CN113484549B - EVM measuring method suitable for OTA test - Google Patents

Abstract

The invention discloses an EVM measurement method suitable for OTA testing, comprising the following steps: Step 1: Building different error vector magnitude measurement systems, the error vector magnitude measurement systems include a first measurement system, a second measurement system, a first measurement system, and a second measurement system. three measurement systems; step two, carry out error vector magnitude measurement under different error vector magnitude measurement systems; step three, obtain the error vector magnitude measurement values of different error vector magnitude measurement systems; step four, obtain according to different measurement systems Calculates the error vector magnitude caused by the DUT itself. This measurement method is suitable for OTA test conditions. By building three test links, the vector modulation error caused by instrument factors and the vector modulation error caused by environmental factors are calculated, and the above two interferences are eliminated by vector difference calculation. The more accurate vector modulation error of the device under test is obtained by calculation.

Description

An EVM measurement method suitable for OTA testing

technical field

The invention relates to the technical field of radio frequency terminal testing in the field of wireless communication, and relates to an EVM measurement method suitable for OTA testing.

Background technique

Error Vector Magnitude [Error Vector Magnitude, EVM], is the vector difference between the ideal reference signal and the measurement signal at a given time, is an important indicator to evaluate the signal quality after vector modulation in the communication system, and can intuitively reflect the difference between the measurement signal and the reference signal. Amplitude error, phase error. 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 Figure 1.

The Over The Air (OTA) test is to simulate the wireless transmission environment in a microwave anechoic chamber, and test the performance of the device under test 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 the antenna with the RF RRU module. The output port of the RF RRU module becomes the internal interface of the system, which makes it impossible to use the traditional conduction method to test. Instead, the far-field OTA test method is used to measure the EVM of the device under test.

For EVM testing of vector modulated signals, a vector signal generator (Vector Signal Generator, VSG) and a vector signal analyzer (Vector Signal Analyzer, VSA) must be used to measure the transmitter and receiver parts respectively. The nonlinear components (mixers and amplifiers) in the vector signal generator and vector signal analyzer will introduce different equipment measurement errors in the EVM measurement of the device under test under different output power and received power conditions, resulting in inaccurate measurement. The EVM measurement of the device under test, especially in the OTA test, due to the extremely large insertion loss of the test system, leads to a low power received by the VSA. Non-linear effects that interfere with the EVM measurement of the device under test.

In the prior art, only under the conduction method, the EVM test instrument is compensated for the error vector magnitude, and there is a lack of measuring and compensating the error vector magnitude error caused by the EVM test instrument itself under the OTA test condition (publication number CN 102546036 A, a compensation method for error vector magnitude); in addition, only considering the error vector magnitude error introduced by the vector signal analyzer VSA itself, but not considering that the vector signal generator VSG itself will also introduce error vector magnitude errors, resulting in measurement results. Inaccurate, there is instrument error (CN 110518988 A, a device and method for measuring device vector modulation error).

SUMMARY OF THE INVENTION

In view of the shortcomings of the above-mentioned prior art, the object of the present invention is to provide a method for measuring error vector magnitude under OTA test conditions, which is used to solve instrument factors under existing OTA test conditions, and environmental factors lead to inaccurate EVM measurement results Therefore, the accurate EVM value of the device under test can be obtained by measurement and calculation.

The present invention is realized by at least one of the following technical solutions.

An EVM measurement method suitable for OTA testing, including the following steps:

Step 1: Build different error vector magnitude measurement systems, the error vector magnitude measurement systems include a first measurement system, a second measurement system, and a third measurement system;

Step 2: Carry out error vector magnitude measurement under different error vector magnitude measurement systems;

Step 3: Obtaining the error vector magnitude measurement values of different error vector magnitude measurement systems;

Step 4: Calculate the error vector magnitude value caused by the device under test itself according to the error vector magnitude measurement values obtained under different measurement systems.

