A method for determining the parameters of an anechoic chamber

Abstract

This invention relates to the field of radio frequency testing technology and provides a method for determining the parameters of an anechoic chamber, comprising: S1, measuring the value of the interference signal level I under unshielded conditions; S2, determining the pre-received signal level P and the uncertainty component of the magnitude of P due to co-channel interference; S3, calculating the shielding attenuation A of the shielded chamber based on the signal-to-interference ratio. I Alternatively, the shielding attenuation A of the shielded room can be calculated based on the increase in background noise. N Or calculate the shielding attenuation A of strong electromagnetic interference. p In practical engineering, if it is necessary to use all three shielding attenuation requirement values ​​simultaneously, or even just two of them, the maximum value should be used. This invention also enables the calculation of the quiet zone reflection level requirement of an anechoic chamber based on the measurement uncertainty of the antenna pattern. This invention creatively provides a method for determining the parameters of a shielded chamber and an anechoic chamber, overcoming the shortcomings of traditional methods that rely solely on experience to determine relevant parameters.

Description

Technical Field

[0001] This invention relates to the field of radio frequency testing technology, and in particular to a method for determining the parameters of an anechoic chamber. Background Technology

[0002] In radio frequency (RF) testing, in some cases, to eliminate the influence of external signals on the test, it is necessary to conduct the test in a shielded room. What are the requirements for shielding attenuation during testing? The answer to this question is important not only for testing laboratories but also frequently involves many laboratory accreditation activities. Some refer to electromagnetic compatibility (EMC) standards and believe that the shielding attenuation of the shielded room should be greater than 80 dB, while others refer to the technical requirements for military electromagnetic shielding and believe that the shielding attenuation should be greater than 100 dB. These understandings are based on fixed specifications, and these differing perspectives have caused confusion in testing and quality activities.

[0003] Furthermore, an anechoic chamber is a device used to test and measure electromagnetic wave performance. It uses absorbing materials to eliminate electromagnetic wave reflections from walls, ceilings, and floors to simulate an open space environment. The quiet zone refers to the reflection level within the anechoic chamber, specifically the area used to measure antenna performance. Quiet zone reflection level generally refers to the ratio of the strongest reflected multipath propagation path to the direct path in the electromagnetic wave propagation within the anechoic chamber. Achieving high-quality quiet zone reflection level specifications requires more space and superior absorbing materials, which undoubtedly leads to higher costs. The problem is that a clear calculation method has long been lacking regarding the specific quiet zone reflection level specifications required for antenna measurements.

[0004] This invention aims to propose a testing and evaluation method to determine reasonable shielding attenuation requirements. Similarly, for shielded equipment rooms that need to be protected against external electromagnetic interference or electromagnetic attacks, reasonable shielding attenuation requirements also need to be determined using appropriate calculation methods. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for determining the parameters of an antenna anechoic chamber.

[0006] The present invention adopts the following technical solution:

[0007] A method for determining parameters of an anechoic chamber, the anechoic chamber comprising a shielded area and a quiet area, the method comprising:

[0008] S1. Measure the value of the interference signal level I under unshielded conditions;

[0009] S2. Determine the pre-received signal level P, and the uncertainty component of the magnitude of P due to co-channel interference;

[0010] S3. Based on the results of steps S1 and S2, calculate the shielding attenuation A of the shielded room based on the signal-to-interference ratio.I Alternatively, the shielding attenuation A of the shielded room can be calculated based on the increase in background noise. N , or shielding attenuation of strong electromagnetic interference A p ,

[0011] In addition to any of the possible implementations described above, another implementation is provided where, in practical engineering, if it is necessary to use all three shielding attenuation requirement values ​​simultaneously, or even just two of them, the maximum value should be taken.

