CN116865867A - Frequency conversion synchronous merging method and device for multi-carrier radio frequency signals - Google Patents
Frequency conversion synchronous merging method and device for multi-carrier radio frequency signals Download PDFInfo
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Abstract
The invention discloses a multi-carrier radio frequency signal frequency conversion synchronous merging method in the technical field of microwave photon radio frequency signal processing, which comprises the following steps: the tunable laser drives the tunable optical frequency comb by two paths of light, the two paths of light are combined after frequency conversion of the multi-carrier signals is realized through the coupler, the balance detector and the electric filter, the energy calculating unit and the tunable phase shifter have a communication function, and synchronous alignment is realized on the signals after frequency conversion and combination. The invention also discloses a multi-carrier radio frequency signal frequency conversion synchronous merging device in the technical field of microwave photon radio frequency signals. The multi-carrier radio frequency signal frequency conversion synchronous merging method and device save processing time and realize low-delay synchronization; the integrated realization of signal down-conversion receiving and synchronization is completed, an additional optical delay device is not required to be introduced, the cost is saved, and the optical link insertion loss introduced by the device is avoided.
Description
Technical Field
The invention relates to the technical field of microwave photon radio frequency signal processing, in particular to a multi-carrier radio frequency signal frequency conversion synchronous merging method and device.
Background
The multi-carrier radio frequency signal is a signal with a plurality of radio frequency frequencies as carriers for transmission processing, and has important application value in the fields of microwave photon radars, communication and the like, for example, in coherent radar application, the multi-carrier radio frequency signal can be used for detecting a target, multi-carrier is converted to the same frequency band at a receiving end for superposition processing, when each down-converted radio frequency signal is ensured to have the same phase (namely coherent), coherent accumulation can be carried out on a plurality of frequency echo signals, the signal-to-noise ratio of reception is improved, and parameters such as Doppler frequency shift and the like can be extracted through the phase information of the target echo signal, so that the speed of the target is obtained, and although the echo is converted to the same frequency band for processing, the multi-carrier radio frequency signal comprises response of the target corresponding to the plurality of frequencies, and the defect that the target material has weak reflection to the frequency by utilizing single wave band detection is avoided. In spread spectrum communication application, useful signals can be spread on a wide frequency spectrum formed by multiple carriers, energy is dispersed, when in despreading, despreading is realized by using a despreading code corresponding to a spreading mode, the frequency spectrum is moved back to a baseband, the signals are combined in the same frequency and the same phase, and energy aggregation is completed, so that spread spectrum gain is obtained. It can be seen that the multi-carrier rf signal plays a role in both radar and communication, and the same phase alignment of the multi-carrier rf signal at the receiving end is also critical, which affects the processing gain of the signal, even in extreme cases, when the phases of the unsynchronized signals are opposite, the signal superposition is cancelled, and the processing cannot be performed.
However, in the transmission process of the multi-carrier radio frequency signal, because the signals with different frequencies experience the same transmission time and bring additional different phases, after down-conversion, although the signals are all concentrated at the same frequency, the signals cannot be directly combined due to the additional different phases, in a microwave photon link, an optical frequency comb is used as a multi-wavelength light source with equal frequency intervals and is commonly used for processing the multi-carrier radio frequency signal, and in a multi-carrier radio frequency signal processing system based on the optical frequency comb, two methods are generally used for realizing synchronization after the multi-carrier signal frequency conversion: the first synchronization method adopts each carrier wave to respectively and simultaneously receive in parallel, and then performs phase alignment processing, so that a large amount of hardware resources are consumed, and the low-delay processing effect cannot be achieved; in addition, the second synchronization method adopts a mode of adding a step-adjustable delay line at the local oscillation end to realize delay scanning alignment, however, an additional optical delay line array needs to be introduced, the feedback time is limited, and additional device insertion loss is brought to the optical fiber link. In view of the drawbacks of both synchronization methods, it is necessary to design a method and a device for combining frequency conversion synchronization of multi-carrier radio frequency signals.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a multi-carrier radio frequency signal frequency conversion synchronous merging method and device, which solve the technical problems that in the prior art, the frequency conversion of the multi-carrier radio frequency signal is synchronous, all carriers are adopted to respectively and simultaneously receive in parallel, a large amount of hardware resources are consumed by post-processing for phase alignment, a low-delay processing effect cannot be achieved, an additional optical delay line array is required to be introduced by adopting a local oscillation end to add a step-by-step adjustable delay line, the feedback time is limited, and additional device insertion loss is brought to an optical fiber link, and the phase of each comb tooth is in a linear relation with the serial number in the electro-optical modulation, and the slope is the basic principle for driving the phase of a microwave signal of the comb tooth, so that the phase synchronous alignment of the multi-carrier is realized. The frequency conversion synchronization of the multi-carrier radio frequency signal receiving end can be realized by tuning and driving the initial phase of the electro-optic optical frequency comb microwave source without a huge parallel post-processing hardware module and a tunable delay line array with accurate parameter design.