Preferably, the first measurement system includes a first vector signal generator VSG, a first vector signal analyzer VSA, the first No. 1 radio frequency cable, the first No. 2 radio frequency cable, the first test antenna No. 1, and the No. 1 radio frequency cable. 1. Test Antenna No. 2;

The second measurement system includes 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 under test DUT;

The third measurement system includes 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 first test antenna No. 1, the first test antenna No. 2 and the second test antenna have completely the same performance and appearance; the first No. 1 radio frequency cable, the first No. 2 radio frequency cable, and the second No. 1 radio frequency cable The No. 2 RF cable, the No. 2 RF cable, the No. 1 RF cable, and the No. 3 and No. 2 RF cable are the same length cables, and their performance and appearance are exactly the same.

Preferably, in the first measurement system, the direct measurement value of EVM is expressed as:

为在发射信号功率为P_TX1，接收信号功率为P_RX1条件下，第一矢量信号发生器VSG和第一矢量信号分析仪VSA共同引入的误差矢量幅度，

为第一测量系统OTA测试条件下第一测试天线1号引入的误差矢量幅度，

为第一测量系统OTA测试条件下第一测试天线2号引入的误差矢量幅度；Where EVM _{OTA, S1} is the direct measurement value of EVM under the first measurement system, P _TX1 is the power of the first vector signal generator VSG transmit signal, in dBm, P _RX1 is the power of the first vector signal analyzer VSA received signal size, in dBm,

is the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA under the condition that the transmitted signal power is P _TX1 and the received signal power is P _RX1 ,

is the error vector magnitude introduced by the first test antenna No. 1 under the OTA test condition of the first measurement system,

For the error vector magnitude introduced by the first test antenna No. 2 under the OTA test condition of the first measurement system;

In the second measurement system, the direct measurement of EVM is expressed as:

为在第二矢量信号发生器VSG发射信号功率为P_TX2条件下，待测器件引入的误差矢量幅度，

为第二测量系统OTA测试条件下，第二测试天线引入的误差矢量幅度；

代表待测器件的射频模块引入的误差矢量幅度，

代表待测器件的天线模块引入的误差矢量幅度，

和

共同构成待测仪器的误差适量幅度EVM_DUT(P_TX2)。Where EVM _{OTA, S2} is the direct measurement value of EVM under the second measurement system,

is the magnitude of the error vector introduced by the device under test under the condition that the transmitted signal power of the second vector signal generator VSG is P _TX2 ,

is the error vector magnitude introduced by the second test antenna under the OTA test condition of the second measurement system;

represents the magnitude of the error vector introduced by the RF module of the device under test,

represents the magnitude of the error vector introduced by the antenna module of the device under test,

and

Together they form the EVM _DUT (P _TX2 ) of the magnitude of error amount of the instrument under test.

In the third measurement system, the direct measurement of EVM is expressed as:

Wherein EVM _{OTA, S3} is the direct measurement value of EVM under the third measurement system, P _RX3 is the power of the third vector signal generator VSG transmit signal, P _TX3 is the power of the third vector signal analyzer VSA received signal, after The three measurement systems are measured to obtain EVM direct measurement values EVM _OTA,S1 , EVM _OTA,S2 , EVM _OTA,S3 .

Preferably, the distance L1 measured by the first measurement system is the same as the distance L2 measured by the second measurement system.

Preferably, the transmission signal power of the vector signal generator VSG of each measurement system is the same, P _TX1 =P _TX2 =P _TX3 ; the received signal power of the vector analyzer VSA of each measurement system is kept the same, P _RX1 =P _RX2 =P _RX3 .

为：Preferably, the EVM measurement value of the component under test

for:

Preferably, the first measurement system operates as follows:

Set the first vector signal generator VSG to output a digital modulation signal and output power P1; turn on the first vector signal analyzer VSA, and set the first vector signal analyzer VSA to analyze the signal parameters, so that the first vector signal analyzer VSA can demodulate normally Receive the signal, and the received signal power is P2 at this time; record the EVM value measured by the current first vector signal analyzer VSA, which is EVM _OTA,S1 .