[0012] In addition to any of the possible implementations described above, another implementation is provided in which, in step S3, the shielding attenuation requirement A of the shielded room is calculated based on the signal-to-interference ratio. I Specifically:

[0013]

[0014] Where I represents the interference signal level under unshielded conditions, P represents the pre-received signal level, and u I [dB] represents the uncertainty component introduced by the interference signal.

[0015] In addition to any of the possible implementations described above, another implementation is provided in which, in step S3, when the uncertainty components of the pre-received signal level P and the magnitude of the co-channel interference on P are difficult to estimate, the shielding attenuation requirement A of the shielded room is calculated based on the increase in noise floor. N Specifically:

[0016]

[0017] Where I is the interference signal level under unshielded conditions, and K is the Boltzmann constant, taken as 1.38 × 10⁻⁶. -23 B is the signal bandwidth, T is the thermodynamic temperature, and u N The allowable rise limit of the equivalent noise floor after the introduction of external interference, taken as u. N =0.4dB~5dB.

[0018] In addition to any of the possible implementations described above, another implementation is provided in which, in step S2, the pre-received signal level P and the uncertainty component of the magnitude of P due to co-channel interference are obtained through test standards or measurement practices.

[0019] In addition to any of the possible implementations described above, another implementation is provided in which the value of the interference signal level I under the unshielded condition in step S1 is obtained by the following method:

[0020] Under unshielded conditions, the spectrum analyzer is connected to the receiving antenna via a cable. The cable is the same as that used in the actual test in the shielded room. An omnidirectional antenna is selected for the receiving antenna. The spectrum analyzer is set to the frequency band and bandwidth corresponding to the test item. The channel power function is used to measure the interference signal level. Measurements are taken 5 to 20 times under different time, location, and antenna polarization directions, and the maximum value is taken.

[0021] In addition to any of the possible implementations described above, another implementation is provided in which, in step S2, the co-channel interference is strong electromagnetic interference outside the shielded room. In this case, the shielding attenuation requirement A of the shielded room for this type of strong electromagnetic interference is... p for:

[0022] A p [dB] = E out [dBV / m]-E s [dBV / m];

[0023] Among them, E s The threshold field strength for a sensitive device to withstand a certain electromagnetic interference in an unshielded environment, measured in dBV / m, is obtained through actual measurement or the equipment's design specifications; E out This refers to the interference field strength generated by this type of strong electromagnetic interference at a location immediately adjacent to the shielded room outside the shielded room. The unit of measurement is dBV / m, and this value is obtained through measurement or evaluation simulation. If the calculated A... p If the value is less than or equal to 0 dB, then no shielding is required.

[0024] In addition to any of the possible implementations described above, another implementation is provided in which the strong electromagnetic interference outside the shielded area includes DC electromagnetic fields, continuous wave electromagnetic fields, modulated signal electromagnetic fields, and pulse electromagnetic fields.

[0025] In addition to any of the possible implementations described above, another implementation is provided, wherein the anechoic chamber parameters include the quiet zone reflection level, and the quiet zone reflection level requirement of the anechoic chamber is calculated based on the antenna pattern measurement uncertainty. The specific method is as follows:

[0026] Suppose the expected value of a certain antenna parameter being measured is A. s dB, the quiet zone reflection level is QdB, and the ratio of the voltage amplitude of the reflected wave to the direct wave formed at the antenna receiving port is called the reflection-to-direct-wave ratio RDR:

[0027] RDR[dB]=QA s ;

[0028] The linear dimensionless form of the amplitude of the direct reflection ratio (RDR) is M. RDR :

[0029]

[0030] Due to the presence of reflected waves, the actual received signal differs from the ideal situation. Assuming the ideal received signal voltage vector is 1, then the voltage vector of the received signal with reflected waves is:

[0031]

[0032] Voltage phase of the reflected wave It is a random quantity that is uniformly distributed within the range of 0 to 360°;

[0033] The error in the actual measured power is:

[0034]

[0035] The maximum and minimum values ​​of its error are E r-max and E r-min :

[0036] E r-max =20lg|1+M RDR |

[0037] E r-min =20lg|1-M RDR |

[0038] The standard uncertainty component U introduced by reflection R for:

[0039]

[0040] Where k is the expansion factor, empirically set to 2 or 3; calculate the standard uncertainty component u introduced by reflection under different direct reflection ratios. R The mapping relationship and mapping curve between the quiet zone reflection level and the standard uncertainty component of the antenna pattern are obtained, and the required quiet zone reflection level is found based on the desired standard uncertainty component.

