CN113484549A - EVM measuring method suitable for OTA test - Google Patents

EVM measuring method suitable for OTA test Download PDF

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CN113484549A
CN113484549A CN202110681569.9A CN202110681569A CN113484549A CN 113484549 A CN113484549 A CN 113484549A CN 202110681569 A CN202110681569 A CN 202110681569A CN 113484549 A CN113484549 A CN 113484549A
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evm
vector
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CN113484549B (en
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陈海东
林伟杰
王帅
罗泽文
车文荃
薛泉
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South China University of Technology SCUT
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Abstract

The invention discloses an EVM measuring method suitable for OTA test, which comprises the following steps: the method comprises the following steps of firstly, constructing different error vector magnitude measurement systems, wherein each error vector magnitude measurement system comprises a first measurement system, a second measurement system and a third measurement system; step two, measuring the error vector magnitude under different error vector magnitude measuring systems; step three, obtaining error vector magnitude measurement values of different error vector magnitude measurement systems; and step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained by different measuring systems. The measuring method is suitable for OTA testing conditions, vector modulation errors caused by instrument factors and vector modulation errors caused by environment factors are calculated and obtained by building three testing links, and the two interferences are eliminated by vector difference calculation, so that the vector modulation errors of the device to be tested are more accurate through measurement and calculation.

Description

EVM measuring method suitable for OTA test
Technical Field
The invention relates to the technical field of radio frequency terminal testing in the field of wireless communication, in particular to an EVM measuring method suitable for OTA testing.
Background
Error Vector Magnitude (EVM), which is the Vector difference between an ideal reference signal and a measurement signal at a given time, is an important index for evaluating the signal quality after Vector modulation in a communication system, and can visually reflect the Magnitude Error and the phase Error between the measurement signal and the reference signal. The error vector magnitude can be calculated by comparing the difference between the vector values of the measurement signal and the reference signal, as shown in fig. 1.
The Air interface radiation (OTA) test is to simulate The wireless transmission environment in a microwave darkroom and test The performance of The device to be tested in The simulated wireless transmission environment. The new generation of 5G wireless communication technology includes a 5G active antenna system, the 5G active antenna system integrates an antenna and a radio frequency RRU module, and an output port of the radio frequency RRU module becomes an internal interface of the system, so that the EVM measurement of a device to be measured cannot be performed by a conventional conduction method but by a far-field OTA test method.
For EVM testing of Vector modulated signals, measurements must be made on the transmitter and receiver sections using a Vector Signal Generator (VSG) and a Vector Signal Analyzer (VSA), respectively. Under the conditions of different output power and receiving power, nonlinear components (a mixer and an amplifier) in a vector signal generator and a vector signal analyzer can introduce different equipment measurement errors to the EVM measurement of a device to be measured, so that the EVM measurement of the device to be measured cannot be accurately performed, and particularly in OTA (over the air) test, due to the fact that the insertion loss of a test system is extremely large, the power of a signal received by a VSA (voltage-dependent amplifier) is low, a preamplifier inside the VSA is required to amplify the received signal, the nonlinear influence from the equipment is introduced, and the EVM measurement of the device to be measured is interfered.
In the prior art, error vector amplitude compensation is performed on an EVM test instrument only by a conduction method, and measurement and compensation of error vector amplitude errors caused by the EVM test instrument under an OTA test condition are lacked (publication No. CN 102546036 a, an error vector amplitude compensation method); in addition, only the error vector amplitude error introduced by the vector signal analyzer VSA is considered, but the error vector amplitude error also introduced by the vector signal generator VSG is not considered, so that the measurement result is inaccurate, and an instrument error exists (CN 110518988A, an apparatus and a method for measuring a device vector modulation error).
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide an error vector magnitude measuring method under an OTA test condition, which is used to solve the problem that an EVM measurement result is inaccurate due to instrument factors and environmental factors under the OTA test condition, so as to obtain an accurate EVM value of a device under test through measurement and calculation.
The invention is realized by at least one of the following technical schemes.
An EVM measuring method suitable for OTA test comprises the following steps:
the method comprises the following steps of firstly, constructing different error vector magnitude measurement systems, wherein each error vector magnitude measurement system comprises a first measurement system, a second measurement system and a third measurement system;
step two, measuring the error vector magnitude under different error vector magnitude measuring systems;
step three, obtaining error vector magnitude measurement values of different error vector magnitude measurement systems;
and step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained by different measuring systems.
