CN112130011A - Satellite-borne power amplifier EVM testing method - Google Patents
Satellite-borne power amplifier EVM testing method Download PDFInfo
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Abstract
The invention discloses a method for testing an EVM (error vector magnitude) of a satellite-borne power amplifier, which belongs to the technical field of amplifiers in high-throughput satellites.
Description
Technical Field
The invention belongs to the technical field of amplifiers in high-throughput satellites, and particularly relates to an EVM (error vector magnitude) testing method for a satellite-borne power amplifier.
Background
The test of the Vector Magnitude Error (EVM) in the existing satellite is only carried out on a communication system comprising a baseband and an amplifier, the EVM test of a satellite-borne amplifier is not separately carried out, and the nonlinear indexes for measuring the amplifier are mainly third-order intermodulation and the like; but for high-throughput satellites: with the adoption of higher frequency, higher system bandwidth and higher-order modulation mode for satellite load, the amplifier test index of the traditional space section load cannot accurately represent the degree of the nonlinear characteristic of the amplifier to the system performance deterioration, and the result is that the traditional nonlinear index of the amplifier meets the requirement but the EVM does not meet the index requirement in the actual system test.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method overcomes the defects of the prior art, can accurately measure the EVM of the satellite-borne power amplifier, and efficiently ensures the system communication quality of the high-throughput satellite.
The purpose of the invention is realized by the following technical scheme: a method for testing an EVM of a satellite-borne power amplifier, the method comprising the steps of: the method comprises the following steps: using MATLAB to encode to obtain a standard signal required by a test, and performing standard system encoding on the standard signal to obtain a baseband code; step two: the baseband signal generator carries out frequency spectrum shifting on the baseband code in the step one to obtain a variable frequency modulation signal; step three: carrying out homologous processing on the vector network analyzer and the baseband signal generator in the second step to enable the frequency conversion modulation signal to be synchronous; calibrating an input port and an output port of a vector network analyzer which is not connected to the satellite-borne power amplifier; step four: connecting the input end of the satellite-borne power amplifier with the input port of a vector network analyzer, adding an attenuator into the output end of the satellite-borne power amplifier, then accessing a preset power meter, loading the variable-frequency modulation signal in the step two to the vector network analyzer, obtaining the saturated output power of the satellite-borne power amplifier according to the power reading of the preset power meter, and recording the power of the variable-frequency modulation signal loaded by the vector network analyzer when the saturated output power of the satellite-borne power amplifier is respectively reduced by 0.5dB, 1dB, 2dB and 3 dB; step five: the input end of the tested satellite-borne power amplifier is connected to the input port of the vector network analyzer, and the output end of the tested satellite-borne power amplifier is connected to the output port of the vector network analyzer after being added into the attenuator; the frequency conversion modulation signal in the step two and the vector network in the step four are combinedThe power of a frequency conversion modulation signal loaded by an analyzer is input to a vector network analyzer, the vector network analyzer tests a satellite-borne power amplifier according to the power of the frequency conversion modulation signal, a measurement receiver in the vector network analyzer receives a time domain response of the satellite-borne power amplifier and carries out frequency domain transformation to obtain a discrete value X (k) obtained after Fourier transformation, and a linear operation result X (k) is obtained according to the discrete value X (k) obtained after Fourier transformation and the frequency conversion modulation signal received by a reference receiver in the vector network analyzerLAnd a result of the nonlinear operation X (k)NLFrom the linear result X (k)LAnd a result of the nonlinear operation X (k)NLAnd obtaining the EVM value of the satellite-borne power amplifier.
In the above method for testing the EVM of the satellite borne power amplifier, the following steps are also included between the third step and the fourth step: and if the EVM value is 0.3%, the input port and the output port of the vector network analyzer are calibrated correctly.