Preferably, the second test system operates as follows:

Set the second vector signal generator VSG to output a digital modulation signal, and the output power is P1; open the second vector signal analyzer VSA, and set the second vector signal analyzer VSA to analyze the signal parameters, so that the second vector signal analyzer VSA can solve the problem normally. Adjust the received signal, at this time the received signal power is P3; adjust the attenuator size of the second vector signal analyzer VSA to Gatt1 (Gatt1≈P3-P2), so that after the attenuator, the second vector signal analyzer VSA receives The signal power is equal to P2; record the EVM value measured by the current second vector signal analyzer VSA, which is EVM _OTA,S2 .

Under the third test system, the digital modulation signal generated by the third vector signal generator VSG directly enters the third vector signal analyzer through the third No. 1 RF cable and the third No. 2 RF cable in the form of conduction. The receiving port of the VSA.

The third test system operates as follows:

Set the third vector signal generator VSG to output a digital modulation signal and output power P1; turn on the third vector signal analyzer VSA, and set the third vector signal analyzer VSA to analyze the signal parameters, so that the third vector signal analyzer VSA can demodulate normally Receive the signal, at this time the received signal power is P4; adjust the attenuator size of the third vector signal analyzer VSA to Gatt2, so that Gatt2 (Gatt2≈P4-P2), after passing through the attenuator, the third vector signal analyzer VSA The received signal power is equal to P2; the EVM value measured by the current third vector signal analyzer VSA is recorded as EVM _OTA,S3 .

Substitute the directly measured EVM values measured under the conditions of the three measurement systems into formula (4) to calculate the measured EVM values of the device under test.

This measurement method is suitable for OTA test conditions. By building three test links, the vector modulation error caused by instrument factors and the vector modulation error caused by environmental factors are calculated, and the above two interferences are eliminated by vector difference calculation. The more accurate vector modulation error of the device under test is obtained by calculation.

Compared with the prior art, the beneficial effects of the present invention are:

An EVM measurement method based on OTA test conditions is provided for the antenna front-end integrated DUT or multi-channel DUT. Compared with the EVM measurement method applied under the condition of the conduction method, the present invention is suitable for the OTA measurement condition, and can simultaneously test the instruments under test with multiple transceiver channels, thereby improving the EVM test speed, and the test conditions are closer to those under test. The actual working conditions of the instrument.

Description of drawings

Fig. 1 is the definition schematic diagram of the vector modulation error involved in the method of the present invention;

2 is a schematic diagram of a first measurement system according to an embodiment of the present invention;

3 is a schematic diagram of a second measurement system according to an embodiment of the present invention;

4 is a schematic diagram of a third measurement system according to an embodiment of the present invention;

Fig. 5 is the EVM measurement flow chart of the 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 ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the following examples are given to further describe the present invention in detail.

Embodiment 1:

An EVM measurement method suitable for OTA testing, including the following steps:

Step 1: EVM measurement systems with different construction methods; the EVM measurement system includes a first measurement system, a second measurement system, and a third measurement system;

The construction method of the first measurement system is shown in Figure 2, S1 represents the first measurement system S1 includes the first vector signal generator VSG, the first vector signal analyzer VSA, the first No. 1 radio frequency cable, and the first No. 2 radio frequency Cable, first test antenna No. 1, first test antenna No. 2. The first vector signal generator VSG is connected to the first test antenna No. 1 through the No. 1 radio frequency cable, and the modulated signal generated by the first vector signal generator VSG propagates to the free space through the first test antenna No. 1; the first vector signal The signal analyzer VSA is connected to the first test antenna 2 through the No. 1 and No. 2 radio frequency cables. 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 is L. The first test antenna No. 2 will The received modulated signal is transmitted to the VSA for signal demodulation;

