CN108802503B - Multi-channel frequency conversion data compensation system and method for solar radio observation system - Google Patents
Multi-channel frequency conversion data compensation system and method for solar radio observation system Download PDFInfo
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Abstract
The invention discloses a multichannel frequency conversion data compensation system and method of a solar radio observation system based on FPGA, which receives data of each channel of a frequency conversion card and converts the data into digital data; respectively carrying out FFT operation on the digital data of each channel to obtain frequency domain data of each channel; measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between channels of the frequency conversion card, and calculating the correction coefficient of each frequency point; and correcting the frequency point data of each channel by using the correction coefficient. According to the invention, by measuring the difference of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel of the mixer, the FPGA compensates the amplitude-frequency characteristic and the phase-frequency characteristic of each frequency point, the inconsistent error of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel is reduced, the amplitude-frequency characteristic of each frequency point is compensated to be an ideal and consistent curve on a computer, and the measurement accuracy of the solar radio observation system is improved.
Description
Technical Field
The invention relates to the field of data compensation, in particular to a multi-channel frequency conversion data compensation system and method of a solar radio observation system based on an FPGA.
Background
The wavelength of solar radio radiation is generally in the decimeter-ten meter band (frequency MHz to GHz). The solar radio radiation in decimeter-decameter wave frequency band is characterized by high dynamic range, signal outbreak with the solar activity and abundant morphological expression on frequency spectrum. The related signals are all from high-energy electrons accelerated by solar activity, and the radiation mechanism is made of plasma radiation, bremsstrahlung, gyrus, pulse-luster radiation and other mechanisms, and is related to the process of flare-reconnection or coronage substance ejection-shock wave. A large number of observation stations are built at home and abroad to observe solar radio, and the condition of part of low-frequency observation stations is counted in a graph 1.
AMATERAS, developed in 2010 by Tohoku university, japan (Iwai et al, 2012). The AMATERAS observation frequency range is 150-500MHz, the time and frequency resolution is as high as 10ms and 61kHz, and the signals are polarized in left and right directions. The receiver adjusts the left-handed radio signal of 100-plus-500 MHz to 550-plus-950 MHz by a frequency mixing circuit with 1050MHz local oscillation, and synthesizes the signal with the right-handed signal of 100-plus-500 MHz to obtain a signal, and digitalizes the signal by using an AD to obtain the solar radio frequency spectrum.
The Yunnan astronomical stage of the Chinese academy of sciences, 11m parabolic antenna was sampled in 2011 to construct a solar meter wave radio receiving system, and the receiving frequency range is as follows: 70-700MHz, frequency resolution 200KHz, time resolution up to 2 ms. The receiver utilizes AD9430 with a sampling rate of 210Msps to carry out AD conversion, the single-channel analog signal bandwidth of the frequency spectrograph is 87.5MHz, the bandwidth of 8 channels is 700MHz, a low-noise amplifier and a filter are sampled at the front end of each channel to condition the signal, then the signal is modulated to a required intermediate frequency signal of 110-197.5MHz after 2 times of frequency conversion, and 16 mixing circuits are adopted for carrying out signal processing.
The GBSRBS observation station built in 2004 in USA has observation frequency range from 10MHz to 3000MHz, which is realized by 3 receivers, and LPDA antenna is sampled at 10-80 MHz; a 7-meter parabolic antenna is adopted at 80-850 MHz; the 800-3000MHz band employs a 3 meter parabolic antenna. These receivers all require a frequency conversion section to achieve frequency conversion to within the ADC bandwidth for acquisition.