In order to achieve the above object, the technical scheme of the present invention is as follows:
as one aspect of the present invention, there is provided a multi-carrier radio frequency signal frequency conversion synchronization combining method, including the steps of:
s1, a tunable laser is divided into two paths of optical drive tunable optical frequency combs, wherein one path of optical drive tunable optical frequency comb 1 loads multi-carrier radio frequency signals, and the other path of optical drive tunable electro-optic optical frequency comb 2 is used as a local oscillator optical frequency comb to realize down-conversion on the multi-carrier signals;
s2, the two paths of light are combined after frequency conversion of the multi-carrier signals through the coupler, the balance detector and the electric filter, the energy calculating unit is communicated with the tunable phase shifter, and synchronous alignment is achieved on the signals after frequency conversion and combination.
As a method for frequency conversion synchronization and combination of multi-carrier radio frequency signals in the above aspect of the invention, the step S1 includes the following steps:
s11, a tunable laser provides a single-wavelength laser source with the angular frequency w 0 The phase isThe optical fiber is divided into two paths, wherein one path is used as an optical carrier of the tunable optical frequency comb 1, and the other path is used as an optical carrier of the tunable electro-optic optical frequency comb 2;
s12, the angular frequency interval of the tunable optical frequency comb 1 is w D1 Each comb tooth has a fixed phase difference, which is defined asThe expression of the nth comb tooth output by the tunable optical frequency comb 1 is as follows:
s13, generating a tunable electro-optic frequency comb 2 by adopting an electro-optic modulation method, and driving by a microwave frequency source and a tunable phase shifter;
s14, a receiving antenna receives a multi-carrier radio frequency signal which is transmitted into a receiving system through space, wherein the first carrier frequency of a baseband signal is w RF0 Let its initial phase
S15, the electro-optical modulator is used for loading multi-carrier radio frequency signals and modulating the multi-carrier radio frequency signals on the tunable optical frequency comb 1.
As a method for frequency conversion synchronization and combination of multi-carrier radio frequency signals according to the above aspect of the present invention, the step S13 includes the following steps:
s131, outputting a radio frequency signal by a microwave frequency source, and setting an angular frequency w D2 The tunable phase shifter gives an initial phase to the initial RF signal, set asThen the nth comb output by the tunable electro-optic optical frequency comb 2The tooth expression is:
s132, setting the frequency and the phase of the tunable electro-optic optical frequency comb 2, wherein the delta w is set as follows D ＝w D2 -w D1 Indicating the difference in frequency spacing between the two optical frequency combs,indicating the phase difference of the first comb teeth of the two optical frequency combs.