Preferably, the first measurement system comprises a first vector signal generator VSG, a first vector signal analyzer VSA, a first radio frequency cable No. 1, a first radio frequency cable No. 2, a first test antenna No. 1, and a first test antenna No. 2;
the second measurement system comprises a second vector signal generator VSG, a second vector signal analyzer VSA, a second No. 1 radio frequency cable, a second No. 2 radio frequency cable, a second test antenna and a device to be tested DUT;
the third measurement system comprises a third vector signal generator VSG, a third vector signal analyzer VSA, a third No. 1 radio frequency cable and a third No. 2 radio frequency cable.
Preferably, the performance and the appearance of the first test antenna No. 1, the first test antenna No. 2 and the second test antenna are completely consistent; the first radio frequency cable No. 1, the first radio frequency cable No. 2, the radio frequency cable No. 1, the radio frequency cable No. 2, the radio frequency cable No. 1 and the radio frequency cable No. 2 are isometric cables of the same type, and the performance and the appearance are completely consistent.
Preferably, in the first measurement system, the direct measurement value of the EVM is represented by:
Figure BDA0003122830950000021
wherein EVMOTA,S1Is a direct measure of the EVM under the first measurement system, PTX1Is the magnitude of the power of the VSG transmission signal of the first vector signal generator in dBm, PRX1The power level of the received signal, in dBm,
Figure BDA0003122830950000022
to transmit at a signal power of PTX1Received signal power of PRX1Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,
Figure BDA0003122830950000023
the error vector magnitude introduced for the first test antenna No. 1 under the first measurement system OTA test condition,
Figure BDA0003122830950000024
is the first measurementMeasuring the error vector magnitude introduced by the first test antenna No. 2 under the system OTA test condition;
in the second measurement system, the direct measurement value of the EVM is represented as:
Figure BDA0003122830950000031
Figure BDA0003122830950000032
wherein EVMOTA,S2Is a direct measure of EVM under the second measurement system,
Figure BDA0003122830950000033
for transmitting signal power P at VSG of second vector signal generatorTX2Under the condition, the error vector amplitude introduced by the device to be tested,
Figure BDA0003122830950000034
the error vector magnitude introduced by the second test antenna under the OTA test condition of the second measurement system;
Figure BDA0003122830950000035
representing the magnitude of the error vector introduced by the rf module of the device under test,
Figure BDA0003122830950000036
representing the magnitude of the error vector introduced by the antenna module of the device under test,
Figure BDA0003122830950000037
and
Figure BDA0003122830950000038
error proper amplitude EVM (error vector magnitude) jointly forming instrument to be measuredDUT(PTX2)。
In the third measurement system, the direct measurement value of the EVM is represented as:
Figure BDA0003122830950000039
wherein EVMOTA,S3Is a direct measure of EVM under a third measurement system, PRX3Magnitude of power of signal transmitted for third vector signal generator VSG, PTX3The power of the VSA receiving signal of the third vector signal analyzer is measured by three measuring systems to obtain an EVM direct measurement value EVMOTA,S1、EVMOTA,S2、EVMOTA,S3。
Preferably, the distance L1 measured by the first measurement system is the same size as the distance L2 measured by the second measurement system.
Preferably, the VSG emission signal power of each measurement system vector signal generator is consistent, PTX1＝PTX2＝PTX3(ii) a Keeping VSA receiving signal power of each measuring system consistent, PRX1＝PRX2＝PRX3。
Preferably, the EVM measurement value of the component under test
Figure BDA00031228309500000310
Comprises the following steps:
Figure BDA00031228309500000311
preferably, the first measurement system operates as follows:
setting a first vector signal generator VSG to output a digital modulation signal with output power P1; opening the first vector signal analyzer VSA, and setting analysis signal parameters of the first vector signal analyzer VSA, so that the first vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P2; recording the EVM value obtained by the VSA measurement of the current first vector signal analyzer as EVMOTA,S1。
Preferably, the second test system operates as follows:
setting a second vector signal generator VSG to output a digital modulation signal with the output power of P1; opening the firstThe two vector signal analyzers VSA are used for setting analysis signal parameters of the second vector signal analyzer VSA, so that the second vector signal analyzer VSA can normally demodulate received signals, and the power of the received signals is P3; adjusting the size of an attenuator of the second vector signal analyzer VSA to Gatt1(Gatt1 ≈ P3-P2), so that the power of a signal received by the second vector signal analyzer VSA is equal to P2 after passing through the attenuator; recording the EVM value obtained by the VSA measurement of the current second vector signal analyzer as EVMOTA,S2。
Under the third test system, the digital modulation signal generated by the third vector signal generator VSG directly enters the receiving port of the third vector signal analyzer VSA through the third radio frequency cable No. 1 and the third radio frequency cable No. 2 in a conduction method.