The DuQ F adopts 2 paths of 1.25Gsps sampling rate, a 12-bit ADC acquisition card and 500MHz analog bandwidth, realizes the observation of a frequency spectrograph for 150-plus-500 MHz solar radio signals, does not need a frequency mixer, and reduces the sensitivity when high time resolution is caused due to the adoption of periodic quantitative data acquisition. Therefore, the Du Q F also designs a solar radio receiver with higher index, and adopts 4-path sampling rate of 500Msps and 14-bit ADC converter to receive 2-path solar radio signals with 150-channel sampling rate of 500 MHz. Each signal is divided into two segments of 150-325MHz and 325-500MHz, i.e. 350M bandwidth is divided into two 175M sub-channels. In order to avoid 2 frequency multiplication interference and frequency band superposition interference, two sub-channels are moved to 875M intermediate frequency through a variability card and then sent to an ADC for collection, a flow chart of a parabolic antenna signal is shown as 2, an antenna outputs horizontal and vertical signals, the horizontal and vertical signals are amplified through a low-noise amplifier and conditioned through a filter circuit respectively, each signal is moved to 787.5-962.5MHz intermediate frequency band through a circuit of a frequency mixing circuit card, the signals are converted into digital signals through the ADC respectively, then FFT operation is carried out through an FPGA, polarization synthesis left-handed rotation and right-handed rotation are carried out in a frequency domain, and other processing is carried out.
Although the ADC has higher and higher sampling rate and larger acquisition signal bandwidth, the frequency conversion circuit is a circuit which must be used by a broadband receiver and is smaller relative to the bandwidth of a solar radio signal to be observed. The frequency conversion circuit is an analog circuit, various device parameters have dispersion and the circuit design is asymmetric, amplitude-frequency characteristics and phase-frequency characteristics of different frequency points of each channel are different in the process of processing signals in a high-frequency bandwidth, and the amplitude-frequency characteristics and the phase-frequency characteristics of the channels are also inconsistent, so that a receiver generates a large error, particularly, the channel difference influences the size change of a left-handed signal and a right-handed signal output by solar radio circular polarization synthesis, and the measurement accuracy of polarization characteristic parameters is influenced. The polarization characteristic is a very important parameter of solar radio, is closely related to a radiation mechanism, can directly reflect the plasma parameter of a radiation source region and the change condition of a magnetic field, can provide energy release, particle acceleration and magnetic field information, and is also related to the transmission process of electromagnetic waves, such as the electromagnetic waves are subjected to refraction and scattering of corona or mode coupling so as to cause depolarization effect. Due to the inconsistency of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel, a great error occurs in the left-right-turn signal output by the receiver, and some signals can cause the result of a south-beam north track to researchers. The design of the circuit can be modified by screening the parameters of the components of the frequency conversion circuit, so that the errors can be reduced, but the errors are completely overcome, the ideal consistency among channels is difficult, and the cost is multiplied.
In summary, for the asymmetry of the frequency conversion circuit in the prior art, in the process of processing a signal in a high-frequency bandwidth, amplitude-frequency characteristics and phase-frequency characteristics of different frequency points of each channel are different, and the amplitude-frequency characteristics and the phase-frequency characteristics of the channels are also inconsistent, which may cause a large error of a receiver, and particularly, the channel differences affect the size change of left-handed and right-handed signals output by solar radio circular polarization synthesis, which affects the accuracy of polarization characteristic parameter measurement, and an effective solution is not yet available.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a multichannel frequency conversion data compensation system and method of a solar radio observation system based on an FPGA (field programmable gate array). by measuring the difference of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel of a mixer, the FPGA compensates the amplitude-frequency characteristic and the phase-frequency characteristic of each frequency point, the non-uniform error of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel is reduced, the amplitude-frequency characteristic of each frequency point is compensated into an ideal and consistent curve on a computer, and the measurement accuracy of the solar radio observation system is improved.
The technical scheme adopted by the invention is as follows:
the invention aims to provide a multi-channel frequency conversion data compensation method for a solar radio observation system, which comprises the following steps:
receiving data of each channel of the frequency conversion card and converting the data into digital data;
respectively carrying out FFT operation on the digital data of each channel to obtain frequency domain data of each channel;
measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between channels of the frequency conversion card, and calculating the correction coefficient of each frequency point;
and correcting the frequency point data of each channel by using the correction coefficient.
Further, the method for measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between the channels of the frequency conversion card comprises the following steps:
the sinusoidal signal source is divided into two paths of constant-amplitude in-phase signals through the power divider, and the two paths of the constant-amplitude in-phase signals are respectively input into two channels of the frequency conversion card;
performing analog-to-digital conversion on the two paths of constant-amplitude in-phase signals through two channels of the ADC to obtain time domain signals;
performing FFT operation on the time domain signals, converting the time domain signals of the two channels into frequency domain signals, and calculating the amplitude ratio between the data of the two channels to obtain the error of the amplitude-frequency characteristic between the channels; and calculating the angle difference between the two channel data to obtain the error of the inter-channel phase-frequency characteristic.