[0041] In addition to any of the possible implementations described above, another implementation is provided where, when the antenna under test is within the quiet zone, the taper parameter corresponding to the furthest distance the antenna deviates from the center of the quiet zone is T. a The dimension is dB; the uncertainty component of the pattern measurement introduced by the taper is u. T [dB] is obtained through simulation or measurement.

[0042] All uncertainty components can be synthesized by summing their squares and taking the square root. This synthesized uncertainty is used to evaluate the accuracy of the final RF and antenna measurement results.

[0043] The beneficial effects of this invention are as follows: This invention creatively provides a method for determining the parameters of shielded rooms and anechoic chambers, overcoming the shortcomings of traditional methods that rely solely on experience to determine relevant parameters. According to this invention, in radio frequency and microwave electromagnetic field related tests, the required shielding effectiveness can be determined scientifically and quantitatively, rather than rigidly specifying shielding effectiveness according to fixed indicators based on some experience. On the one hand, this ensures the scientific and rational nature of the test and the accuracy of radio frequency test results; on the other hand, in some cases, excessively high requirements for shielding effectiveness can be scientifically relaxed, thereby reducing the construction cost of the shielded room. For shielded equipment rooms that need to protect against external electromagnetic interference or electromagnetic attacks, the calculation method of this invention can determine reasonable shielding attenuation requirements.

[0044] Similarly, in antenna and electromagnetic field related tests, this invention enables the scientific and quantitative calculation of the required quiet zone reflection level for the anechoic chamber, rather than rigidly determining the quiet zone reflection level requirements based on fixed indicators derived from experience. This ensures the scientific validity and rationality of the test results, guaranteeing the uncertainty level of antenna and electromagnetic field related measurements. Furthermore, in some cases, empirical requirements for the quiet zone reflection level may be excessively high. Achieving such high quiet zone reflection levels requires more space and larger volumes of absorbing material, undoubtedly leading to unnecessary cost increases. The calculation method proposed in this invention scientifically avoids excessively high requirements for the quiet zone reflection level, thereby reasonably reducing the construction cost of the anechoic chamber. Attached Figure Description

[0045] Figure 1 The general model for radio frequency conductedion testing is shown.

[0046] Figure 2 The image shows a test apparatus for evaluating interference signals in an embodiment.

[0047] Figure 3 The image shows direct and reflected waves in antenna measurements.

[0048] Figure 4 The figure shows the voltage vector of the received signal in the presence of reflected waves.

[0049] Figure 5 The figure shows the error contribution and its probability density curve in the embodiment (reflection direct ratio = -14dB).

[0050] Figure 6 The figure shows the error contribution and its probability density curve in the embodiment (reflection direct ratio = -27dB).

[0051] Figure 7 The figure shows the effect of the direct reflection ratio on the standard uncertainty component in the embodiment.

[0052] Figure 8 The figure shows the effect of the quiet zone reflection level on the standard uncertainty component in the embodiment (expected value of the measured pattern parameter -25dB).

[0053] Figure 9 The figure shows the effect of the quiet zone reflection level on the standard uncertainty component in the embodiment (expected value of the measured pattern parameter -17dB).

[0054] Figure 10 The diagram shown is a flowchart illustrating a method for determining the parameters of an anechoic chamber according to an embodiment of the present invention. Detailed Implementation

[0055] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, but can be combined with each other to achieve better technical effects.