As a method for frequency conversion synchronization and combination of multi-carrier radio frequency signals according to the above aspect of the present invention, the step S14 includes the following steps:
s141, the multi-carrier radio frequency signal is the sum of a plurality of radio frequency signals with equal frequency intervals starting from a baseband signal, and the multi-carrier frequency
The frequency interval is equal to the difference between the frequency intervals of the tunable optical frequency comb 1 and the tunable electro-optical frequency comb 2;
s142, when the multi-carrier radio frequency signals are not transmitted spatially, the initial phases of the multi-carrier radio frequency signals are the same, and the expression is as follows:
as a method for frequency conversion synchronization and combination of multi-carrier radio frequency signals according to the above aspect of the present invention, the step S15 includes the following steps:
s151, considering additional delay delta tau brought by space transmission to a multi-carrier signal, after modulation, the nth comb tooth expression output by the tunable optical frequency comb 1 is:
s152, taking the real parts of the formula (2) and the formula (4) respectively, wherein the expression of the output signal of the tunable electro-optic frequency comb 2 and the expression of the n-th comb tooth of the tunable optical frequency comb 1 after the multi-carrier signal is loaded are specifically as follows:
as a method for frequency conversion synchronization and combination of multi-carrier radio frequency signals in the above aspect of the invention, the step S2 includes the following steps:
s21, realizing beat frequency of two paths of light through a coupler, realizing photoelectric conversion by a balanced photoelectric detector, and inputting two paths of light signals A of the photoelectric detector 1 ，A 2 The method comprises the following steps:
i.e.The photocurrent output by the balanced photodetector is: i (t) ≡A 1 A 1 * -A 2 A 2 * ；
S22 due to w RF0 +nΔw D +nw D1 ＝w RF0 +nw D2 Only the signals of the mutual beat frequency of the comb teeth with the same serial numbers in the modulated tunable optical frequency comb 1 and the tunable electro-optical frequency comb 2 are reserved, and the current I' (t) output by the electric filter is calculated as follows:
s23, inputting I' (t) into an energy calculating unit to calculate energy, and simultaneously, changing the phase value of the tunable phase shifter in a certain step.
As a method for frequency conversion synchronization and combination of multi-carrier radio frequency signals according to the above aspect of the present invention, the step S23 includes the following steps:
s231, considering different photocurrent components of the beat frequency contribution of adjacent comb teeth in I' (t):
phase difference of the twoWherein Deltaw D And Δτ is a quantification;
s232 by tuningWhen the phase difference of adjacent comb teeth meets the integral multiple of 2 pi, (8) is expressed as:
at this time, coherent superposition of each channel is realized, the maximum value is obtained through the judgment of the energy calculating unit, and the maximum value is fed back to the tunable phase shifter, and the phase value at this time is fixed.
As another aspect of the present invention, there is provided a multi-carrier radio frequency signal frequency conversion synchronization combining apparatus, including:
the tunable laser is used for providing a single-wavelength laser source and is divided into two paths, wherein one path is used as an optical carrier of the tunable optical frequency comb 1, and the other path is used as an optical carrier of the tunable electro-optic optical frequency comb 2; and
the tunable optical frequency comb 1 takes the frequency of a tunable laser as the center to form an optical frequency comb with equal frequency intervals on a frequency spectrum, and the optical frequency comb is used as a signal optical frequency comb to bear multi-carrier signals; and
a receiving antenna for receiving a multi-carrier radio frequency signal transmitted spatially to the system; and
an electro-optical modulator for loading the multi-carrier radio frequency signal on the tunable optical frequency comb 1; and
the tunable electro-optic optical frequency comb 2 is generated by an electro-optic modulation method, and takes the frequency of a tunable laser as the center to form an optical frequency comb with equal frequency intervals on a frequency spectrum as a local oscillator optical frequency comb; and
the microwave frequency source is used for driving the tunable electro-optic optical frequency comb 2, and the frequency of the microwave frequency source determines the frequency interval of the tunable electro-optic optical frequency comb 2; and
the tunable phase shifter has a communication function, realizes tuning in a certain step, and changes the comb tooth phase of the tunable electro-optic optical frequency comb 2.