Further, the calculation method of the correction coefficient is as follows:
and solving cosine values and sine values corresponding to angles between the frequency point data of the two channels, and multiplying the cosine values and the sine values by the amplitude ratio between the frequency point data of the two channels to respectively obtain real parts and imaginary parts of the correction coefficients.
Further, the method for correcting the frequency point data of each channel comprises the following steps:
and in the frequency domain, multiplying each frequency point data of each channel by the corresponding correction coefficient respectively to obtain the compensated frequency point data.
The second purpose of the invention is to provide a system for realizing the data compensation method of the multi-channel frequency conversion of the solar radio observation system, which comprises a frequency conversion card, an ADC converter, a computer and an FPGA;
the ADC converter is connected with the variable frequency card and is configured to: receiving data of each channel of the frequency conversion card, converting the data into digital data, and uploading the digital data to the FPGA;
the FPGA configured to: respectively carrying out FFT operation on the digital data of each channel to obtain frequency domain data of each channel, and uploading the frequency domain data to a computer; receiving a correction coefficient sent by a computer, and correcting the frequency point data of each channel;
and the computer is configured to measure the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between the channels of the frequency conversion card, calculate the correction coefficient of each frequency point and send the correction coefficient to the FPGA.
The sinusoidal signal source is divided into two paths of constant-amplitude in-phase signals through the power divider, and the two paths of constant-amplitude in-phase signals are respectively input into two channels of the frequency conversion card; performing analog-to-digital conversion on the two paths of constant-amplitude in-phase signals through two channels of the ADC, and uploading the converted time domain signals to the FPGA; the FPGA carries out FFT operation on the time domain signals and transforms the time domain signals of the two channels to frequency domain signals.
Further, the computer means is configured to: calculating the amplitude ratio between the two channel data to obtain the error of the amplitude-frequency characteristic between the channels; and calculating the angle difference between the two channel data to obtain the error of the inter-channel phase-frequency characteristic.
Further, the FPGA is further configured to: and in the frequency domain, multiplying each frequency point data of each channel by the corresponding correction coefficient respectively to obtain the compensated frequency point data.
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the invention, by measuring the difference of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel of the mixer, the FPGA compensates the amplitude-frequency characteristic and the phase-frequency characteristic of each frequency point, so that the inconsistent error of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel is reduced, the measurement accuracy of the receiver is improved, correct left-right-handed measurement results are obtained for subsequent correct operations such as digital polarization synthesis, and the accuracy of polarization synthesis is ensured;
(2) the invention carries out frequency conversion on the solar radio signals received by the receiver through different channels, carries out FFT operation on the signals by utilizing the FPGA, and multiplies the frequency point data of each channel by a correction coefficient in a frequency domain, thereby reducing or eliminating the error of inconsistency among the channels and obtaining a satisfactory result.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a statistical plot of a portion of a low band observation station;
FIG. 2 is a block diagram of a parabolic antenna signal flow;
FIG. 3 is a block diagram of a data compensation system structure of multi-channel frequency conversion of a solar radio observation system based on FPGA;
FIG. 4 is a schematic diagram of a supplementary parameter measurement method in a multi-channel frequency conversion data compensation method of a solar radio observation system based on an FPGA;
FIG. 5(a) is a graph of amplitude-frequency characteristics;
FIG. 5(b) is a phase-frequency characteristic diagram;
FIG. 6 is a schematic block diagram of complex frequency domain compensation;
FIG. 7 is a schematic diagram of a polarization synthesizer;
FIG. 8 is a schematic diagram of complex summation operations;
FIG. 9 is a schematic diagram of same phase complex addition;
FIG. 10 is a schematic of the same phase complex subtraction;
FIG. 11 is a graph comparing amplitude-frequency characteristics before and after compensation;
fig. 12 is a graph of AB channel phase difference before and after compensation.