In the above method for testing the EVM of the satellite borne power amplifier, in the third step, the calibration processing of the input port and the output port of the vector network analyzer that is not accessed to the satellite borne power amplifier includes the following steps: the input port of the vector network analyzer is connected to a pre-calibrated power meter, a source calibration factor SCF is obtained according to the reading of the power meter, and the power of the vector network analyzer is compensated according to the source calibration factor SCF; and B, respectively accessing an input port and an output port of the vector network analyzer to an electronic calibration piece, loading the variable-frequency modulation signal in the step B to the vector network analyzer, and calibrating the output port of the vector network analyzer according to the variable-frequency modulation signal in the step B and the electronic calibration piece.
In the above test method for the EVM, the expression of the source calibration factor SCF is as follows:
wherein, PMeasFor the power measured for the power meter,
in order to set the power value,Load＝0the load is 0.
In the above method for testing the EVM of the satellite borne power amplifier, in step five, the discrete value x (k) obtained after fourier transform is:
wherein, X (N) is time domain response, k is integer, N is integer, and N is the number of Fourier transform.
In the EVM testing method of the satellite-borne power amplifier, in the fifth step, the linear operation result X (k)LComprises the following steps:
X(k)L＝α*XL
wherein alpha is a linear operation factor, XLIs the overlapping part of the frequency spectrum after receiving the signal in the vector network analyzer and the ideal frequency domain.
In the EVM testing method for the satellite-borne power amplifier, in the fifth step, a nonlinear operation result X (k)NLComprises the following steps:
wherein m is a nonlinear series expansion; f. of(m)Representing a non-linear operation, XNLIs the non-overlapping part of the frequency spectrum after receiving the signal in the vector network analyzer and the ideal frequency domain.
In the above method for testing the EVM of the satellite borne power amplifier, in step five, the EVM value of the satellite borne power amplifier is:
wherein, X (k)LAs a result of linear operation, X (k)NLAs a result of the non-linear operation,
for the resulting tested EVM, PA represents the power amplifier, Δ represents the difference, s is an integer, M is the number of linear operations summed, and N' is the total number of summations.
In the above test method for the EVM of the satellite borne power amplifier, the calibration process for the output port of the vector network analyzer according to the frequency conversion modulation signal and the electronic calibration member in the step two includes the following steps:
firstly, connecting an electronic calibration piece with a vector network analyzer, and waiting for the completion of self-inspection of the electronic calibration piece, wherein the indicator light of the electronic calibration piece is changed from red to green; and then introducing the frequency conversion modulation signal in the step two into a vector network analyzer, opening a power port of the vector network analyzer, setting the power to be 0dBm, clicking for calibration, calibrating a receiver of the vector network analyzer by an electronic calibration piece according to the input frequency conversion modulation signal, and completing calibration of a preset S parameter through open circuit/short circuit/load.
Compared with the prior art, the invention has the following beneficial effects:
the vector network analyzer and the baseband signal generator are used for testing the vector amplitude error, the EVM of the satellite-borne amplifier can be accurately measured, and the system communication quality of the high-throughput satellite is effectively guaranteed.