The third test system operates as follows:
setting a third vector signal generator VSG to output a digital modulation signal, and outputting power P1; opening a third vector signal analyzer VSA, and setting analysis signal parameters of the third vector signal analyzer VSA, so that the third vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P4; adjusting the size of an attenuator of the third vector signal analyzer VSA to Gatt2, so that the size of the signal power received by the third vector signal analyzer VSA is equal to P2 after the signal power is subjected to the attenuator Gatt2(Gatt2 ≈ P4-P2); recording the EVM value measured by the VSA of the current third vector signal analyzer as EVMOTA,S3。
And substituting direct EVM measurement values obtained by measurement under the three measurement system conditions into a formula (4) to obtain an EVM measurement value of the device to be measured.
The measuring method is suitable for OTA testing conditions, vector modulation errors caused by instrument factors and vector modulation errors caused by environment factors are calculated and obtained by building three testing links, and the two interferences are eliminated by vector difference calculation, so that the vector modulation errors of the device to be tested are more accurate through measurement and calculation.
Compared with the prior art, the invention has the beneficial effects that:
an EVM measuring method based on OTA test conditions is provided for an integrated instrument to be tested at the front end of an antenna or a multi-channel instrument to be tested. Compared with the EVM measuring method applied under the conduction method condition, the invention is suitable for testing the instruments to be tested of a plurality of receiving and transmitting channels under the OTA measuring condition, improves the EVM testing speed, and the testing condition is closer to the actual working condition of the instruments to be tested.
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FIG. 1 is a schematic diagram illustrating the definition of vector modulation errors involved in the method of the present invention;
FIG. 2 is a schematic view of a first measurement system according to an embodiment of the present invention;
FIG. 3 is a schematic view of a second measurement system according to an embodiment of the present invention;
FIG. 4 is a schematic view of a third measurement system according to an embodiment of the present invention;
FIG. 5 is an EVM measurement flow diagram according to an embodiment of the present invention;
fig. 6 is a structural diagram of a DUT device under test according to embodiment 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail by the following examples.
Example 1:
an EVM measuring method suitable for OTA test comprises the following steps:
step one, an EVM measuring system with different building modes is described; the EVM measuring system comprises a first measuring system, a second measuring system and a third measuring system;
the first measurement system is constructed in a manner shown in fig. 2, and S1 represents that the first measurement system S1 includes a first vector signal generator VSG, a first vector signal analyzer VSA, a first radio frequency cable No. 1, a first radio frequency cable No. 2, a first test antenna No. 1, and a first test antenna No. 2. The first vector signal generator VSG is connected with the first test antenna No. 1 through a first No. 1 radio frequency cable, and a modulation signal generated by the first vector signal generator VSG is transmitted to a free space through the first test antenna No. 1; the first vector signal analyzer VSA is connected with a first test antenna 2 through a first No. 2 radio frequency cable, the horizontal distance between a No. 1 caliber plane of the first test antenna and a No. 2 caliber plane of the first test antenna is L, and the first test antenna 2 transmits a received modulation signal to the VSA for signal demodulation;
the second measurement system is constructed in a manner as shown in fig. 3, and the second measurement system S2 includes a second vector signal generator VSG, a second vector signal analyzer VSA, a second radio frequency cable No. 1, a second radio frequency cable No. 2, a second test antenna, and a device under test DUT. The second vector signal generator VSG is connected with a DUT (device under test) through a second No. 1 radio frequency cable, and a modulation signal generated by the second vector signal generator VSG is transmitted to a free space through the DUT; the second vector signal analyzer VSA is connected with a second test antenna through a second No. 2 radio frequency cable, the horizontal distance between the antenna aperture plane of the DUT and the aperture plane of the second test antenna is L, and the second test antenna transmits the received modulation signal to the VSA for signal demodulation;
the third measurement system is constructed in a manner as shown in fig. 4, and the third measurement system S3 includes a third vector signal generator VSG, a third vector signal analyzer VSA, a third radio frequency cable No. 1, and a third radio frequency cable No. 2. The modulation signal generated by the third vector signal generator VSG passes through the third radio frequency cable No. 1 and the third radio frequency cable No. 2 to reach a receiving port of a third vector signal analyzer VSA, and the third vector signal analyzer VSA demodulates the received signal;