[0056] An anechoic chamber consists of a shielded area and a quiet area. The parameters of an anechoic chamber include the shielding attenuation requirement for evaluating the effectiveness of the shielded area and the quiet area reflection level for evaluating the performance of the quiet area.

[0057] An embodiment of the present invention provides a method for determining the parameters of an anechoic chamber, such as... Figure 10 As shown, it includes:

[0058] S1. Measure the value of the interference signal level I under unshielded conditions;

[0059] S2. Determine the pre-received signal level P, and the uncertainty component of the magnitude of P due to co-channel interference;

[0060] S3. Calculate the shielding attenuation A of the shielded room based on the signal-to-interference ratio. I Alternatively, the shielding attenuation A of the shielded room can be calculated based on the increase in background noise. N Or calculate the shielding attenuation requirement A for strong electromagnetic interference. p In actual engineering projects, if it is necessary to use the values ​​of these three shielding attenuation requirements simultaneously or the values ​​of two of them, the maximum value shall be taken.

[0061] I. Calculation of shielding effectiveness requirements for shielded rooms based on signal-to-interference ratio

[0062] Assume the expected minimum signal level to be received in the RF test is P, the interference signal level in the unshielded condition is I, and the shielding attenuation of the shielded chamber in the interference signal frequency band is A. I The signal-to-interference ratio (SIR) during testing in a shielded room is:

[0063]

[0064] Co-channel interference introduces an uncertainty component into the value of P, which can be evaluated using equation (2).

[0065]

[0066] u I The smaller the better, but infinitely small is unnecessary in engineering, especially when the desired signal level is low. I It is reasonable to compare the repeatability or accuracy requirements of the readings of P itself with those of the test. Combining equations (1) and (2), we can obtain:

[0067]

[0068] Obviously, when the pre-received signal levels P and u I When the requirements and the interference signal level I are determined, the shielding attenuation A is... I The requirements are calculable, including the pre-received signal levels P and u. I The requirements can be obtained through testing standards and measurement practices. The key is to obtain the level I of the interference signal under unshielded conditions.

[0069] II. In the pre-received signal levels P, u I When demand is difficult to estimate, an assessment method based on the increase in background noise is used.

[0070] The known noise floor of the radio frequency signal is:

[0071] P N =FKBT (4)

[0072] Where F is the equivalent linear value of the signal-to-noise figure, which can be taken as 1 for rigorous evaluation purposes. K is the Boltzmann constant, which can be taken as 1.38 × 10⁻⁶. -23 B is the signal bandwidth, and T is the thermodynamic temperature, which can be taken as 290 Kelvin at room temperature. After the introduction of external interference, the equivalent noise floor will increase; let its allowable increase limit be u. N .

[0073]

[0074] Combining equation (4), we can obtain:

[0075]

[0076] In the field of wireless communication, for rigorous evaluation, u can be adopted. N=0.4dB~5dB, and the additional interference power at 0.4dB is approximately 9.6% of the noise floor power. Theoretically, the method in equation (6) is more stringent than the method in equation (3). Different estimation methods are proposed to adapt to the available conditional information, such as the different attenuation requirements obtained by different methods. For the sake of prudence, the larger value is adopted.

[0077] III. Methods for Evaluating Interference Signal Levels

[0078] Obviously, regardless of the estimation method, the value of the interference signal level I under unshielded conditions must first be obtained. The following proposes a method for measuring and evaluating interference signals.

[0079] The general model for conduction testing is as follows: Figure 1 As shown, the core elements are the transmitter, cables, and receiver.

[0080] In testing, sometimes the transmitter acts as the standard and the receiver as the test subject, and sometimes the receiver acts as the standard and the transmitter as the test subject. There are three paths for external electromagnetic interference to couple through: 1. Transmitter. 2. Cable. 3. Receiver. From the perspective of coupling effects, there are the following:

[0081] 1. Electromagnetic waves are coupled into the cable through its shielding layer.