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Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
fig. 1 is a schematic diagram of an EVM test system of a satellite-borne power amplifier provided by an embodiment of the invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Fig. 1 is a schematic diagram of an EVM test system of a satellite-borne power amplifier provided by an embodiment of the invention. With reference to fig. 1, the present embodiment provides a method for testing an EVM of a satellite-borne power amplifier, where the method includes the following steps:
the method comprises the following steps: using MATLAB to encode to obtain a standard signal required by a test, and performing standard system encoding on the standard signal to obtain a baseband code;
step two: the baseband signal generator carries out frequency spectrum shifting on the baseband code in the step one to obtain a variable frequency modulation signal;
step three: carrying out homologous processing on the vector network analyzer and the baseband signal generator in the second step to enable the frequency conversion modulation signal to be synchronous; calibrating an input port and an output port of a vector network analyzer which is not connected to the satellite-borne power amplifier;
step four: the input end of a preset ideal cable is connected to the input port of the vector network analyzer, the output end of the preset ideal cable is connected to the output port of the vector network analyzer, an EVM value after direct connection is obtained, and if the EVM value is 0.3%, the input port and the output port of the vector network analyzer are correctly calibrated;
step five: connecting the input end of the satellite-borne power amplifier with the input port of a vector network analyzer, adding an attenuator into the output end of the satellite-borne power amplifier, then accessing a preset power meter, loading the variable-frequency modulation signal in the step two to the vector network analyzer, obtaining the saturated output power of the satellite-borne power amplifier according to the power reading of the preset power meter, and recording the power of the variable-frequency modulation signal loaded by the vector network analyzer when the saturated output power of the satellite-borne power amplifier is respectively reduced by 0.5dB, 1dB, 2dB and 3 dB;
step six: the input end of the tested satellite-borne power amplifier is connected to the input port of the vector network analyzer, and the output end of the tested satellite-borne power amplifier is connected to the output port of the vector network analyzer after being added into the attenuator; inputting the frequency conversion modulation signal in the step two and the power loaded with the frequency conversion modulation signal by the vector network analyzer in the step five into the vector network analyzer, testing the satellite-borne power amplifier by the vector network analyzer according to the power loaded with the frequency conversion modulation signal, obtaining a discrete value X (k) obtained after Fourier transform by a measuring receiver in the vector network analyzer after receiving the time domain response of the satellite-borne power amplifier and carrying out frequency domain transform, and obtaining a linear operation result X (k) according to the discrete value X (k) obtained after Fourier transform and the frequency conversion modulation signal received by a reference receiver in the vector network analyzerLAnd a result of the nonlinear operation X (k)NLFrom the linear result X (k)LAnd a result of the nonlinear operation X (k)NLAnd obtaining the EVM value of the satellite-borne power amplifier.
In step one, the tested data is encoded in an actual modulation mode through an MATLAB or a digital platform, and the signal format adopted in the test scheme is as follows: single carrier frequency division multiple access (DFT-S-OFDM) encodes a signal according to a frame structure length, the number of sub-frames, a sub-carrier spacing, and a modulation scheme. The method comprises the steps of utilizing MATLAB to carry out coding, obtaining a standard signal required by the test, wherein the signal format is the MATLAB own m file, not only limiting the modulation mode in the test scheme, but also carrying out standard system coding according to the signal format actually used by the satellite.
In the second step, the standard signals completed in the first step are imported and processed by a baseband signal generator, the m files are imported, the up-conversion processing is carried out according to the number of carriers used by the actual satellite in the test, a vector signal generator of Germany technology is adopted, the baseband signals are subjected to spectrum shifting by a vector signal source, the modulation process of the baseband signals is completed, and the frequency conversion modulation signals generated in the second step are used as input signals of the tested piece.
In the third step, before the vector network analyzer is used to test the amplifier, the vector network analyzer and the vector signal generator appearing in the previous step need to be subjected to homologous processing, so as to ensure that the frequency conversion modulation signal can be accurately synchronized, and simultaneously, a port and two ports of the vector network analyzer which are not connected to the tested piece are subjected to calibration processing, and the calibration is performed according to the following steps:
after the power meter is subjected to zero calibration and calibration, the power meter is used as an accurate calibration source to calibrate the power of the vector network analyzer from-20 dBm to 0dBm, when the calibration is carried out, an input port of the vector network analyzer needs to be connected into a calibrated power probe, the source power calibration process is to carry out point-by-point measurement and correction on source power, offset values of each power meter and the offset value are recorded, and the offset values are recorded as a Source Calibration Factor (SCF) formula and characterized as follows, wherein P isMeasFor the results of the power head test, aVsFor the power setting, the definition of the state with the load of 0 is as follows:
in the calibration process, the whole error item is compensated according to the power of the SCF in the test result;
and (3) calibrating a receiver of the vector network analyzer by utilizing ECAL (electronic calibration), connecting an input port and an output port of the vector network analyzer to an electronic calibration piece respectively, opening the variable frequency modulation signal generated in the step two, calibrating the receiver of the vector network analyzer in a two-port calibration mode according to the indication of the vector network analyzer, and calibrating the S parameter through open circuit/short circuit/load.