As a method for a multi-carrier radio frequency signal frequency conversion synchronization combining device according to the above aspect of the present invention, the method further includes:
the coupler is used for combining signals of the tunable optical frequency comb 1 and the tunable optical frequency comb 2; and
the balanced photoelectric detector is used for realizing photoelectric conversion on signals output by the coupler; and
the electric filter is used for filtering the output current of the balance detector, and the bandwidth of the electric filter is consistent with the baseband bandwidth of the multi-carrier radio frequency signal; and
an energy calculation unit for calculating the energy of the output signal of the electrical filter and capable of communicating with the tunable phase shifter.
By adopting the technical scheme, the invention has the following advantages:
the invention provides a frequency conversion synchronous merging method and device for multi-carrier radio frequency signals, which utilize the basic principle that the phase of each comb tooth is in a linear relation along with the serial number in electro-optic modulation, the slope is used for driving the phase of each microwave signal, the same time synchronous alignment of multi-carriers is realized in a photon analog domain, a huge and parallel post-processing hardware module is not needed, an adjustable optical delay line array with accurate parameter design is also not needed, the frequency conversion synchronization of a multi-carrier radio frequency signal receiving end can be realized by tuning and driving the initial phase of an electro-optic frequency comb microwave source, the digital processing is not needed after each carrier is respectively received, the complexity of the system is reduced, the processing time is saved, and the synchronization with low delay is realized; the integrated realization of signal down-conversion receiving and synchronization is completed, an additional optical delay device is not required to be introduced, the cost is saved, and the optical link insertion loss introduced by the device is avoided.
Drawings
Fig. 1 is a system block diagram of a multi-carrier radio frequency signal frequency conversion synchronous combining device of the invention;
fig. 2 is a schematic diagram of the evolution of the spectrum and phase of each link signal in the method for frequency conversion synchronization combination of multi-carrier radio frequency signals according to the present invention.
Detailed Description
In the following detailed description of the embodiments of the present invention, reference is made to the accompanying drawings, in which it is to be noted that, in this document, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Fig. 1 shows a system block diagram of a multi-carrier radio frequency signal frequency conversion synchronization combining device of the present invention; the device for frequency conversion synchronization and combination of multi-carrier radio frequency signals specifically shown in fig. 1 comprises a tunable single-frequency laser 100, a tunable optical frequency comb 1140, a tunable electro-optic optical frequency comb 2110, a microwave frequency source 130, a tunable phase shifter 120, a receiving antenna 160, an electro-optic modulator 150, a coupler 170, a balanced photodetector 180, an electric filter 190 and an energy calculation unit 200.
The tunable laser 100 provides a single-wavelength laser source, which is divided into two paths, one path being an optical carrier of the tunable optical frequency comb 1140 and the other path being an optical carrier of the tunable electro-optical frequency comb 2110.
The tunable optical frequency comb 1140 may be generated by using an electro-optical modulation method, or may be generated by other manners such as microcavity, and uses the frequency of the tunable laser 100 as the center to form an optical frequency comb with equal frequency intervals on the frequency spectrum, and the optical frequency comb is used as a signal optical frequency comb to carry multi-carrier signals.
The receiving antenna 160 receives the multicarrier radio frequency signal transmitted spatially to the system and is loaded onto the tunable optical frequency comb 1 by the electro-optical modulator 150.
The tunable electro-optic optical frequency comb 2110 is generated by an electro-optic modulation method, and uses the frequency of the tunable laser 100 as the center to form an optical frequency comb with equal frequency intervals in the frequency spectrum as a local oscillator optical frequency comb. The frequency spacing of the tunable electro-optic frequency comb 2110 differs from the frequency spacing of the tunable optical frequency comb 1140 by an amount equal to the frequency spacing of the multi-carrier radio frequency signal. The comb tooth phase of each optical frequency comb is positively correlated with the phase of the drive of its tunable phase shifter 120, increasing by equal factors with increasing comb tooth number. The microwave frequency source 130 drives the tunable electro-optic optical frequency comb 2, the frequency of which determines the frequency spacing of the tunable electro-optic optical frequency comb 2110. The tunable phase shifter 120 has a communication function, and can realize tuning in a certain step, and change the comb tooth phase of the tunable electro-optic frequency comb 2110.