Detailed Description
The invention is further described with reference to the following figures and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As shown in FIG. 2, for the horizontal antenna signal H (150-500MHz), the frequency converter converts 150-325MHz to H1(787.5-962.5MHz) and converts the 325-500MHz band to H2(787.5-962.5 MHz); likewise, the vertical antenna signal V is also converted into V1 and V2 by the frequency converter. The actual measurement shows that there is a large difference between the channels, and the amplitude-frequency characteristic is shown in fig. 5(a), and the phase-frequency characteristic is shown in fig. 5 (b). And inputting the same signals into the two paths, wherein the amplitude-frequency characteristic is the amplitude ratio of the two paths of signals, and the phase-frequency characteristic is the phase difference of the two paths. Therefore, the maximum value of the difference of the amplitude-frequency characteristics among the 2 channels exceeds 5dB, and the difference between the maximum value and the minimum value of the whole frequency band can be 6 dB; the phase difference is about 50 degrees at most, and the phase fluctuation of the whole frequency band is large.
And then, polarization synthesis is carried out on the signals, the low-frequency-band antenna array needs to carry out beam synthesis operation on each path of signals, and the difference error of the amplitude-frequency characteristic and the phase-frequency characteristic of each channel signal seriously influences the operation. If the receiver samples the analog polarization synthesizer, the channel-to-channel differences can also affect left and right rotation data changes, creating errors. By adopting an analog circuit design method, components with good consistency are mainly selected, and circuits are redesigned and optimized, the existing frequency conversion circuit is wasted, the redesigned circuit also has the problem, errors can be reduced, inconsistent errors still exist, and errors of frequency points in a frequency band cannot be eliminated.
How to perform compensation operation to overcome errors is obviously unable to meet the requirement of real-time processing if computer software is adopted to process subsequent data, and the data volume is huge. The system adopts a speed of 500Msps, such as the above 4-channel ADC, each sampling point has 14 bits, and the data volume is about 4GB/S and huge, and a general computer has no real-time processing method.
The bandwidth of an observation frequency band of the solar radio digital receiver is generally wide, the sampling bandwidth of an ADC is relatively narrow, the solar radio signals are sent to the ADC in a segmented mode through frequency conversion and converted into digital quantity for processing, and due to the fact that a multi-channel frequency conversion circuit is inconsistent, errors of amplitude-frequency characteristics and phase-frequency characteristics among channels are caused, and the measurement result of the receiver is affected.
Therefore, the application provides a multi-channel frequency conversion data compensation system and method of a solar radio observation system based on an FPGA, and the FPGA is adopted to compensate the solar radio signal inconsistency errors of all channels in real time.
Example 1:
in an exemplary embodiment of the present application, as shown in fig. 3, a multichannel frequency conversion data compensation system for a solar radio observation system based on an FPGA is provided, and the system includes a frequency conversion card, an ADC converter, a computer and an FPGA.
The ADC converter is connected with the variable frequency card and is configured to: and receiving data of each channel of the frequency conversion card, converting the data into digital data, and uploading the digital data to the FPGA.
The FPGA configured to: respectively carrying out FFT operation on the digital data of each channel to obtain frequency domain data of each channel, and uploading the frequency domain data to a computer; and receiving the correction coefficient sent by the computer, and correcting the frequency point data of each channel.
And the computer is configured to measure the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between the channels of the frequency conversion card, calculate the correction coefficient of each frequency point and send the correction coefficient to the FPGA.
In this embodiment, the multichannel frequency conversion data compensation system for the solar radio observation system based on the FPGA further includes a power divider, and the sinusoidal signal source is divided into two equal-amplitude in-phase signals through the power divider and respectively input into two channels of the frequency conversion card; performing analog-to-digital conversion on the two paths of constant-amplitude in-phase signals through two channels of the ADC, and uploading the converted time domain signals to the FPGA; the FPGA carries out FFT operation on the received time domain signals and transforms the time domain signals of the two channels to frequency domain signals.
Specifically, the computer is configured to: calculating the amplitude ratio between the two channel data to obtain the error of the amplitude-frequency characteristic between the channels; and calculating the angle difference between the two channel data to obtain the error of the inter-channel phase-frequency characteristic.