Specifically, the calibration processing of the output port of the vector network analyzer according to the frequency conversion modulation signal and the electronic calibration component in the step two includes the following steps: firstly, inserting a USB port of an electronic calibration piece into a USB port of a vector network analyzer, waiting for the electronic calibration piece to finish self-checking, and then changing an indicator light of the electronic calibration piece from red to green; and then, introducing the frequency conversion modulation signal in the step two into the vector network analyzer through an external network cable, opening a power port of the vector network analyzer, setting the power to be 0dBm, clicking calibration (measure option), calibrating a receiver of the vector network analyzer by the electronic calibration piece according to the input frequency conversion modulation signal through a two-port calibration mode, completing calibration of the existing S parameter through open circuit/short circuit/load, completing prompt (finish option) of the vector network analyzer after completion, and storing the file after calibration.
And (3) carrying out error elimination on errors of the vector network analyzer caused by modulation and up-conversion signals of the testing equipment through calibration.
In the fourth step, after the calibration work in the third step is completed, a section of high-frequency-band amplitude-stable phase cable is used for verifying the calibrated test system, the system is called a direct connection system, the input end of the tested ideal cable is connected to one port of the vector network analyzer, the output end of the tested ideal cable is connected to two ports of the vector network analyzer, the EVM test result after direct connection is obtained, the EVM value at the moment is about 0.3%, the step shows that errors brought by the outside can be considered to be completely eliminated, and the measured EVM value is the final test value.
In the fifth step, after the test scheme verification in the fourth step is completed, the test point of the satellite borne power amplifier is firstly tested, one port of the tested piece is connected to one port of the vector network analyzer, the output port of the tested piece is connected to the attenuator and then connected to the power meter, after the power meter is powered on, the vector network analyzer loads the variable frequency modulation signal, and the input variable frequency modulation signal power of the vector network analyzer is recorded when the output power of the satellite borne amplifier is saturated according to the power reading of the power meter and the back is 0.5dB, 1dB, 2dB and 3 dB.
In the sixth step, after the recording of the power of the input variable frequency modulation signal in the sixth step is completed, the tested piece is accessed to a port of the vector network analyzer according to the diagram shown in fig. 1, the input end of the satellite-borne power amplifier is accessed to a port of the vector network analyzer, and the output end of the satellite-borne power amplifier is accessed to a second port of the vector network analyzer after an attenuator is added;
the EVM obtained by definition is given by the following formula, where RMS is the root mean square of the EVM after multiple tests, I (I, j, k) and Q (I, j, k) respectively represent the received signal after passing through the system under test, I (I, j, k) iso(i, j, k) and Qo(i, j, k) denotes the actually transmitted reference signal, NfFor the number of frames in the EVM test (which must be greater than 20), LpIs the packet length (must be greater than the number of OFDM symbols); p0Is the constellation average power;
in the test, without an actual modulation and demodulation process, starting from a frequency domain, the vector network analyzer inputs the frequency-conversion modulation signal power in the step five (the power values obtained in the step five are respectively input according to different backspacing), the vector network analyzer is internally provided with two receivers which are respectively a reference receiver and a measurement receiver, and a satellite-borne power amplifier carries out frequency domain transformation on time domain response received by the measurement receiver to obtain a discrete value X (k) obtained after Fourier transformation:
performing a spectrum operation according to the above formula, wherein x (k) is a discrete value obtained after performing fourier transform, and x (n) is a data value before the transform; comparing reference reception and measurement reception according to an EVM definition formula, and respectively operating a linear part and a nonlinear part; wherein
EVM test value for satellite-borne Power amplifiers, X (k)LAs a result of linear operation, X (k)NLIs the result of the nonlinear operation; reading directly in a vector network analyzerEVM value after comparison:
wherein, X (k)LAs a result of linear operation, X (k)NLAs a result of the non-linear operation,
for the resulting tested EVM, PA represents the power amplifier, Δ represents the difference, s is an integer, M is the number of linear operations summed, and N' is the total number of summations.