[0082] 2. Electromagnetic waves are coupled to the radio frequency circuit board through the housing of the transmitter and receiver.

[0083] 3. If an antenna is present at the receiving end, coupling is received through the antenna.

[0084] Interference power coupled in through the first and second effects is very small: cables, especially commonly used coaxial cables, have good shielding effectiveness, and the metal casings of instruments and RF equipment themselves constitute shielding cavities. Therefore, the most significant interference enters through antenna coupling. A typical scenario is when measuring the sensitivity of a mobile terminal, a mobile communication integrated tester is connected to the terminal under test via conduction. In this case, the mobile terminal's antenna may still be active and connected to the RF port. Therefore, if an antenna is used to measure the received power inside the shielded room, it can reflect the most stringent external interference indicators, hence the following evaluation method.

[0085] Without blocking, according to Figure 2 Configure the test setup. The cables used here are identical to those used in the actual test in the shielded room. An omnidirectional antenna is selected as the receiving antenna. The spectrum analyzer is set to the frequency band and bandwidth corresponding to the test item. The channel power function is used to measure the interference signal level. Measurements are taken 5 to 20 times under different time, location, and antenna polarization conditions, and the maximum value is recorded. Generally, this evaluation includes a margin of safety.

[0086] IV. Calculating the shielding effectiveness requirements of the shielded room based on electromagnetic protection requirements

[0087] Suppose that sensitive equipment in a shielded room may be affected by strong electromagnetic interference outside the shielding room. This strong electromagnetic interference can be DC electromagnetic fields, continuous wave electromagnetic fields, modulated signal electromagnetic fields, pulsed electromagnetic fields, etc. The threshold field strength at which sensitive equipment can withstand a certain type of electromagnetic interference in an unshielded environment is E. s If the unit of measurement is dBV / m, then the shielding attenuation of this type of electromagnetic interference by the shielded room is A. p The dimension is dB. The "such electromagnetic interference" mentioned above includes, but is not limited to, electromagnetic interference from DC electromagnetic fields, continuous wave electromagnetic fields, modulated signal electromagnetic fields, pulsed electromagnetic fields, etc. Let's assume that the interference field strength generated by this electromagnetic interference at a location outside the shielded room immediately adjacent to the shielded room is E. out If the unit of measurement is dBV / m, then the shielding attenuation A p The requirements are:

[0088] A p [dB] = E out [dBV / m]-E s [dBV / m] (7)

[0089] Among them, E s The threshold field strength for a sensitive device to withstand a certain electromagnetic interference in an unshielded environment, measured in dBV / m, is obtained through actual measurement or the equipment's design specifications; E out This refers to the interference field strength generated by this type of strong electromagnetic interference at a location immediately adjacent to the shielding room outside the shielding room. The unit of measurement is dBV / m, and this value is obtained through measurement or evaluation simulation; such as A calculated based on equation (7). p If the value is less than or equal to 0dB, then no shielding is required.

[0090] V. Calculating the required reflection level in the quiet zone of an anechoic chamber based on antenna pattern measurement uncertainty

[0091] Quiet zone reflection level is an important source of uncertainty in antenna pattern parameter measurement. Here, we propose its uncertainty mathematical model and quantitative relationship.

[0092] The method for calculating the voltage amplitude ratio under the most stringent conditions. The far-field quiet zone reflection level of the antenna is a relative level value defined in the gain direction on the front of the antenna, such as... Figure 3 As shown, under the most severe conditions, The electric field vector representing the direct wave acts on the angular region of the antenna pattern that has relatively low directivity, such as nulls and back lobes. The electric field vector representing the reflected wave acts on the direction of maximum gain of the antenna in the analysis. In the normalized radiation pattern, the maximum gain is obviously 0 dB. Assume the expected value of a certain antenna parameter being measured is A. s dB, obviously A s It is a negative number, assuming the quiet zone reflection level is QdB. Then, the ratio of the voltage amplitude of the reflected wave to the direct wave formed at the antenna receiving port can be called the reflection-to-direct-wave ratio, which is:

[0093] RDR[dB]=QA s (8)

[0094] The linear dimensionless form of the amplitude of the direct reflection ratio is M RDR :

[0095]

[0096] Due to the presence of reflected waves, the actual received signal differs from the ideal situation. Assuming the ideal received signal voltage vector is 1, then the voltage vector of the received signal with reflected waves is:

[0097]

[0098] Voltage phase of the reflected wave It is a random quantity, which can be considered to be uniformly distributed in the range of 0 to 360°. The geometric meaning of equation (10) is as a vector on the complex plane. Figure 4 As shown.

[0099] Therefore, the error in the actual power measurement is obviously:

[0100]

[0101] Clearly, the probability distribution curve of this error contribution is not symmetric about the y-axis, because... Figure 4 It can be seen that the maximum and minimum values ​​of its error are E r-max and E r-min :

[0102] E r-max =20lg|1+M RDR | (12)

[0103] E r-min =20lg|1-M RDR | (13)

[0104] Obviously:

[0105] E r-max ≠-E r-min (14)

[0106] Mathematically, it can be proven that when the reflected direct light ratio (RDR) is small, for example, less than -20 dB, M RDR If it is less than 0.1, then:

[0107] E r-max ≈-E r-min (15)

[0108] In many uncertainty calculations in practical engineering, the mathematical condition that RDR is less than -20dB may not be strictly met. We can consider the following and analyze its absolute value:

[0109] |E r-min |>|E r-max | (16)

[0110] To be on the safe side, we can take the standard uncertainty component U introduced by reflection. R for:

[0111]

[0112] Where k is the expansion factor, which is empirically set to 2 or 3; calculate the standard uncertainty component introduced by reflection under different reflection direct ratios according to equation (17). Then, calculate the mapping relationship and mapping curve between the quiet zone reflection level and the standard uncertainty of the antenna pattern according to this process, and then find the required quiet zone reflection level index based on the desired standard uncertainty.

[0113] VI. Calculation of the contribution of the taper index in the quiet zone of the anechoic chamber to the uncertainty of radiation pattern measurement

[0114] When the antenna under test is within the quiet zone, assume that the taper parameter corresponding to the furthest distance the antenna deviates from the center of the quiet zone is T. a If the dimension is dB, then for safety, the uncertainty component of the pattern measurement introduced by the taper is u. T [dB] is obtained through simulation or measurement.

[0115] Example 1

[0116] The method described in steps S1-S3 is illustrated using the NB-IoT module receiver sensitivity test item. Figure 2 The test setup is shown. The antenna is a 0.8GHz–50GHz ultra-wideband omnidirectional antenna. The spectrum analyzer operates in the NB-IoT receiving band. With appropriate channel bandwidth settings, multiple measurements were taken to obtain I = -88dBm. Referring to the technical specifications of the NB-IoT module under test, P = -120dBm was chosen. Considering the accuracy requirements of the test, u can be used. I =0.5dB, then substituting into equation (3) yields the shielding attenuation requirement A. I =41dB.

[0117] Example 2

[0118] This method is illustrated using the TD-LTE mobile terminal receiver sensitivity test. The spectrum analyzer operates in the TD-LTE receive band. With an appropriate channel bandwidth setting, multiple measurements were taken to obtain I = -72dBm. Referring to the technical specifications of the TD-LTE terminal under test, P = -115dBm was chosen. Considering the accuracy requirements of the test, u can be selected as... I =0.5dB, then substituting into equation (3) yields the shielding attenuation requirement A = 52dB.

[0119] Equation (6) can also be used for evaluation. For rigorous evaluation, bandwidth B can be taken as the lower bandwidth of 1.4MHz in the typical TD-LTE system configuration. N =0.4dB, substituting into equation (6) for evaluation, the shielding attenuation requirement A is calculated. N =51dB.