in the measurement systems S1, S2, and S3, the performance and the shape of the first test antenna No. 1, the first test antenna No. 2, and the second test antenna are completely consistent; the first radio frequency cable No. 1, the first radio frequency cable No. 2, the second radio frequency cable No. 1, the second radio frequency cable No. 2, the third radio frequency cable No. 1 and the third radio frequency cable No. 2 are isometric cables of the same type;
step two, establishing the relation between instrument factors, environment factors and EVM;
in the first measurement system, the direct measurement value of the EVM is represented as:
Figure BDA0003122830950000051
wherein EVMOTA,S1Is a direct measurement of EVM under the first measurement system, PTX1Is the magnitude of the power of the VSG transmission signal of the first vector signal generator in dBm, PRX1The power level of the received signal, in dBm,
Figure BDA0003122830950000061
to transmit at a signal power of PTX1Received signal power of PRX1Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,
Figure BDA0003122830950000062
for the error vector magnitude introduced by the first test antenna No. 1 with OTA test distance L,
Figure BDA0003122830950000063
the error vector magnitude introduced by the first test antenna No. 2 under the condition that the OTA test distance is L is because the first test antenna No. 1 and the first test antenna No. 2 are completely the same antenna, so that the test method has the advantages of simple structure, low cost and high test accuracy
Figure BDA0003122830950000064
Size equal to
Figure BDA0003122830950000065
In the second measurement system, the direct measurement value of the EVM is represented as:
Figure BDA0003122830950000066
Figure BDA0003122830950000067
wherein EVMOTA,S2Is a direct measurement of the EVM under the second measurement system,
Figure BDA0003122830950000068
for transmitting signal power P at VSG of second vector signal generatorTX2Under the condition, the error vector magnitude introduced by the device to be tested.
Figure BDA0003122830950000069
Representing the power of the transmitted signal at the second vector signal generator VSG as PTX2Under the condition, the error vector magnitude introduced by the radio frequency module of the device to be tested,
Figure BDA00031228309500000610
the error vector magnitude introduced by the antenna module of the device under test is represented, and the error vector magnitude together form the proper error magnitude of the instrument under test, as expressed by the formula (3).
In the third measurement system, the direct measurement value of the EVM is represented as:
Figure BDA00031228309500000611
wherein EVMOTA,S3Is a direct measure of EVM under the third measurement system.
The EVM direct measurement value EVM is obtained through the measurement of the three measurement systemsOTA,S1、EVMOTA,S2、EVMOTA,S3The VSG transmitting power P in the vector signal generator is obtained through calculation of formula (1) to formula (4)TXUnder the condition, the EVM measured value of the element to be tested
Figure BDA00031228309500000612
Expressed as:
Figure BDA00031228309500000613
step three, error vector magnitude EVM measurement is carried out under different measurement systems;
under the first measurement system, the digital modulation signal generated by the first vector signal generator VSG is converted by the first test antenna No. 1In order to receive the electromagnetic wave propagating in the free space by the first test antenna No. 2 with a distance L, wherein L is the horizontal distance between the No. 1 aperture plane of the first test antenna and the No. 2 aperture plane of the first test antenna, the size of L must reach the far-field condition distance of the No. 2 first test antenna,
Figure BDA00031228309500000614
λ is the wavelength of the electromagnetic wave, and D is the aperture of the first test antenna No. 2. The first measurement system operates as follows:
setting a first vector signal generator VSG to output a digital modulation signal with output power P1; opening the first vector signal analyzer VSA, and setting analysis signal parameters of the first vector signal analyzer VSA, so that the first vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P2; recording the EVM value obtained by the VSA measurement of the current first vector signal analyzer as EVMOTA,S1。
Under an S2 test system, a digital modulation signal generated by a second vector signal generator VSG is converted into an electromagnetic wave propagating in a free space through a device to be tested DUT, and the electromagnetic wave is received by a second measuring antenna No. 2 with a distance L, wherein L is the horizontal distance between the antenna aperture plane of the device to be tested DUT and the second measuring antenna aperture plane; the second vector signal generator VSG decomposes the received signal into I and Q component signals, and the I and Q component signals obtained by decomposition are compared with I in an ideal demodulation state to obtain a required EVM direct measurement value.
