator and the DC bias signal S5 received by the second rear-end electro-optical intensity modulator are both low-bias modulated, and S4 and S5 are symmetrical about the low bias point, that is: if the half-wave voltage of the first rear-end electro-optical intensity modulator 7-1 is V2 π,DC , then the preferred bias range of the DC bias signal S4 is 2V2 π,DC / 3~5V2 π,DC / 6, S5=2V2 π,DC -S4; Figure 1 The positions of the low bias points on the transmission functions of the first rear-end electro-optical intensity modulator 7-1 and the second rear-end electro-optical intensity modulator 7-2 are schematically shown on the right side of S4 and S5, respectively.

[0051] 8-1, 8-2 - Photodetectors, used to demodulate the light-carrying RF signal into the RF signal.

[0052] 9——Electrical signal differentiator, used to subtract the two RF signals demodulated by the first and second photoelectric detectors 8-1 and 8-2, and the subtracted RF signals enter the subsequent digital signal processing module for processing.

[0053] The above components 6, 7-1, 7-2, 8-1, 8-2 and 9 are located at the rear end of the array.

[0054] 10——Single-mode optical fiber, used for connecting the optical paths between devices, such as Figure 1 The black solid lines between the devices are shown in FIG.

[0055] 11——RF cable, used for transmission of electrical signals, such as Figure 1 As shown by the black dashed line in .

[0056] Taking a 4-channel downlink (n=4) as an example, the Optisystem optical communication link simulation software is used to simulate and analyze the link. In this embodiment, the main parameters of each component in the link are set as follows:

[0057] The output wavelengths λ (frequency f) of the first to fourth lasers 1-1 to 1-4 are 1553.33nm (193THz), 1551.72nm (193.2THz), 1550.12nm (193.4THz) and 1548.51nm (193.6THz), respectively. The output optical power of each laser is P in =32mW, relative intensity noise RIN = -155dB / Hz.

[0058] The first to fourth front-end electro-optic intensity modulators 2-1 to 2-4 and the first to second rear-end electro-optic intensity modulators 7-1 and 7-2 adopt a Mach-Zehnder interference double-arm structure. When a bias voltage is applied, the refractive index of the double-arm material changes due to the electro-optic effect, thereby causing a change in the phase of the transmitted light. After the combined wave, the intensity modulation effect is formed due to interference. The insertion loss of 2-1 to 2-4, 7-1 and 7-2 is set to 5dB (that is, the transmittance at the maximum transmission point is T MZM =10 - 0.5 au), the DC half-wave voltage is V2 π,DC =3V, RF half-wave voltage is V π,RF =3V, the front-end electro-optical intensity modulators 2-1 to 2-4 are set to orthogonal bias, and the DC bias signal S2 received is V1 π,DC / 2=1.5V, the received RF signal S1 is set to broadband small signal input, the frequency is fRF =32-38GHz, frequency interval 2GHz (i.e. 32, 34, 36, 38GHz), signal voltage V RF <V bias / 10; the first and second rear-end electro-optical intensity modulators 7-1 and 7-2 are set to low bias, and the bias points of the two are symmetrical about the low bias point: the DC bias signal S4 received by the first rear-end electro-optical intensity modulator is 2V π,DC / 3=2V, the DC bias signal S5 received by the second rear-end electro-optical intensity modulator is 2V π,DC -S4 = 4V. The local oscillator signal S3 received by each back-end electro-optical intensity modulator is set to a point frequency input with a frequency of f LO =30GHz, signal voltage V LO =0.4au.

[0059] The first to fourth erbium-doped fiber amplifiers 3-1 to 3-4 operate in the linear amplification region and have a fixed output gain, which is set to G EDFA =20dB, noise factor NF EDFA =5dB.