The construction method of the second measurement system is shown in Figure 3. The second measurement system S2 includes a second vector signal generator VSG, a second vector signal analyzer VSA, a second No. 1 radio frequency cable, and a second No. 2 radio frequency cable , the second test antenna, the device under test DUT. The second vector signal generator VSG is connected to the DUT through the second RF cable No. 1, and the modulated signal generated by the second vector signal generator VSG propagates to free space through the DUT; the second vector signal analyzer VSA passes through the second The No. 2 radio frequency cable is connected to the second test antenna. The horizontal distance between the antenna aperture plane of the DUT and the second test antenna aperture plane is L, and the second test antenna transmits the received modulated signal to the VSA for signal demodulation;

The construction method of the third measurement system is shown in Figure 4. The third measurement system S3 includes the third vector signal generator VSG, the third vector signal analyzer VSA, the third No. 1 radio frequency cable, and the third No. 2 radio frequency cable . The modulated signal generated by the third vector signal generator VSG reaches the receiving port of the third vector signal analyzer VSA through the third No. 1 radio frequency cable and the third No. 2 radio frequency cable, and the third vector signal analyzer VSA receives the signal demodulation;

In the measurement systems S1, S2 and S3, the first test antenna No. 1, the first test antenna No. 2 and the second test antenna have completely the same performance and appearance; the first No. 1 radio frequency cable, the first No. 2 radio frequency cable , the second No. 1 radio frequency cable, the second No. 2 radio frequency cable, the third No. 1 radio frequency cable, and the third No. 2 radio frequency cable are all cables of the same length;

Step 2. Establish the relationship between instrument factors, environmental factors and EVM;

In the first measurement system, the direct measurement of EVM is expressed as:

为在发射信号功率为P_TX1，接收信号功率为P_RX1条件下，第一矢量信号发生器VSG和第一矢量信号分析仪VSA共同引入的误差矢量幅度，

为在OTA测试距离为L的条件下第一测试天线1号引入的误差矢量幅度，

为OTA测试距离为L的条件下第一测试天线2号引入的误差矢量幅度，由于第一测试天线1号与第一测试天线2号为完全相同的天线，所以

大小等于

Where EVM _{OTA, S1} is the direct measurement value of EVM under the first measurement system, P _TX1 is the power of the first vector signal generator VSG transmit signal, in dBm, P _RX1 is the first vector signal analyzer VSA received signal Power level, in dBm,

is the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA under the condition that the transmitted signal power is P _TX1 and the received signal power is P _RX1 ,

is the error vector magnitude introduced by the first test antenna No. 1 under the condition that the OTA test distance is L,

It is the error vector magnitude introduced by the first test antenna No. 2 under the condition that the OTA test distance is L. Since the first test antenna No. 1 and the first test antenna No. 2 are exactly the same antenna, so

size equal to

In the second measurement system, the direct measurement of EVM is expressed as:

为在第二矢量信号发生器VSG发射信号功率为P_TX2条件下，待测器件引入的误差矢量幅度。

代表在第二矢量信号发生器VSG发射信号功率为P_TX2条件下,待测器件的射频模块引入的误差矢量幅度，

代表待测器件的天线模块引入的误差矢量幅度，两者共同构成待测仪器的误差适量幅度，如公式(3)所表达。Among them, EVM _{OTA, S2} is the direct measurement value of EVM under the second measurement system,

It is the magnitude of the error vector introduced by the device under test under the condition that the transmitted signal power of the second vector signal generator VSG is P _TX2 .

represents the magnitude of the error vector introduced by the RF module of the device under test under the condition that the transmitted signal power of the second vector signal generator VSG is P _TX2 ,

Represents the magnitude of the error vector introduced by the antenna module of the device under test, and the two together constitute the magnitude of the proper amount of error of the instrument under test, as expressed by formula (3).

In the third measurement system, the direct measurement of EVM is expressed as:

Among them, EVM _{OTA, S3} is the direct measurement value of EVM under the third measurement system.