Further, the FPGA is further configured to: and in the frequency domain, multiplying each frequency point data of each channel by the corresponding correction coefficient respectively to obtain the compensated frequency point data.
The ADC converter and the FPGA are integrated on the high-speed data acquisition card, in the acquisition card, different channel signals of the same frequency band are acquired by using an AD, so that the time synchronization of input end signals is ensured, the ADC does not generate phase errors any more, and in the subsequent operation, each frame of data for compensation and polarization is ensured to be input by different channels at the same time, which is particularly important in ensuring the synchronization and the accuracy of compensation.
Example 2:
in another exemplary embodiment of the present application, as shown in fig. 4, a method for compensating data of a solar radio observation system by multi-channel frequency conversion is provided, the method comprising the following steps:
step 1: the ADC converter receives data of each channel of the frequency conversion card and converts the data into digital data.
Step 2: and the FPGA carries out FFT operation on the digital data of each channel respectively to obtain frequency domain data of each channel.
And performing FFT operation on the FPGA in the board card, and converting the time domain signal into a frequency domain signal.
And step 3: measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between channels of the frequency conversion card; and calculating the correction coefficient of each frequency point.
The method for measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between the channels of the frequency conversion card comprises the following steps:
a sinusoidal signal source becomes two paths of completely same signals through a power divider, the two paths are respectively input into 2 channels of a frequency conversion card, analog-to-digital conversion is carried out by utilizing the two channels of the same AD, the time domain data of the AD conversion is directly uploaded to an FPGA (field programmable gate array), the FPGA inside a board card carries out FFT (fast Fourier transform) operation, the time domain signals are converted into a frequency domain, and the data of each channel after the conversion is finished adopt a plurality of R + IjThe mode shows that the complex frequency domain mode, the phase angle and the complex number are:
the amplitude ratio between the data of the two channels reflects the difference of the amplitude and the frequency between the channels, and when the amplitude ratio is 1, the amplitude and the frequency characteristics of the two channels are consistent; the angle difference between the two channel data is the phase deviation between the channels, and when the angle difference is 0, no phase error exists between the two channels.
The invention obtains the error of the amplitude-frequency characteristic between the channels by calculating the amplitude ratio between the data of the two channels; and calculating the angle difference between the two channel data to obtain the error of the inter-channel phase-frequency characteristic.
Specifically, assume that a-channel complex frequency domain signal SAWith a phase angle of
Amplitude of rA(ii) a B-channel complex frequency domain signal SBWith a phase angle of
Amplitude of rB. Then the a-channel and B-channel complex frequency domain signals can be represented as:
correction coefficient delta S of frequency point obtained by dividing channel B by channel ABAComprises the following steps:
and 4, step 4: and the FPGA corrects the frequency point data of each channel by using the correction coefficient.
Specifically, the corrected S is compensatedBComprises the following steps:
SB＝SA*(RΔ+IΔj) (8)
by the equation (8), it can be found that a is compensated into B by multiplying a by a complex number, after compensation, the amplitude ratio of the complex numbers of the two channels is theoretically 1, and the phase difference between B and a is 0. So far, the amplitude-frequency and phase-frequency characteristic errors introduced by the hardware signal transmission channel of the frequency conversion card are compensated, and the implementation logic block diagram is shown in fig. 6.
The invention provides a data compensation method for multi-channel frequency conversion of a solar radio observation system, which comprises the steps of transferring digital signals obtained by high-speed AD sampling to a baseband through digital down-conversion, and then inputting the digital signals into a fast Fourier transform module to carry out 32K-point FFT operation; and obtaining two paths of complex frequency domain data, respectively multiplying the two paths of complex frequency domain data by compensation parameters, and performing polarization synthesis after the two paths of signals are compensated to be consistent, so that the accuracy of the polarization synthesis is ensured, the compensation precision depends on the precision of the correction parameters, the higher the precision of the correction parameters is, the higher the consistency degree of the two input signal channels is after compensation is, and the better the accuracy of the polarization synthesis operation is.
Example 3:
the following lists a performance test example of the multi-channel frequency conversion data compensation method for the solar radio observation system provided by the invention.