[0060] The first to fourth optical true delay units 4-1 to 4-4 can be composed of a plurality of cascaded 2×2 optical switches. Each pair of 2×2 optical switches is connected by two optical fibers of different lengths, which serve as the base state and the delay state respectively. The optical fiber length can be switched by the "0 / 1" state electrical control switching of the optical switch, thereby realizing the change of the delay state. The cascade of N 2×2 optical switches can realize 2 N The insertion loss is set to 5dB.

[0061] The insertion loss of wavelength division multiplexer 5 is set to 2.5 dB; the insertion loss of 1×2 optical power splitter 6 is set to 0 dB; the parameters of photodetectors 8-1 and 8-2 are the same, and the responsivity is set to r PD =0.8A / W, the dark current is set to 10nA; the electrical signal differentiator 9 is used to subtract the two signals.

[0062] like Figure 3 The figure shows the output RF spectrum of the electrical signal differentiator 9 in the downlink obtained by simulation. The low frequency is the signal f after down conversion. signal -f LO : 2, 4, 6, 8 GHz. In addition, there is also a local oscillator signal f below 100 GHz. LO , the up-converted signal f signal +f LO and the third harmonic signal 3f of the local oscillator LOThe RF signal is filtered out by a low-pass filter and then enters the subsequent digital signal processing unit. The advantages of this microwave photon receiving beamforming network are reflected in the following aspects:

[0063] (1) In terms of link architecture: Traditional digital phased arrays usually adopt an architecture in which the clock and local oscillator are coherently distributed to the front end of the array. The received RF signal must be down-converted to an intermediate frequency with multiple local oscillators in each receiving channel. After analog-to-digital conversion, the downlink data signal is transmitted via optical fiber to the back-end digital receiving and processing unit for processing, which greatly increases the weight, volume, power consumption and structural complexity of the antenna array. The network architecture of the present invention utilizes the optical radio frequency transmission technology to realize the optical fiber extension of the complex processing unit at the array end, and synthesizes the downlink signals of various channels into the same optical path through wavelength division multiplexing, and no clock local oscillator distribution is required at the front end of the array; and only one local oscillator mixing is required at the back end of the extension to realize the down-conversion processing of the received signals of all channels, which greatly saves the array space, reduces the power consumption at the array end, reduces the volume and weight of the array, and improves the battlefield survivability and platform adaptability of the phased array radar array; thanks to the advantages of microwave photon ultra-wideband signal processing, the mixing processing from very high frequency to millimeter wave bands can be realized through only one-stage mixing, and no complex mixing link is required while still ensuring excellent mixing performance.

[0064] (2) The electro-optic intensity modulator at the rear end of the array adopts low bias modulation: In the receiving beamforming network, each optically-carried RF signal contains a relatively high fundamental wave power. After the above signals are combined into one channel through the wavelength division multiplexer, the optical power entering the photodetector is relatively high, especially when there are many downlink channels, it is very easy to exceed the saturation optical power of the photodetector. The excess fundamental wave optical power not only fails to further improve the gain and noise coefficient of the link, but also causes obvious nonlinear effects. Since the fundamental wave does not carry an echo signal, in order to ensure that the gain and noise of the entire network do not deteriorate, it is impossible to avoid saturation at the detector end simply by reducing the laser output. At present, the fundamental wave filtering of dense wavelength division multiplexing optical carrier signals cannot be effectively dealt with by optical domain filtering. The present invention adopts low bias modulation without changing the incident optical power of the laser. Without the aid of a sophisticated and complex optical filtering unit, the optical power entering the photodetector can be returned to the non-saturated region, while ensuring that the link gain and noise coefficient will not deteriorate significantly. The following is a principle explanation of this:

[0065] Considering an intrinsic optical link consisting of a laser, an electro-optic intensity modulator, and a photodetector, the signal gain G and the noise figure NF can be expressed as follows:

[0066]

[0067]

[0068] Among them, r PD is the responsivity of the photodetector, T MZM is the transmittance of the EO intensity modulator biased at the maximum transmission point, T link represents the link loss term, P in The output optical power of the laser Defined as the bias angle of the EO intensity modulator, V π,RF is the RF half-wave voltage of the EO intensity modulator, Z in / Z out For RF input / output matching impedance, P PD is the optical power input to the photodetector, RIN is the relative intensity noise of the laser, R L is the load resistance, q is the unit charge, k is the Boltzmann constant, T is the Kelvin temperature, and V bias is the bias voltage applied to the EO intensity modulator.