The coupler 170 combines the signals of the tunable optical frequency comb 1 and the tunable optical frequency comb 2, and sends the signals into the balanced photodetector 180 to realize photoelectric conversion. The electrical filter 190 filters the output current of the photodetector 180 with a bandwidth that corresponds to the baseband bandwidth of the multi-carrier radio frequency signal. The energy calculation unit 200 calculates the energy of the output signal of the electrical filter 190 and is capable of communicating with the tunable phase shifter 120. When the energy calculation unit 200 obtains the maximum energy, the communication command is sent to the tunable phase shifter 120 to stop the phase tuning, and at this time, the electric filter 190 outputs the maximum output obtained by the signal, and the multi-carrier signals are synchronously combined after frequency conversion.
Fig. 2 shows an evolution diagram of the spectrum and phase of each link signal in the multi-carrier radio frequency signal frequency conversion synchronous combining method of the invention; FIG. 2 (a) is a diagram of the frequency spectrum and phase of a tunable optical frequency comb 1140; fig. 2 (b) is a schematic diagram of the spectrum and phase of the initial multi-carrier signal; fig. 2 (c) is a schematic diagram of the spectrum and phase of a multicarrier signal after spatial transmission; fig. 2 (d) is a schematic diagram of the frequency spectrum of the tunable optical frequency comb 1140 after loading the multi-carrier rf signal; FIG. 2 (e) is a schematic diagram of the frequency spectrum and phase of a tunable electro-optic optical frequency comb 2110; fig. 2 (f) is a coherent superposition of multiple carriers after down-conversion synchronization.
The frequency conversion synchronous merging method of the multi-carrier radio frequency signals comprises the following steps:
S1A tunable laser 100 provides a single wavelength laser source at a frequency (angular frequency) w 0 The phase isIt is divided into two paths, one path is used as the optical carrier of the tunable optical frequency comb 1140 and the other path is used as the optical carrier of the tunable electro-optical frequency comb 2110.
Wherein, S1 comprises the following steps:
s11, a tunable laser provides a single-wavelength laser source with the angular frequency w 0 The phase isThe optical fiber is divided into two paths, wherein one path is used as an optical carrier of the tunable optical frequency comb 1, and the other path is used as an optical carrier of the tunable electro-optic optical frequency comb 2;
s12, the tunable optical frequency comb 1140 can be produced by adopting an electro-optical modulation method, or can be produced by other modes such as microcavity, and the frequency (angular frequency) interval is w D1 Each comb tooth has a fixed phase difference, which is defined asThe spectrum and phase diagram are shown in fig. 2 (a), and the expression of the nth comb teeth output by the tunable optical frequency comb 1140 is:
s13, the tunable electro-optic frequency 2110 is generated by adopting an electro-optic modulation method and is driven by a microwave frequency source 130 and a tunable phase shifter 120.
S13 comprises the following steps:
s131, the tunable electro-optic frequency comb 2110 is generated by adopting an electro-optic modulation method, and is driven by a tunable microwave frequency source 130 and a tunable phase shifter 120, wherein the tunable microwave frequency source 130 outputs a radio frequency signal, and the frequency (angular frequency) is set as w D2 The tunable phase shifter 120 imparts an initial phase to the initial RF signal, set toThe nth comb tooth output by the tunable optical frequency comb 1140 has the following expression:
that is, each optical frequency comb of the electro-optical modulation optical frequency comb obtains comb tooth phase proportional to the product of the comb tooth serial number and the phase of the driving microwave signal.
S132, the frequency spectrum and the phase diagram of the tunable electro-optic frequency comb 2110 are specifically shown in fig. 2 (e), wherein the delta w is given by D ＝w D2 -w D1 Representing the difference in frequency spacing between the two optical frequency combs, which should be equal to the frequency spacing of the multi-carrier radio frequency signal,for the phase difference of the first comb teeth of the two optical frequency combs, the tunable phase shifter can be changed +.>Thus (S)>Is tunable.