After the AD conversion in the acquisition board card, the acquisition board card is transformed into frequency domain data after FFT operation, and then each frequency point needs to be circularly polarized synthetic operation, and the principle of polarized synthetic is shown in fig. 7. The circularly polarized wave can be generated by synthesizing two orthogonal components with a phase difference of 90 degrees, and the circularly polarized signal can be a left-handed signal or a right-handed signal according to the rotation direction of the vector endpoint. The complex number of the A channel is added with the complex number of the B channel to multiply by 90, and the left polarization output is obtained; similarly, the complex number of the B channel plus the complex number of the a channel multiplied by 90 is the right polarization output. And finally, outputting the mode of the left and right circularly polarized complex numbers to a computer. If the A, B channel passes through the frequency conversion card to generate the variation of amplitude-frequency characteristic and phase-frequency characteristic, so that the two channels AB are inconsistent, the result of polarization synthesis is affected, and a large error is generated.
In order to verify the correctness of the data compensation of the multi-channel frequency conversion of the solar radio observation system, the same 0dBm signal is input into the two channels according to the graph of fig. 4, the coefficients of the subsequent polarization synthesis are adjusted, and the complex numbers of the 2 channels are respectively added and subtracted. AB two complex addition operations, which are:
shown in the complex frequency domain as shown in figure 8.
A and B represent the relationship of the signal intensity and angle of two channels before adding compensation coefficient in complex frequency domain, AB is the signal of two channels before compensating and adding directly, it can be seen that before compensating, two input signals can only follow the vector addition method because of the relationship of phase difference, the mode of the sum is smaller than the sum of two channels of signal modes, and can not complete the direct addition and subtraction operation of signal intensity, therefore, the phase difference of the frequency conversion card greatly affects the correctness of the polarization synthesis operation result. When the compensation parameter is added, the compensated signal a becomes a signal with the same amplitude and phase as B, and at this time, the amplitude of the addition synthesized signal is twice that of the single channel, as shown in fig. 9; the amplitude relationship of the subtracted composite signal should be zero as shown in fig. 10.
The calculation process is respectively obtained by the following formula:
according to the above, in the case where two channels input signals of 0dBm identical and compensate the signals to the same amplitude, the degree of accuracy of the compensation can be evaluated by observing the change in the amplitude of the signals after the addition and subtraction synthesis. The frequency points of the intensity comparison experiment result for compensating the difference between the signals of the two channels before and after the compensation are shown in table 1. It can be seen that only the accessory of 310MHz at the joint of two frequency bands of the frequency conversion card attenuates by 11dBm after compensation, other frequency points all attenuate by more than 20dBm, 160MHz itself is very small, and then the attenuation is reduced by about 10dBm, which shows that the inconsistent error of the two channels caused by the frequency conversion card after compensation is obviously reduced.
TABLE 1 two-way Signal Difference intensity comparison
The amplitude-frequency characteristics before and after the whole frequency band compensation processing are shown in fig. 11, and the signal intensity of 0dbm input A, B of each frequency point measured before the compensation and the signal intensity measured after the A channel compensation are displayed; it can be seen that the intensity difference between the channel A and the channel B before compensation is large, and the channel A and the channel B can be approximately equal after compensation. The A, B channel power ratio changes before and after compensation, and the intensity ratio fluctuates around 1 after compensation, so that the consistent intensity can be basically achieved, and the problem is also explained.
The phase angle change before and after compensation is shown in fig. 12, which is the synthetic intensity measured after the reverse synthetic principle is utilized to calculate the phase deviation of two paths of signals after phase compensation. Theoretically, under the condition of consistent signal intensity, the signal intensity obtained by the reverse synthesis after the channel a and the channel B are compensated to be in the same phase should be very weak. In the angle change shown in the figure, in the case of inputting the equidirectional signal, the phase angle difference between the channel a and the channel B before compensation is the upper curve, and the maximum angle difference can reach 70 degrees; the phase difference between the channel A and the channel B after compensation is a lower curve, and it can be seen that the phase difference is less than 12 degrees, and the phase compensation effect is obvious.