[0069] The optical power P input to the photodetector PD The laser output power P in The following relationship exists:

[0070]

[0071] According to formula (3), let P PD When is a fixed value, When gradually increasing from π / 2 (quadrature bias point) and moving toward π (low bias point), Gradually decreases, then P needs to be increased in To maintain P PD constant. Figure 4 It is intuitively shown that when P is maintained PD Unchanged offset angle The laser output power P in For the gain G, formula (1) can be transformed into formula (3):

[0072]

[0073] According to formula (4), when P PD When it remains unchanged, G is proportional to Figure 5 Intuitively shows the gain G and offset angle It can be seen that with the relationship As the laser output power P increases, G will increase accordingly. in There is a limit on G, and G will also have a maximum value limit and cannot increase infinitely. Usually, The value range of is preferably 2π / 3 to 5π / 6.

[0074] From the above analysis, we can get: when P PD When it remains unchanged, G will change with The increase of increases. According to formula (2), in P PD When G remains unchanged, the noise power of each item (the numerator of each item in formula (2)) remains unchanged, while the denominator of each item increases in proportion to G, so the noise figure NF decreases.

[0075] (3) Dual parallel modulation differential detection is adopted at the rear end of the array: At the rear end of the array, by adopting dual parallel modulation differential detection, many useless spectrum components can be effectively suppressed, thereby improving the detectability of the down-converted signal and reducing the relative intensity noise of the link. Figure 2 ), Figure 3 The output RF spectrum after the photodetector 8-1 is shown, that is, the case of a single branch link. Figure 2 and 3 The sources of the spectral components are marked in Figure 2 compared to, Figure 3 There are more DC signal components and original signal components f signal , the second harmonic component of the local oscillator 2f LO , the second harmonic of the local oscillator and the difference frequency component 2f of the original signal LO -f signal and the sum frequency component 2f LO +f signal When the signal bandwidth is large, these useless spectral components will also be broadened, especially near the useful signal f signal -f LO 2f LO -f signal and f signal The components will cause great interference to the subsequent filtering process. The following is a principle explanation of this:

[0076] For the original signal component f signal The DC signal component is divided into two equal power paths by a 1×2 optical power splitter, and then enters a balanced detector after passing through electro-optical intensity modulators 7-1 and 7-2 respectively. The two signals are subtracted, so the original signal component f signal The DC signal components are cancelled at the output of the balanced detector. LO , if the local oscillator signals input to the electro-optic intensity modulators 7-1 and 7-2 are both Asinωt, the output photocurrents after the photodetectors 8-1 and 8-2 are respectively:

[0077]

[0078]

[0079] Among them, P1 and P2 are the input optical powers of the two paths respectively. and are the bias angles of the electro-optic intensity modulators 7-1 and 7-2, respectively, and Then the two photocurrents are subtracted and we get:

[0080]

[0081] Since P1 = P2, the even-order harmonic terms in formula (6) are cancelled, leaving only the odd-order terms. Therefore, the second harmonic component 2f of the local oscillator is LO be offset.

[0082] From the above analysis, we can conclude that: in the dual parallel modulation differential link, due to the original signal component f signal and the second harmonic component 2f of the local oscillator LO is cancelled, then the difference frequency component 2f between the second harmonic of the local oscillator and the original signal LO -f signal and the sum frequency component 2f LO +f signal was also eliminated.