表示为：After the measurement of three measurement systems, the EVM direct measurement values EVM _{OTA, S1} , EVM _{OTA, S2} , EVM _{OTA, S3} are obtained. Through formula (1) to formula (4), the transmit power of the VSG in the vector signal generator is calculated as P Measured EVM of the device under test under _TX conditions

Expressed as:

Step 3: Carry out EVM measurement under different measurement systems;

λ为电磁波的波长，D为第一测试天线2号的孔径。第一测量系统操作如下：Under the first measurement system, the digital modulation signal generated by the first vector signal generator VSG is converted into electromagnetic waves propagating in free space through the first test antenna No. 1, and received by the first test antenna No. 2 with a distance of L. Where L is the horizontal distance between the first test antenna No. 1 aperture plane and the first test antenna No. 2 aperture plane, and the size of L must reach the far-field conditional distance of the first test antenna No. 2,

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:

Set the first vector signal generator VSG to output a digital modulation signal and output power P1; turn on the first vector signal analyzer VSA, and set the first vector signal analyzer VSA to analyze the signal parameters, so that the first vector signal analyzer VSA can demodulate normally Receive the signal, and the received signal power is P2 at this time; record the EVM value measured by the current first vector signal analyzer VSA, which is EVM _OTA,S1 .

Under the S2 test system, the digital modulation signal generated by the second vector signal generator VSG is converted into electromagnetic waves propagating in free space through the device under test DUT, and received by the second measurement antenna No. 2 with a distance of L, where L is The horizontal distance between the DUT's own antenna aperture plane and the second test antenna aperture plane; the second vector signal generator VSG decomposes the received signal into I, Q component signals, and obtains the I, Q component signals and ideal demodulation by decomposing The I in the state is compared and calculated to obtain the required direct measurement of EVM.

The S2 test system operates as follows:

Set the second vector signal generator VSG to output a digital modulation signal, and the output power is P1; open the second vector signal analyzer VSA, and set the second vector signal analyzer VSA to analyze the signal parameters, so that the second vector signal analyzer VSA can solve the problem normally. Adjust the received signal, at this time the received signal power is P3; adjust the attenuator size of the second vector signal analyzer VSA to Gatt1 (Gatt1≈P3-P2), so that after the attenuator, the second vector signal analyzer VSA receives The magnitude of the signal power is approximately equal to P2; record the EVM value measured by the current second vector signal analyzer VSA, which is EVM _OTA,S2 .

Under the S3 test system, the digital modulation signal generated by the third vector signal generator VSG directly enters the third vector signal analyzer VSA through the No. 1 RF cable No. 1 and No. 2 RF cable in the form of conduction. the receive port.

The S3 test system operates as follows:

Set the third vector signal generator VSG to output a digital modulation signal and output power P1; turn on the third vector signal analyzer VSA, and set the third vector signal analyzer VSA to analyze the signal parameters, so that the third vector signal analyzer VSA can demodulate normally Receive the signal, the received signal power is P4 at this time; adjust the attenuator size of the third vector signal analyzer VSA to Gatt2, so that Gatt2≈P4-P2, after passing through the attenuator, the third vector signal analyzer VSA receives The signal power is approximately equal to P2; record the EVM value measured by the current third vector signal analyzer VSA, which is EVM _{OTA, S3} .

本发明的测量方式在OTA条件下，消除了仪器因素与环境因素对待测器件EVM测量造成的影响。Substitute the directly measured EVM values measured under the conditions of the three measurement systems into formula (5), and eliminate the vector modulation error caused by instrument factors and the vector modulation error caused by environmental factors through calculation, and obtain the device under test itself. The vector modulation error of

Under the OTA condition, the measurement method of the present invention eliminates the influence caused by the instrument factor and the environmental factor to measure the EVM of the device under test.