S14, the receiving antenna 160 receives the multicarrier RF signal transmitted into the receiving system through space, as shown in FIG. 2 (c), wherein the first carrier frequency in the baseband signal is w RF0 (the baseband signal can be in dot frequency or linear frequency modulation format) in order to derive the formula, only the first carrier frequency (angular frequency) w is taken RF0 For example, let its initial phase be
S14 comprises the following steps:
s141, taking a baseband signal as an initial multi-carrier radio frequency signal, and taking the sum of a plurality of radio frequency signals with equal frequency intervals as shown in fig. 2 (b);
s142, when the multi-carrier radio frequency signals are not transmitted spatially, the initial phases of the multi-carrier radio frequency signals are the same, and the expression is as follows:
s15, the electro-optical modulator 150 is used for loading a multi-carrier radio frequency signal and modulating the multi-carrier radio frequency signal on the tunable optical frequency comb 1.
S15 comprises the following specific steps:
s151, the electro-optical modulator 150 is used for loading a multi-carrier radio frequency signal, modulating the multi-carrier radio frequency signal on the tunable optical frequency comb 140, and considering the additional delay delta tau brought by space transmission to the multi-carrier signal, after modulation, the n-th comb tooth expression output by the electro-optical modulator is:
s152, a spectrum diagram of the tunable optical frequency comb 1140 loaded multi-carrier radio frequency signals is shown in fig. 2 (d), and real parts of formulas (2) and (4) are taken, specifically as follows:
s2, the two paths of light are combined after frequency conversion of the multi-carrier signals is achieved through the coupler, the balance photoelectric detector and the electric filter, the energy calculating unit is communicated with the tunable phase shifter, and synchronous alignment is achieved on the signals after frequency conversion and combination.
S2 comprises the following steps:
s21, the beat frequency of the two paths of light is realized through the coupler 170, the photoelectric conversion is realized by the photoelectric detector 180, and the two paths of light signals A of the photoelectric detector 180 are input 1 ，A 2 The method comprises the following steps:
i.e.The photocurrent output by the balanced photodetector is: i (t) ≡A 1 A 1 * -A 2 A 2 * ；
S22, the bandwidth of the electric filter 190 is larger than or equal to the bandwidth of the baseband signal and smaller than the difference between the frequency intervals of the tunable optical frequency comb 1 and the tunable electro-optical frequency comb 2. Then due to w RFO +nΔw D +nw D1 ＝w RF0 +nw D2 Only the signals of the mutual beat frequency of the comb teeth with the same serial numbers in the modulated tunable optical frequency comb 1 and the tunable electro-optical frequency comb 2 are reserved, and the current I' (t) output by the electric filter is calculated as follows:
i.e. I' (t) is a superposition of a series of signals with equal frequency but different phases, and the series of signals with the same frequency can realize coherent superposition of the same frequency only when the phases of the signals are completely equal or the phases of the signals are different by an integer multiple of 2 pi, so as to obtain maximum energy, otherwise, the energy is weakened, and even the signals may be destructively superimposed.
S23, inputting I' (t) into an energy calculating unit to calculate energy, and simultaneously, changing the phase value of the tunable phase shifter in a certain step.
Wherein, S23 comprises the following specific steps:
s231, I' (t) is input to the energy calculation unit 200 to calculate its energy, and at the same time, the tunable phase shifter 120 changes its phase value in steps. Consider the different photocurrent components of the adjacent comb teeth in I' (t) contributing to the beat frequency:
phase difference of the twoWherein Deltaw D And Deltaτ is the quantification, < >>Controlled by the tunable phase shifter 120 is a variable.