[0083] In summary, the present invention "a microwave photonic phased array receiving beamforming network" can realize the receiving single beamforming and down-conversion processing of high-frequency and large-bandwidth radio frequency signals in the phased array system, and has the following advantages compared with the existing system: the radio frequency optical fiber of the antenna array mixing processing unit is pulled away, and a single local oscillator is used at the rear end of the array to perform optical domain frequency conversion on all downlink channel signals, without the need for coherent distribution of clock and local oscillator signals at the front end of the array, thereby reducing the weight, volume, power consumption and structural complexity of the array; at the rear end of the array, low bias modulation is used to suppress the oversaturation of the photodetector, improve the down-conversion efficiency, and optimize the link gain, noise coefficient and other performance; at the same time, by adopting a dual parallel modulation differential link at the rear end of the array, many useless spectral components can be effectively suppressed, thereby improving the detectability of the down-conversion signal and reducing the relative intensity noise of the link; the beamforming and frequency conversion of the radio frequency signal are both performed in the optical domain, which expands the frequency and bandwidth range of the processable radio frequency signal.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A microwave photonic phased array receiving beamforming network, characterized in that: include: A plurality of optical channels, each optical channel comprising a laser, a front-end electro-optical intensity modulator, an erbium-doped fiber amplifier and an optical true delay unit connected in sequence; A plurality of lasers for generating multi-channel optical carriers; A plurality of front-end electro-optical intensity modulators, used for modulating the radio frequency signal (S1) received by each front-end electro-optical intensity modulator onto each optical carrier; Multiple erbium-doped fiber amplifiers are used for gain amplification of multi-channel optical signals; Multiple optical true delay units for delay control of multi-channel optical signals; The output ends of the optical true delay units are connected to the input ends of the wavelength division multiplexer (5); the output ends of the wavelength division multiplexer (5) are connected to the input ends of the 1×2 optical power splitter (6); the output ends of the 1×2 optical power splitter (6) are connected to two optical links, each optical link includes a rear-end electro-optical intensity modulator and a photodetector connected in sequence, and the output ends of the two photodetectors are connected to the input ends of the electrical signal differentiator (9); the wavelength division multiplexer (5) is used to synthesize multiple optical signals with different wavelengths into the same optical path; the 1×2 optical power splitter (6) ), used to divide the downlink optical signal into two paths with equal power; two rear-end electro-optical intensity modulators, used to modulate the local oscillator signal onto the optical carrier, the two rear-end electro-optical intensity modulators are respectively a first rear-end electro-optical intensity modulator (7-1) and a second rear-end electro-optical intensity modulator (7-2); two photoelectric detectors, used to demodulate the optical signal into a radio frequency signal; an electrical signal differentiator (9), used to subtract the two radio frequency signals demodulated by the photoelectric detector, and the differential radio frequency signal enters the subsequent digital signal processing module for processing.

2. The microwave photonic phased array receiving beamforming network according to claim 1, characterized in that: The laser, front-end electro-optic intensity modulator, erbium-doped fiber amplifier, optical true delay unit and wavelength division multiplexer (5) are located in the front end of the phased array radar; the 1×2 optical power splitter (6), rear-end electro-optic intensity modulator, photoelectric detector and electrical signal differentiator (9) are located in the rear end of the phased array radar.

3. The microwave photonic phased array receiving beamforming network according to claim 2, characterized in that: The multiple lasers have different output light wavelengths respectively, and other parameters remain consistent, and the wavelength range of the output light must be consistent with the operating wavelength range of the electro-optic intensity modulator, erbium-doped fiber amplifier, optical true delay unit, wavelength division multiplexer (5) and photoelectric detector.

4. The microwave photonic phased array receiving beamforming network according to claim 3, characterized in that: The laser is a DFB continuous wave laser, and the relative intensity noise RIN is less than or equal to -150 dB / Hz.

5. The microwave photonic phased array receiving beamforming network according to claim 3, characterized in that: The device parameters of the multiple front-end electro-optic intensity modulators are kept consistent, the modulation methods all adopt orthogonal bias modulation, and the radio frequency signal (S1) received by each front-end electro-optic intensity modulator is input in push-pull mode.