Because the errors of the amplitude-frequency characteristic and the phase-frequency characteristic exist among the channels of the frequency conversion circuit, the observation result of the receiver on the solar radio signal is influenced, the invention respectively carries out FFT operation on the data of each channel to obtain the frequency domain signal of each channel, and utilizes FPGA to carry out real-time correction on the numerical value of each frequency point of each channel, namely, multiplying a complex parameter, thereby reducing the errors of the amplitude-frequency characteristic and the phase-frequency characteristic among the channels, obtaining satisfactory results from experimental data, and obtaining the correct left-right rotation measurement result for the subsequent correct operations such as digital polarization synthesis and the like.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (7)
1. A multi-channel frequency conversion data compensation method for a solar radio observation system is characterized by comprising the following steps:
receiving data of each channel of the frequency conversion card and converting the data into digital data;
respectively carrying out FFT operation on the digital data of each channel to obtain frequency domain data of each channel;
measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between channels of the frequency conversion card, and calculating the correction coefficient of each frequency point;
correcting the frequency point data of each channel by using the correction coefficient;
the method for measuring the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between the channels of the frequency conversion card comprises the following steps:
the sinusoidal signal source is divided into two paths of constant-amplitude in-phase signals through the power divider, and the two paths of the constant-amplitude in-phase signals are respectively input into two channels of the frequency conversion card;
performing analog-to-digital conversion on the two paths of constant-amplitude in-phase signals through two channels of the ADC to obtain time domain signals;
performing FFT operation on the time domain signals, converting the time domain signals of the two channels into frequency domain signals, and calculating the amplitude ratio between the data of the two channels to obtain the error of the amplitude-frequency characteristic between the channels; and calculating the angle difference between the two channel data to obtain the error of the inter-channel phase-frequency characteristic.
2. The method for compensating the data of the multi-channel frequency conversion of the solar-radio observation system according to claim 1, wherein the method for calculating the correction coefficient comprises the following steps:
and solving cosine values and sine values corresponding to angles between the frequency point data of the two channels, and multiplying the cosine values and the sine values by the amplitude ratio between the frequency point data of the two channels to respectively obtain real parts and imaginary parts of the correction coefficients.
3. The multi-channel frequency conversion data compensation method for the solar radio observation system according to claim 1, wherein the method for correcting the frequency point data of each channel comprises the following steps:
and in the frequency domain, multiplying each frequency point data of each channel by the corresponding correction coefficient respectively to obtain the compensated frequency point data.
4. A system for realizing the multi-channel frequency conversion data compensation method of the solar radio observation system in claim 1 is characterized by comprising a frequency conversion card, an ADC converter, a computer and an FPGA;
the ADC converter is connected with the variable frequency card and is configured to: receiving data of each channel of the frequency conversion card, converting the data into digital data, and uploading the digital data to the FPGA;
the FPGA configured to: respectively carrying out FFT operation on the digital data of each channel to obtain frequency domain data of each channel, and uploading the frequency domain data to a computer; receiving a correction coefficient sent by a computer, and correcting the frequency point data of each channel;
and the computer is configured to measure the errors of the amplitude-frequency characteristic and the phase-frequency characteristic between the channels of the frequency conversion card, calculate the correction coefficient of each frequency point and send the correction coefficient to the FPGA.
5. The system of claim 4, further comprising a power divider, wherein the sinusoidal signal source is divided into two equal-amplitude in-phase signals by the power divider, and the two equal-amplitude in-phase signals are respectively input to two channels of the frequency conversion card; performing analog-to-digital conversion on the two paths of constant-amplitude in-phase signals through two channels of the ADC, and uploading the converted time domain signals to the FPGA; the FPGA carries out FFT operation on the time domain signals and transforms the time domain signals of the two channels to frequency domain signals.
6. The system of claim 4, wherein the computer utility is configured to: calculating the amplitude ratio between the two channel data to obtain the error of the amplitude-frequency characteristic between the channels; and calculating the angle difference between the two channel data to obtain the error of the inter-channel phase-frequency characteristic.
7. The system of claim 4, wherein the FPGA is further configured to: and in the frequency domain, multiplying each frequency point data of each channel by the corresponding correction coefficient respectively to obtain the compensated frequency point data.
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