S232. thus, it is possible to tuneWhen the phase difference between the two is made to satisfy the integral multiple of 2 pi, the formula (8) can be expressed as:
at this time, coherent superposition of each channel is realized, and the maximum value is obtained through judgment of the energy calculation unit 200 and fed back to the tunable phase shifter 120, and the phase value at this time is fixed, that is, phase synchronization after multi-carrier frequency conversion is realized, as shown in fig. 2 (f).
Finally, it is pointed out that while the invention has been described with reference to a specific embodiment thereof, it will be understood by those skilled in the art that the above embodiments are provided for illustration only and not as a definition of the limits of the invention, and various equivalent changes or substitutions may be made without departing from the spirit of the invention, therefore, all changes and modifications to the above embodiments shall fall within the scope of the appended claims.
Claims (9)
1. The frequency conversion synchronous merging method of the multi-carrier radio frequency signals is characterized by comprising the following steps of:
s1, a tunable laser is divided into two paths of optical drive tunable optical frequency combs, wherein one path of optical drive tunable optical frequency comb 1 loads multi-carrier radio frequency signals, and the other path of optical drive tunable electro-optic optical frequency comb 2 is used as a local oscillator optical frequency comb to realize down-conversion on the multi-carrier signals;
s2, the two paths of light are combined after being subjected to frequency conversion through the coupler, the balance detector and the electric filter, the energy calculating unit is in communication interaction with the tunable phase shifter, and synchronous alignment is achieved on the signals after frequency conversion and combination.
2. The method for frequency-conversion synchronous combination of multi-carrier radio frequency signals according to claim 1, wherein S1 comprises the steps of:
s11, a tunable laser provides a single-wavelength laser source with the angular frequency w 0 The phase isThe optical fiber is divided into two paths, wherein one path is used as an optical carrier of the tunable optical frequency comb 1, and the other path is used as an optical carrier of the tunable electro-optic optical frequency comb 2;
s12, the angular frequency interval of the tunable optical frequency comb 1 is w D1 Each comb tooth has a fixed phase difference, which is defined asThe expression of the nth comb tooth output by the tunable optical frequency comb 1 is as follows:
s13, generating a tunable electro-optic frequency comb 2 by adopting an electro-optic modulation method, and driving by a microwave frequency source and a tunable phase shifter;
s14, a receiving antenna receives a multi-carrier radio frequency signal which is transmitted into a receiving system through space, wherein the first carrier frequency of a baseband signal is w RF0 Let its initial phase
S15, the electro-optical modulator is used for loading multi-carrier radio frequency signals and modulating the multi-carrier radio frequency signals on the tunable optical frequency comb 1.
3. The method for frequency-conversion synchronization combining of multi-carrier rf signals according to claim 2, wherein said S13 comprises the steps of:
s131, outputting a radio frequency signal by a microwave frequency source, and setting an angular frequency w D2 The tunable phase shifter gives an initial phase to the initial RF signal, set asThe expression of the nth comb tooth output by the tunable electro-optic frequency comb 2 is:
s132, setting the frequency and the phase of the tunable electro-optic optical frequency comb 2, wherein the delta w is set as follows D ＝w D2 -w D1 Indicating the difference in frequency spacing between the two optical frequency combs,indicating the phase difference of the first comb teeth of the two optical frequency combs.