The S2 test system operates as follows:
setting a second vector signal generator VSG to output a digital modulation signal with the output power of P1; opening a second vector signal analyzer VSA, and setting analysis signal parameters of the second vector signal analyzer VSA, so that the second vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P3; adjusting the size of an attenuator of the second vector signal analyzer VSA to Gatt1(Gatt1 ≈ P3-P2), so that the power of the signal received by the second vector signal analyzer VSA is approximately equal to P2 after passing through the attenuator; record the current second vector signal analyzer VSThe EVM value obtained by A measurement is EVMOTA,S2。
Under the test system of S3, the digital modulation signal generated by the third vector signal generator VSG directly enters the receiving port of the third vector signal analyzer VSA through the third radio frequency cable No. 1 and the third radio frequency cable No. 2 in a conduction mode.
The S3 test system operates as follows:
setting a third vector signal generator VSG to output a digital modulation signal, and outputting power P1; opening a third vector signal analyzer VSA, and setting analysis signal parameters of the third vector signal analyzer VSA, so that the third vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P4; adjusting the size of an attenuator of the third vector signal analyzer VSA to Gatt2, so that Gatt2 is approximately equal to P4-P2, and the power of a signal received by the third vector signal analyzer VSA is approximately equal to P2 after passing through the attenuator; recording the EVM value measured by the VSA of the current third vector signal analyzer as EVMOTA，S3。
Substituting EVM direct measurement values measured under the conditions of the three measurement systems into a formula (5), and calculating to eliminate vector modulation errors caused by instrument factors and vector modulation errors caused by environmental factors to obtain the vector modulation errors of the device to be measured
Figure BDA0003122830950000071
The measuring mode of the invention eliminates the influence of instrument factors and environmental factors on the EVM measurement of the device to be measured under the OTA condition.
Example 2:
according to the schematic diagrams of the first measurement system (S1), the second measurement system (S2) and the third measurement system (S3) in fig. 2, 3 and 4, the EVM measurement system is built, the system parameters of the vector signal generator and the vector signal analyzer are set, and the specific configuration of the software and hardware conditions of the device is shown in table 1 and table 2:
(1) vector signal generator SMW200A
TABLE 1 SMW200A parameter configuration diagram
Figure BDA0003122830950000081
(2) Vector signal analyzer R & S FSW43
TABLE 2R & S FSW43 parameter configuration diagram
Figure BDA0003122830950000082
(3) The first test antenna 1 and the first test antenna 2 of the three measurement systems are respectively a multi-octave horn antenna LB-180400-KF of the Union microwave;
as shown in fig. 5, the method for operating EVM measurement suitable for OTA testing includes the following steps:
step 101, setting the output power of the vector signal generator, recording the output power P1 of the current vector signal generator, and measuring the power signal P2 and the EVM received by the vector signal analyzer. The results of 5 replicate measurements and mean calculations are shown in table 3.
TABLE 3 Experimental measurements and calculations based on the procedure of step 101
Figure BDA0003122830950000083
Figure BDA0003122830950000091
And 102, setting the output power of the vector signal generator, keeping the output power of the current vector signal generator to be P1, and setting the size of an attenuator Gatt1 according to the size of a power signal P3 received by the vector signal analyzer, so that P3-Gatt2 is approximately equal to P2. The results of 5 replicate measurements and mean calculations are shown in table 4.
TABLE 4 results of experimental measurements and calculations performed according to step 102
Figure BDA0003122830950000092
Step 103, setting the output power of the vector signal generator, keeping the output power of the current vector signal generator at P1, and setting the size of an attenuator Gatt2 according to the size of a power signal P4 received by the vector signal analyzer, so that P4-Gatt2 is approximately equal to P2. The results of 5 replicate measurements and mean calculations are shown in table 5.