[0120] Examples 1 and 2 illustrate that in radio frequency (RF) test projects requiring shielding, there is no universally applicable fixed value for shielding attenuation requirements. These requirements need to be calculated for specific test projects, and this calculation depends on the actual interference signal level under the measurement conditions. This patent proposes a method for evaluating interference signal levels through measurement, supplemented by information such as the noise floor bandwidth of the transceiver system. The required shielding attenuation can be quantitatively calculated using equations. For the purpose of prudent evaluation, the method proposed in this paper is relatively stringent; the calculated shielding attenuation requirement already includes a margin, as explained in the text. Experimental examples of NB-IoT module receiver sensitivity testing and LTE mobile terminal receiver sensitivity testing demonstrate that this evaluation calculation method is clear and feasible.

[0121] Example 3

[0122] Calculate the parameters of the reflected wave in the anechoic chamber, including the voltage phase of the reflected wave. Since it is a random quantity, it can be assumed to be uniformly distributed within the range of 0 to 360°. Then, the probability density curves of the two-sample errors can be obtained through numerical calculation, such as... Figure 5 , Figure 6 As shown. Figure 5 The curve is an example of equation (8). At this time, the probability distribution of its error is approximately a U-shaped distribution, and an expansion factor can be taken. This model is similar to the receiving power measurement error model caused by impedance mismatch. Therefore, we obtain... Figure 7 The effect of the direct reflection ratio on the standard uncertainty component is shown.

[0123] Example 4

[0124] Based on typical values ​​in industry standards, the front-to-back ratio is taken as 25dB (corresponding to the expected value of the measured pattern parameter -25dB), and the sidelobe relative level is taken as -17dB. Two calculation examples are given respectively. Figure 8 , Figure 9 As shown.

[0125] In practical uncertainty engineering calculations, the design value of the antenna pattern or the measured value can be used as the "expected value of the parameter". Generally, the "uncertainty of the uncertainty component" caused by this is within an acceptable range.

[0126] from Figure 8 and Figure 9 The calculation results show that when the expected value of the measured pattern parameter is low, the uncertainty component introduced by the quiet zone reflection level is relatively large. These parameters include front-to-back ratio, top lobe level suppression, cross-polarization ratio, and zero-fill. The higher the quiet zone reflection level, the more significant its contribution to the measurement error of the pattern parameters.

[0127] While several embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to these embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A method for determining parameters of an anechoic chamber, the anechoic chamber comprising a shielded area and a quiet area, characterized in that, The method includes: S1. Measure the value of the interference signal level I under unshielded conditions; S2. Determine the pre-received signal level P, and the uncertainty component of the magnitude of P due to co-channel interference; S3. Based on the results of steps S1 and S2, calculate the shielding attenuation requirement A of the shielded room based on the signal-to-interference ratio I； Assume the expected minimum signal level to be received in the RF test is P, the interference signal level in the unshielded condition is I, and the shielding attenuation of the shielded chamber in the interference signal frequency band is A. I The signal-to-interference ratio (SIR) during testing in a shielded room is: (1)； Co-channel interference introduces an uncertainty component into the value of P, which is evaluated using equation (2): (2) Combining equations (1) and (2), we can obtain: (3) ； In the pre-received signal levels P, u I Given that the demand is difficult to estimate, the shielding attenuation requirement A for the shielded room is calculated based on the increase in background noise. N : The known noise floor of the radio frequency signal is: (4) Where F is the equivalent linear value of the signal-to-noise figure, which is taken as 1, and K is the Boltzmann constant, which is taken as 1.38 × 10⁻⁶. -23 B is the signal bandwidth, and T is the thermodynamic temperature, taken as 290 Kelvin at room temperature. After the introduction of external interference, the equivalent noise floor increases. Let the allowable increase limit be u. N ; (5) Combining equation (4), we get: (6) 。 2. The method for determining the parameters of an anechoic chamber as described in claim 1, characterized in that, In step S3, if it is necessary to use the values ​​of these three shielding attenuation requirements or two of them simultaneously in actual engineering, the maximum value shall be taken.