For satellite loads, the wireless quality of signals transmitted through a radio frequency amplifier must meet certain requirements, but the modulation scheme in the traditional transparent forwarding load is mainly BPSK, the signals passing through the amplifier are mostly single carrier waves, and the nonlinear indexes are mainly characterized and tested through indexes such as traditional third-order intermodulation, AM/PM and the like. However, as the baseband modulation mode is continuously towards high-order modulation (from BPSK to 8PSK) and the application of a multi-carrier modulation scheme (orthogonal frequency division multiplexing, OFDM) in a low-orbit mobile internet satellite, the frequency band of the power amplifier is also increased from S/C/X to Ka/Q/V frequency band in order to meet the requirement of high throughput; the traditional non-linear index cannot directly reflect the influence of the power amplifier on the system error rate, so that an EVM test must be separately introduced into the amplifier to determine the EVM deterioration of the power amplifier for the whole spatial section when the power amplifier is close to the saturated output, and the EVM deterioration is used as a design guide index of the satellite-borne power amplifier.
As shown in fig. 1, MATLAB is used to generate codes in an actual system, a baseband signal generator is used to generate a standard signal, and a reference signal of the standard signal is given by a vector network analyzer through a vector signal source; the standard signal is converted to the actual input carrier frequency band of the power amplifier through the vector signal source, and the vector signal source also gives out reference signals through the vector network analyzer, so that the reference signals of the three types of test equipment are ensured to be the same; the input ends of the power amplifier and the tested piece (power amplifier) are connected with the input end of the vector network analyzer, and the output ends of the power amplifier and the tested piece (power amplifier) are connected with the attenuator and then pass through the output end of the vector network analyzer.
The test scheme of the vector network analyzer is used for testing without directly passing through a demodulation scheme, and the core test scheme is to obtain a linear part and a distortion part in an amplifier transmission function by performing relevant operation on an input and output frequency spectrum, so that the EVM of the amplifier is obtained, the test complexity is reduced, and the consistency of the test result is improved.
According to actual test results, for an amplifier working in a Ka frequency band and having a bandwidth of 1G, a multi-carrier scheme (DFT-S-OFDM) and a high-order modulation scheme (8PSK) are used for testing in a calibration state (direct connection) and a tested part backspacing state respectively, and the test results show that the EVM under the direct connection condition is about 0.3%, which is far better than that of a test scheme adopting a frequency spectrograph in a twice frequency conversion scheme.
Spectrum analyzer test scheme and VNA test scheme
| Pin | OBO (output rollback) | Traditional EVM scheme | EVM testing scheme of the invention |
| EVM in direct connection state | / | 4％ | 0.3％ |
Conventional EVM testing is typically performed at the entire system level, including after baseband processing and variable frequency amplification, and the test scenario is typically read directly with a spectrometer. The embodiment adopts a new EVM testing method for the power amplifier, and is suitable for testing the EVM of the microwave amplifier under a high-flux high-order modulation system. The vector network analyzer and the baseband frequency conversion test system are utilized to simplify the test process, the test result can be directly read through the VNA, and the inconsistency caused by different modulation and demodulation schemes is reduced.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (8)
1. A method for testing an EVM (error vector magnitude) of a satellite-borne power amplifier is characterized by comprising the following steps:
the method comprises the following steps: using MATLAB to encode to obtain a standard signal required by a test, and performing standard system encoding on the standard signal to obtain a baseband code;
step two: the baseband signal generator carries out frequency spectrum shifting on the baseband code in the step one to obtain a variable frequency modulation signal;
step three: carrying out homologous processing on the vector network analyzer and the baseband signal generator in the second step to enable the frequency conversion modulation signal to be synchronous; calibrating an input port and an output port of a vector network analyzer which is not connected to the satellite-borne power amplifier;