TABLE 5 Experimental measurements and calculations based on the procedure of step 103
Figure BDA0003122830950000093
Figure BDA0003122830950000101
For the present embodiment, the EVM is measured through steps 101 to 103OTA，S1＝7.88％,EVMOTA，S2＝9.53％,EVMOTA，S37.20%. Through the calculation of the formula (4), the vector error caused by the device to be tested under the OTA test condition is obtained
Figure BDA0003122830950000102
Example 3:
in order to verify the accuracy of the EVM measurement result of the present invention, the DUT used in embodiment 2 is composed of three parts as shown in fig. 6: the device comprises a DUT radio frequency module, a DUT antenna and a DUT radio frequency cable; the DUT radio frequency cable is connected with the DUT radio frequency module and the DUT antenna, and the DUT radio frequency module and the DUT antenna can be separated by removing the DUT radio frequency cable, wherein the DUT radio frequency module is composed of an LNA power amplifier module, the DUT antenna is a multi-octave horn antenna LB-180400-KF of Union microwave and is consistent with the antenna adopted in embodiment 2, and the DUT radio frequency cable is consistent with the radio frequency cable adopted in embodiment 2.
Since the DUT antenna is identical to that used in example 2, it can be said that
Figure BDA0003122830950000103
Figure BDA0003122830950000104
Calculating through formula (1) to formula (4) to obtain VSG transmitting power P in the vector signal generatorTXUnder the condition, the EVM value of the DUT radio frequency module in the device to be tested
Figure BDA0003122830950000105
Expressed as:
Figure BDA0003122830950000106
the data measured in the embodiment 2 is calculated by the formula (5) to obtain the vector error caused by the DUT radio frequency module of the device to be tested under the OTA test condition
Figure BDA0003122830950000107
EVM measurement is carried out on the DUT radio frequency module by adopting a conduction method, and the measurement result is 5.23 percent
For the DUT radio frequency module, the conduction EVM measurement results and the EVM measurement results of the present invention are compared, and the data pair ratio is shown in table 6:
TABLE 6 comparison of the EVM measurements by the conductive method with those of the present invention
conduction-EVM measurement EVM measurement of the invention Both of themDifference value
EVM(％) 5.23 5.36 0.13
The test result in embodiment 3 shows that, in the OTA test system, three different hardware connection modes are used to obtain the error vector value of the DUT radio frequency module in the instrument to be tested separately, and the difference between the result obtained by the conduction method measurement and the result obtained by the conduction method measurement is 0.13%, which can be considered to be within the experimental error range.
The embodiment adopts an EVM measuring method suitable for the OTA test environment. Through three different hardware connection modes, equipment factors and the influence of environmental factors on the measurement of the EVM of the device to be measured are eliminated, and the error vector magnitude caused by the device to be measured is obtained through calculation. A new EVM measuring method is provided for the device to be measured with the antenna and the radio frequency module integrated.
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 (10)

1. An EVM measuring method suitable for OTA test is characterized by comprising the following steps:
the method comprises the following steps of firstly, constructing different error vector magnitude measurement systems, wherein each error vector magnitude measurement system comprises a first measurement system, a second measurement system and a third measurement system;
step two, measuring the error vector magnitude under different error vector magnitude measuring systems;
step three, obtaining error vector magnitude measurement values of different error vector magnitude measurement systems;
and step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained by different measuring systems.
2. The EVM measuring method suitable for OTA test according to claim 1, wherein the first measuring system comprises a first vector signal generator VSG, a first vector signal analyzer VSA, a first radio frequency cable No. 1, a first radio frequency cable No. 2, a first test antenna No. 1, a first test antenna No. 2;
the second measurement system comprises a second vector signal generator VSG, a second vector signal analyzer VSA, a second No. 1 radio frequency cable, a second No. 2 radio frequency cable, a second test antenna and a device to be tested DUT;
the third measurement system comprises a third vector signal generator VSG, a third vector signal analyzer VSA, a third No. 1 radio frequency cable and a third No. 2 radio frequency cable.
3. The EVM measuring method suitable for OTA test according to claim 2, wherein the first test antenna No. 1, the first test antenna No. 2 and the second test antenna have completely consistent performance and appearance; the first radio frequency cable No. 1, the first radio frequency cable No. 2, the radio frequency cable No. 1, the radio frequency cable No. 2, the radio frequency cable No. 1 and the radio frequency cable No. 2 are isometric cables of the same type, and the performance and the appearance are completely consistent.