Embodiment 2:

According to the schematic diagrams of the first measurement system (S1), the second measurement system (S2), and the third measurement system (S3) in Figure 2, Figure 3, and Figure 4, build an EVM measurement system, set up a vector signal generator and a vector signal analyzer System parameters, the specific configuration of equipment hardware and software conditions are shown in Table 1 and Table 2:

(1) Vector signal generator SMW200A

Table 1 SMW200A parameter configuration diagram

(2) Vector Signal Analyzer R&S FSW43

Table 2 R&S FSW43 parameter configuration diagram

(3) The first test antenna No. 1, the first test antenna No. 2, and the second test antenna of the three measurement systems are all LB-180400-KF multi-octave horn antennas of AB Microwave;

As shown in Figure 5, the described operation method for EVM measurement applicable to OTA testing includes the following steps:

Step 101: Set the output power of the vector signal generator, and record the current output power P1 of the vector signal generator, the power signal P2 received by the vector signal analyzer, and the measured value of EVM. The results of 5 repeated measurements and the average calculation results are shown in Table 3.

Table 3 is based on the experimental measurement results and calculation results under the operation of step 101

Step 102: Set the output power of the vector signal generator, keep the current output power of the vector signal generator as P1, and set the size of the attenuator Gatt1 according to the size of the power signal P3 received by the vector signal analyzer, so that P3-Gatt2≈P2 The results of 5 repeated measurements and the average calculation results are shown in Table 4.

Table 4 is based on the experimental measurement results and calculation results under the operation of step 102

Step 103: Set the output power of the vector signal generator, keep the current output power of the vector signal generator as P1, and set the size of the attenuator Gatt2 according to the size of the power signal P4 received by the vector signal analyzer, so that P4-Gatt2≈P2 The results of 5 repeated measurements and the average calculation results are shown in Table 5.

Table 5 is based on the experimental measurement results and calculation results under the operation of step 103

For the present embodiment, the EVM _{OTA is obtained through measurement in steps 101 to 103, S1} =7.88%, EVM _{OTA, S2} =9.53%, and EVM _{OTA, S3} =7.20%. After the calculation of formula (4), the vector error caused by the device under test itself under the OTA test is obtained as

Embodiment 3:

In order to verify the accuracy of the EVM measurement results of the present invention, the DUT composition of the device under test adopted in Example 2 is shown in Figure 6, which consists of three parts: DUT radio frequency module, DUT antenna and DUT radio frequency cable; DUT radio frequency cable connection With the DUT RF module and the DUT antenna, the DUT RF module and the DUT antenna can be separated by removing the DUT RF cable. The DUT RF module is composed of an LNA power amplifier module, and the DUT antenna is a multi-octave horn antenna of AB Microwave. -180400-KF, which is the same as the antenna used in Example 2, and the DUT radio frequency cable is the same as that used in Example 2.

通过公式(1)～公式(4)计算得到在矢量信号发生器VSG发射功率为P_TX条件下，待测器件中DUT射频模块EVM值

表示为：Since the DUT antenna is the same as the antenna used in Embodiment 2, it can be considered that

The EVM value of the DUT radio frequency module in the device under test is calculated by formula (1) to formula (4) under the condition that the VSG transmit power of the vector signal generator is P _TX

Expressed as:

Using the data measured in Example 2, through the calculation of formula (5), it is obtained that the vector error caused by the DUT radio frequency module of the device under test under the OTA test is:

Conduct EVM measurement on DUT RF module using conduction method, the measurement result is 5.23%

For the DUT radio frequency module, compare the EVM measurement results of the conduction method with the EVM measurement results of the present invention, and the data comparison is shown in Table 6:

Table 6 Comparison of EVM measurement results of conduction method and EVM measurement results of the present invention

Conductive EVM measurement EVM measurement of the present invention difference between the two EVM (%) 5.23 5.36 0.13

From the test results of Example 3, it can be shown that in the OTA test system, using three different hardware connection methods, the error vector value of the DUT radio frequency module in the instrument under test is obtained separately, and the difference between the results obtained by the conduction method is 0.13%, can be considered to be within the experimental error range.

This embodiment adopts an EVM measurement method suitable for an OTA test environment. Through three different hardware connection methods, the influence of equipment factors and environmental factors on the EVM measurement of the device under test is excluded, and the magnitude of the error vector caused by the device under test itself is calculated. A new EVM measurement method is provided for the device under test that integrates the antenna and the RF module.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can use the methods and technical contents disclosed above to improve the present invention without departing from the spirit and scope of the present invention. The technical solutions are subject to possible changes and modifications. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention belong to the technical solutions of the present invention. protected range.