step four: connecting the input end of the satellite-borne power amplifier with the input port of a vector network analyzer, adding an attenuator into the output end of the satellite-borne power amplifier, then accessing a preset power meter, loading the variable-frequency modulation signal in the step two to the vector network analyzer, obtaining the saturated output power of the satellite-borne power amplifier according to the power reading of the preset power meter, and recording the power of the variable-frequency modulation signal loaded by the vector network analyzer when the saturated output power of the satellite-borne power amplifier is respectively reduced by 0.5dB, 1dB, 2dB and 3 dB;
step five: the input end of the tested satellite-borne power amplifier is connected to the input port of the vector network analyzer, and the output end of the tested satellite-borne power amplifier is connected to the output port of the vector network analyzer after being added into the attenuator; inputting the frequency conversion modulation signal in the step two and the power loaded with the frequency conversion modulation signal by the vector network analyzer in the step four into the vector network analyzer, testing the satellite-borne power amplifier by the vector network analyzer according to the power loaded with the frequency conversion modulation signal, obtaining a discrete value X (k) obtained after Fourier transform by a measuring receiver in the vector network analyzer after receiving the time domain response of the satellite-borne power amplifier and carrying out frequency domain transform, and obtaining a linear operation result X (k) according to the discrete value X (k) obtained after Fourier transform and the frequency conversion modulation signal received by a reference receiver in the vector network analyzerLAnd a result of the nonlinear operation X (k)NLFrom the linear result X (k)LAnd a result of the nonlinear operation X (k)NLAnd obtaining the EVM value of the satellite-borne power amplifier.
2. The EVM test method for a satellite-borne power amplifier according to claim 1, characterized in that: the method also comprises the following steps between the third step and the fourth step: and if the EVM value is 0.3%, the input port and the output port of the vector network analyzer are calibrated correctly.
3. The EVM test method for a satellite-borne power amplifier according to claim 1, characterized in that: in step three, the calibration processing of the input port and the output port of the vector network analyzer which is not connected to the satellite-borne power amplifier comprises the following steps:
the input port of the vector network analyzer is connected to a pre-calibrated power meter, a source calibration factor SCF is obtained according to the reading of the power meter, and the power of the vector network analyzer is compensated according to the source calibration factor SCF;
and B, respectively accessing an input port and an output port of the vector network analyzer to an electronic calibration piece, loading the variable-frequency modulation signal in the step B to the vector network analyzer, and calibrating the output port of the vector network analyzer according to the variable-frequency modulation signal in the step B and the electronic calibration piece.
4. The EVM testing method of the satellite-borne power amplifier according to claim 3, characterized in that: the expression of the source calibration factor SCF is as follows:
wherein, PMeasPower for power measurement, aVsIn order to set the power value,Load＝0the load is 0.
5. The EVM test method for a satellite-borne power amplifier according to claim 1, characterized in that: in step five, the discrete value x (k) obtained after fourier transform is:
wherein, X (N) is time domain response, k is integer, N is integer, and N is the number of Fourier transform.
6. The EVM test method for a satellite-borne power amplifier according to claim 1, characterized in that: in step five, the result of the linear operation X (k)LComprises the following steps:
X(k)L＝α*XL
wherein alpha is a linear operation factor, XLFor the frequency spectrum and ideal after receiving the signal in the vector network analyzerThe frequency domain overlaps.
7. The EVM testing method of the satellite-borne power amplifier according to claim 6, characterized in that: in step five, the result of the nonlinear operation X (k)NLComprises the following steps:
wherein m is a nonlinear series expansion; f. of(m)Representing a non-linear operation, XNLIs the non-overlapping part of the frequency spectrum after receiving the signal in the vector network analyzer and the ideal frequency domain.
8. The EVM testing method of the satellite-borne power amplifier according to claim 7, characterized in that: in step five, the EVM value of the satellite-borne power amplifier is:
wherein, X (k)LAs a result of linear operation, X (k)NLAs a result of the non-linear operation,
for the resulting tested EVM, PA represents the power amplifier, Δ represents the difference, s is an integer, M is the number of linear operations summed, and N' is the total number of summations.
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| CN112130011B (en) | 2023-12-12 |
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