4. The EVM measuring method suitable for OTA test according to claim 3, wherein in the first measuring system, the direct measurement value of the EVM is represented as:
Figure FDA0003122830940000011
wherein EVMOTA,S1Is a direct measure of the EVM under the first measurement system, PTX1Is the magnitude of the power of the VSG transmission signal of the first vector signal generator in dBm, PRX1The power level of the received signal, in dBm,
Figure FDA0003122830940000012
to transmit at a signal power of PTX1Received signal power of PRX1Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,
Figure FDA0003122830940000013
the error vector magnitude introduced for the first test antenna No. 1 under the first measurement system OTA test condition,
Figure FDA0003122830940000014
error vector magnitude introduced for the No. 2 first test antenna under the OTA test condition of the first measurement system;
in the second measurement system, the direct measurement value of the EVM is represented as:
Figure FDA0003122830940000021
Figure FDA0003122830940000022
wherein EVMOTA,S2Is a direct measure of EVM under the second measurement system,
Figure FDA0003122830940000023
for transmitting signal power P at VSG of second vector signal generatorTX2Under the condition, the error vector amplitude introduced by the device to be tested,
Figure FDA0003122830940000024
the error vector magnitude introduced by the second test antenna under the OTA test condition of the second measurement system;
Figure FDA0003122830940000025
representing the magnitude of the error vector introduced by the rf module of the device under test,
Figure FDA0003122830940000026
representing the magnitude of the error vector introduced by the antenna module of the device under test,
Figure FDA0003122830940000027
and
Figure FDA0003122830940000028
error proper amplitude EVM (error vector magnitude) jointly forming instrument to be measuredDUT(PTX2)；
In the third measurement system, the direct measurement value of the EVM is represented as:
Figure FDA0003122830940000029
wherein EVMOTA,S3Is a direct measure of EVM under a third measurement system, PRX3Magnitude of power of signal transmitted for third vector signal generator VSG, PTX3The power of the VSA receiving signal of the third vector signal analyzer is measured by three measuring systems to obtain an EVM direct measurement value EVMOTA,S1、EVMOTA,S2、EVMOTA,S3。
5. The EVM measuring method suitable for OTA testing according to claim 4, wherein the distance L1 measured by the first measuring system is the same size as the distance L2 measured by the second measuring system.
6. EVM test applicable to OTA test according to claim 5Method for measuring the power of VSG signals, characterized in that the VSG signal power of each measurement system is identical, PTX1＝PTX2＝PTX3(ii) a Keeping VSA receiving signal power of each measuring system consistent, PRX1＝PRX2＝PRX3。
7. The EVM measuring method suitable for OTA test according to claim 6, wherein the EVM measured value of the element under test
Figure FDA00031228309400000210
Comprises the following steps:
Figure FDA00031228309400000211
8. the EVM measurement method applicable to OTA testing according to claim 7, wherein the first measurement system operates as follows:
setting a first vector signal generator VSG to output a digital modulation signal with output power P1; opening the first vector signal analyzer VSA, and setting analysis signal parameters of the first vector signal analyzer VSA, so that the first vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P2; recording the EVM value obtained by the VSA measurement of the current first vector signal analyzer as EVMOTA，S1。
9. The method of claim 8, wherein the second testing system operates as follows:
setting a second vector signal generator VSG to output a digital modulation signal with the output power of P1; opening a second vector signal analyzer VSA, and setting analysis signal parameters of the second vector signal analyzer VSA, so that the second vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P3; adjusting attenuator size of second vector signal analyzer VSAGatt1(Gatt1 ≈ P3-P2), so that the power of the signal received by the second vector signal analyzer VSA after passing through the attenuator is equal to P2; recording the EVM value obtained by the VSA measurement of the current second vector signal analyzer as EVMOTA，S2。
10. The method of claim 9, wherein the third testing system operates as follows:
setting a third vector signal generator VSG to output a digital modulation signal, and outputting power P1; opening a third vector signal analyzer VSA, and setting analysis signal parameters of the third vector signal analyzer VSA, so that the third vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P4; adjusting the size of an attenuator of the third vector signal analyzer VSA to Gatt2, so that the size of the signal power received by the third vector signal analyzer VSA is equal to P2 after the signal power is subjected to the attenuator Gatt2(Gatt2 ≈ P4-P2); recording the EVM value measured by the VSA of the current third vector signal analyzer as EVMOTA,S3。
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