Claims (7)

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; the first measurement system comprises a first vector signal generator VSG, a first vector signal analyzer VSA, a first No. 1 radio frequency cable, a first No. 2 radio frequency cable, 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;

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;

step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained under different measurement systems, wherein in the first measurement system, the direct measured value EVM of the EVM _OTA,s1 Expressed as:

wherein EVM _OTA,S1 Is a direct measure of the EVM under the first measurement system, P _TX1 Is the magnitude of the power of the signal transmitted by the first vector signal generator VSG in dBm, P _RX1 The value of the power of the received signal, in dBm,

to transmit at a signal power of P _TX1 Received signal power of P _RX1 Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,

the error vector magnitude introduced for the first test antenna No. 1 under the first measurement system OTA test condition,

the error vector magnitude introduced for the first test antenna No. 2 under the OTA test condition of the first measurement system;

in a second measuring system, direct measurement of EVM _OTA,S2 Expressed as:

wherein EVM _OTA,S2 Is a direct measure of EVM under the second measurement system,

for transmitting at the second vector signal generator VSGPower of transmitted signal is P _TX2 Under the condition, the error vector amplitude introduced by the device to be tested,

the error vector magnitude introduced by the second test antenna under the OTA test condition of the second measurement system;

representing the magnitude of the error vector introduced by the rf module of the device under test,

representing the magnitude of the error vector introduced by the antenna module of the device under test,

and

error proper amplitude EVM (error vector magnitude) jointly forming instrument to be measured _DUT (P _TX2 )；

Direct measurement of EVM in a third measurement System, EVM _OTA,S3 Expressed as:

wherein EVM _OTA,S3 Is a direct measure of EVM under a third measurement system, P _RX3 Magnitude of power of signal transmitted for third vector signal generator VSG, P _TX3 The power of the VSA receiving signal of the third vector signal analyzer is measured by three measuring systems to obtain the direct measurement value EVM of the EVM _OTA,S1 、EVM _OTA,S2 、EVM _OTA,S3 ；

And the EVM measurement value of the device under test

Formula for calculationThe following:

2. the EVM measuring method suitable for OTA test according to claim 1, 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 No. 1 radio frequency cable, the first No. 2 radio frequency cable, the second No. 1 radio frequency cable, the second No. 2 radio frequency cable, the third No. 1 radio frequency cable and the third No. 2 radio frequency cable are isometric cables of the same type, and the performance and the appearance are completely consistent.

3. The EVM measurement method applicable to OTA tests according to claim 2, characterized in that the distance L1 measured by the first measurement system is the same size as the distance L2 measured by the second measurement system.

4. An EVM measurement method suitable for OTA tests according to claim 3, characterized in that each measurement system vector signal generator VSG has a uniform transmission signal power, P _TX1 ＝P _TX2 ＝P _TX3 (ii) a Keeping VSA receiving signal power of each measuring system consistent, P _RX1 ＝P _RX2 ＝P _RX3 。

5. The EVM measurement method applicable to OTA testing according to claim 4, 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 a 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 measured by the VSA of the first vector signal analyzer as the EVM _OTA,S1 。

6. The EVM measurement method applicable to OTA testing according to claim 5, 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 the 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 equal to P2 after the attenuator; recording the EVM value measured by the VSA of the current second vector signal analyzer as the EVM _OTA,S2 。

7. A method of EVM measurement suitable for OTA testing according to claim 6, wherein the third testing system operates as follows:

setting a third vector signal generator VSG to output a digital modulation signal and output 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(Gatt2 ≈ P4-P2) can ensure that the power of a signal received by the third vector signal analyzer VSA is equal to P2; recording the EVM value measured by the VSA of the current third vector signal analyzer as EVM _OTA,S3 。

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