3. The method for determining the parameters of an anechoic chamber as described in claim 1, characterized in that, In step S2, the pre-received signal level P and the uncertainty component of the magnitude of P due to co-channel interference are obtained through test standards or measurement practice.

4. The method for determining the parameters of an anechoic chamber as described in claim 1, characterized in that, In step S1, the value of the interference signal level I under unshielded conditions is obtained using the following method: Under unshielded conditions, the spectrum analyzer is connected to the receiving antenna via a cable. The cable is the same as that used in the actual test in the shielded room. An omnidirectional antenna is selected for the receiving antenna. The spectrum analyzer is set to the frequency band and bandwidth corresponding to the test item. The channel power function is used to measure the interference signal level. Measure 5 to 20 times under different time, location, and antenna polarization direction conditions, and take the maximum value.

5. The method for determining the parameters of an anechoic chamber as described in claim 1, characterized in that, In step S2, the method further includes calculating the shielding attenuation requirement A for strong electromagnetic interference. p The co-channel interference is strong electromagnetic interference outside the shielded room. In this case, the shielding attenuation requirement A of the shielded room for this type of strong electromagnetic interference is... p for: ； Among them, E s The threshold field strength for a sensitive device to withstand a certain electromagnetic interference in an unshielded environment, measured in dBV / m; E out This refers to the interference field strength generated by this type of strong electromagnetic interference at a location immediately adjacent to the shielded room outside the shielded room, with dimensions in dBV / m; if the calculated A p If the value is less than or equal to 0 dB, then no shielding is required.

6. The method for determining the parameters of an anechoic chamber as described in claim 5, characterized in that, The strong electromagnetic interference outside the shielded room includes DC electromagnetic fields, continuous wave electromagnetic fields, modulated signal electromagnetic fields, and pulse electromagnetic fields.

7. The method for determining the parameters of an anechoic chamber as described in claim 1, characterized in that, The anechoic chamber parameters also include the quiet zone reflection level. The quiet zone reflection level of the anechoic chamber is calculated based on the antenna pattern measurement uncertainty. The specific method is as follows: Suppose the expected value of a certain antenna parameter being measured is A. s dB, the quiet zone reflection level is QdB, and the ratio of the voltage amplitude of the reflected wave to the direct wave formed at the antenna receiving port is called the reflection-to-direct-wave ratio RDR: ； The linear dimensionless form of the amplitude of the direct reflection ratio (RDR) is M. RDR : ； Due to the presence of reflected waves, the actual received signal differs from the ideal situation. Assuming the ideal received signal voltage vector is 1, then the voltage vector of the received signal with reflected waves is: ； The voltage phase φ of the reflected wave is a random quantity that is uniformly distributed within the range of 0 to 360°. The error in the actual measured power is: ； The maximum and minimum values ​​of its error are E r-max and E r-min : The standard uncertainty component u introduced by reflection R for: ； Where k is the expansion factor; the standard uncertainty component u introduced by reflection is calculated under different direct reflection ratios. R The mapping relationship and mapping curve between the quiet zone reflection level and the standard uncertainty component of the antenna pattern are obtained, and the required quiet zone reflection level is found based on the desired standard uncertainty component.

8. The method for determining the parameters of an anechoic chamber as described in claim 7, characterized in that, When the antenna under test is within the quiet zone, assume that the taper parameter corresponding to the furthest distance the antenna deviates from the center of the quiet zone is T. a The dimension is dB; the uncertainty component of the pattern measurement introduced by the taper is u. T [dB] is obtained through simulation or measurement.

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