6. The microwave photonic phased array receiving beamforming network according to claim 5, characterized in that: The insertion loss of the front-end electro-optical intensity modulator is ≤7dB, and the RF half-wave voltage V π,RF ≤5V, DC half-wave voltage V1 π,DC ≤5V.

7. The microwave photonic phased array receiving beamforming network according to claim 5, characterized in that: The device parameters of multiple erbium-doped fiber amplifiers remain consistent.

8. The microwave photonic phased array receiving beamforming network according to claim 7, characterized in that: The amplification gain G of each erbium-doped fiber amplifier to the output optical power of the laser connected to it EDFA ≥15dB, noise factor NF EDFA ≤5dB.

9. The microwave photonic phased array receiving beamforming network according to claim 7, characterized in that: The device parameters of multiple optical true delay units are kept consistent; by continuously changing the delay amounts τ1, τ2, ..., τ of the first to nth optical true delay units n , when the delay difference of adjacent optical channels satisfies Δτ=dsinθ / c, align the antenna with the incoming wave direction to achieve beam scanning; where d is the antenna spacing between adjacent optical channels, θ is the incoming wave direction, and c is the speed of light in vacuum.

10. The microwave photonic phased array receiving beamforming network according to claim 9, characterized in that: The insertion loss of each optical true delay unit is ≤10dB, and the total delay error of each delay state is ≤±10ps.

11. The microwave photonic phased array receiving beamforming network according to claim 9, characterized in that: The number of multiplexed channels of the wavelength division multiplexer (5) is greater than or equal to the number of wavelengths of the optical carrier of the input optical channel.

12. The microwave photonic phased array receiving beamforming network according to claim 11, characterized in that: The insertion loss of the wavelength division multiplexer (5) is ≤3.5dB, and the wavelength isolation of adjacent optical channels is ≥25dB.

13. The microwave photonic phased array receiving beamforming network according to claim 12, characterized in that: The splitting ratio of the 1×2 optical power splitter (6) is 50:

50.

14. The microwave photonic phased array receiving beamforming network according to claim 12, characterized in that: The device parameters of the two rear-end electro-optic intensity modulators are consistent with the device parameters of the front-end electro-optic intensity modulator; the modulation mode adopts low bias modulation, and the bias points of the two are symmetrical about the low bias point.

15. The microwave photonic phased array receiving beamforming network according to claim 14, characterized in that: The range of the DC bias signal (S4) received by the first rear-end electro-optical intensity modulator (7-1) is 2V2 π,DC / 3~5V2 π,DC / 6, single local oscillator signal adopts push-pull mode input, where V2 π,DC is the half-wave voltage of the first rear-end electro-optical intensity modulator (7-1).

16. The microwave photonic phased array receiving beamforming network according to claim 15, characterized in that: The insertion loss of each back-end electro-optical intensity modulator is ≤7dB, and the RF half-wave voltage V π,RF ≤5V, DC half-wave voltage V π,DC ≤5V.

17. The microwave photonic phased array receiving beamforming network according to claim 15, characterized in that: The device parameters of the two photodetectors remain consistent.

18. The microwave photonic phased array receiving beamforming network according to claim 17, characterized in that: Each of the photodetectors is a PIN photodetector with a responsivity of ≥0.8A / W.

19. The microwave photonic phased array receiving beamforming network according to claim 17, characterized in that: The laser, front-end electro-optical intensity modulator, erbium-doped fiber amplifier, optical true delay unit, wavelength division multiplexer (5), 1×2 optical power divider (6), back-end electro-optical intensity modulator and photoelectric detector are all connected by single-mode optical fiber (10).

20. The microwave photonic phased array receiving beamforming network according to claim 19, characterized in that: The single-mode optical fiber (10) is a polarization-maintaining single-mode optical fiber.

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