4. A method of frequency-conversion synchronous combining of multi-carrier radio frequency signals according to claim 3, wherein said S14 comprises the steps of:
s141, taking a multi-carrier radio frequency signal as a sum of a plurality of radio frequency signals with equal frequency intervals starting from a baseband signal, wherein the multi-carrier frequency interval is equal to the difference between the frequency intervals of the tunable optical frequency comb 1 and the tunable electro-optical frequency comb 2;
s142, when the multi-carrier radio frequency signals are not transmitted spatially, the initial phases of the multi-carrier radio frequency signals are the same, and the expression is as follows:
5. the method for frequency-conversion synchronization combining of multi-carrier rf signals according to claim 4, wherein S15 comprises the steps of:
s151, considering additional delay delta tau brought by space transmission to a multi-carrier signal, after modulation, the expression of the n-th comb tooth of the tunable optical frequency comb 1 after the multi-carrier signal is loaded is:
s152, taking the real parts of the formula (2) and the formula (4) respectively, wherein the expression of the output signal of the tunable electro-optic frequency comb 2 and the expression of the n-th comb tooth of the tunable optical frequency comb 1 after the multi-carrier signal is loaded are specifically as follows:
6. the method for frequency-conversion synchronization combining of multi-carrier rf signals according to claim 5, wherein S2 comprises the steps of:
s21, realizing beat frequency of two paths of light through a coupler and realizing photoelectricity by a balanced photoelectric detectorTwo paths of optical signals A of a conversion and input balance photoelectric detector 1 ，A 2 The method comprises the following steps:
i.e.The photocurrent output by the balanced photodetector is: i (t) ≡A 1 A 1 * -A 2 A 2 * ；
S22 due to w RF0 +nΔw D +nw D1 ＝w RF0 +nw D2 Only the signals of the mutual beat frequency of the comb teeth with the same serial numbers in the modulated tunable optical frequency comb 1 and the tunable electro-optical frequency comb 2 are reserved, and the current I' (t) output by the electric filter is calculated as follows:
s23, inputting I' (t) into an energy calculating unit to calculate energy, and simultaneously, changing the phase value of the tunable phase shifter in a certain step.
7. The method for frequency-conversion synchronization combining of multi-carrier rf signals according to claim 6, wherein S23 comprises the steps of:
s231, considering different photocurrent components of the beat signal contribution of adjacent comb teeth in I' (t):
phase difference of the twoWherein Deltaw D And Δτ is a quantification;
s232 by tuningWhen the phase difference of adjacent comb teeth meets the integral multiple of 2 pi, (8) is expressed as:
at this time, coherent superposition of each channel is realized, the maximum value is obtained through the judgment of the energy calculating unit, and the maximum value is fed back to the tunable phase shifter, and the phase value at this time is fixed.
8. A multi-carrier radio frequency signal frequency conversion synchronization combining device, comprising:
the tunable laser is used for providing a single-wavelength laser source and is divided into two paths, wherein one path is used as an optical carrier of the tunable optical frequency comb 1, and the other path is used as an optical carrier of the tunable electro-optic optical frequency comb 2; and
the tunable optical frequency comb 1 takes the frequency of a tunable laser as the center to form an optical frequency comb with equal frequency intervals on a frequency spectrum, and the optical frequency comb is used as a signal optical frequency comb to bear multi-carrier signals; and
a receiving antenna for receiving a multi-carrier radio frequency signal transmitted spatially to the system; and
an electro-optical modulator for loading the multi-carrier radio frequency signal on the tunable optical frequency comb 1; and
the tunable electro-optic optical frequency comb 2 is generated by an electro-optic modulation method, and takes the frequency of a tunable laser as the center to form an optical frequency comb with equal frequency intervals on a frequency spectrum as a local oscillator optical frequency comb; and
the microwave frequency source is used for driving the tunable electro-optic optical frequency comb 2, and the frequency of the microwave frequency source determines the frequency interval of the tunable electro-optic optical frequency comb 2; and
the tunable phase shifter has a communication function, realizes tuning in a certain step, and changes the comb tooth phase of the tunable electro-optic optical frequency comb 2.
9. The apparatus for frequency translating synchronous combining of multi-carrier radio frequency signals according to claim 8, further comprising:
the coupler is used for combining signals of the tunable optical frequency comb 1 and the tunable optical frequency comb 2; and
the balanced photoelectric detector is used for realizing photoelectric conversion on signals output by the coupler; and
the electric filter is used for filtering the output current of the balance detector, and the bandwidth of the electric filter is consistent with the baseband bandwidth of the multi-carrier radio frequency signal; and
an energy calculation unit for calculating the energy of the output signal of the electrical filter and capable of communicating with the tunable phase shifter.
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