Some standard content:
Standard SJ2534.8-86 of the Ministry of Electronics Industry of the People's Republic of China
Antenna Test Method
Phase Measurement
Published on January 24, 1986
Implemented on October 1, 1986
Approved by the Ministry of Electronics Industry of the People's Republic of China Standard Antenna Test Method of the Ministry of Electronics Industry of the People's Republic of China
Phase Measurement
This standard applies to the phase measurement of antennas. 1 Overview
SJ 2534.8-86
Generally, the amplitude and phase of the radiation field components of two specific orthogonal polarizations are used to fully describe the radiation pattern of the antenna. Since the phase characteristics of the antenna radiation field contain very important information, phase measurement is particularly important in some occasions. 1.1 Occasions using the phase characteristics of the radiation field
1.1.1 Far field situation
The occasions where necessary information needs to be extracted from the far field phase change are: a. Determine the focusing of the focusing reflector; b. Self-tracking antenna;
e. Phase interferometer.
1.1.2 Near field situation
In the near field situation, the phase characteristics are used to: accurately predict the far field pattern based on the phase and amplitude changes in the near field, b. In other cases, it is used to describe the characteristics of an antenna. 1.2 Definition of phase
1.2.1 Phase of scalar field
The change of a single-frequency field component with angular frequency @ over time can be expressed by the following formula: e(t)=E. cog(ot+)=Re(EejwejotyWhere:
—real number
E. Positive real number.
The phase of e(t) at time t is the phase angle of the complex number E..(\+ot), that is, the phase e(t)=±+t
When the time is not specified, the phase of e(t) refers to the phase at t=0, that is, the phase=
1.2.1.1 Phase lag
If the field e propagates along the x-axis at a speed of v=/k, then e(t,x)=E.cos(ot-kx+y)
Where: k—wave number.
Issued by the Ministry of Electronics Industry on July 24, 1986
（1）
（4）
Implemented on October 1, 1986
SJ 2534.8-86
The change of the field at point t can be represented by the displacement of the curve (t, 0) in the positive direction ×/v (see Figure 1). This is called phase lag (or delay, lag). The field is transmitted from x=0 to sx
Figure 1 Phase shift of a single-frequency field propagating along the direction 1.2.2 Phase of the vector field
1.2.2.1 Phase of the linearly polarized field vector
The linearly polarized field vector can be expressed as the product of a scalar function (t) and a unit vector u representing the polarization direction, that is, E(t)e(t)u| The phase of |tt||8(t) is the phase angle of E. J. (5)
1.2.2.2 Phase of elliptically polarized field vector
In the case of elliptically polarized field vector; the field can still be expressed by equation (5), but u is a complex vector with an amplitude of 1 (uu=1). The vector u is not only uniquely specified by the polarization and normalization conditions, but can also be replaced by u\=uela, where u\ represents a vector with the same polarization as u but a phase difference of α. This changes accordingly, so u should be specified according to a clear convention.
2 Phase direction diagram
The specified component of the antenna radiation field can be expressed by the following formula: j(0,o)-jkr
Eu(t,e,$)F(0.Φ)e
where F and W represent the relationship between the amplitude and phase of the specified component and (9,), respectively, and (r,,) is the spherical coordinate of the observation point.
2.1 Linear polarization case
As described in 1.2.2.1, for linear polarization, u is a real vector (such as adding unit quantities ue and u in the and directions). Therefore, (0,) is uniquely determined, and (0,) is called the phase pattern . 2.2 Circular and circular polarization cases
For circular or elliptical polarization, as described in 1.2.2.2, when discussing the phase pattern, for each direction of interest (9, in), 2
u should be specified by explicit convention.
3 Phase center of the antenna
SJ2534.8-86
In many applications, it is necessary to specify a special reference point for the antenna, from which the radiation is considered to be emitted. This reference point is called the phase center, the apparent phase center and the center of curvature, depending on the definition. 3.1 Phase center
For any given frequency, if there is a coordinate origin such that the (°, in) in equation (6) is independent of and in, then this origin is called the phase center of the spherical wavefront or the equiphase plane. In this case, for a specified polarization, the real function F (, in) can be used to describe the pattern.
3.1.1 Phase Center Example
For even or odd cross-symmetric linear antennas or antenna arrays, if the current satisfies the following condition: 1(-x) = ±I'(x) ...
In this case, a phase center exists.
3.2 Apparent Phase Center
For most practical antennas, there is no "true" phase center that is valid in all directions. In this case, the concept of apparent phase center can be used. If, when referenced to a certain point, (9,) is approximately constant within the angular range of interest (e.g., a portion of the antenna main beam), then this point is called the apparent phase center. 3.3 Center of Curvature
The theoretical calculation of the apparent phase center is very cumbersome and is limited to antennas for which the complete expression of the far field is known. In this case, the most direct approach is to calculate the center of curvature of the isophase surface at the point of interest. There are generally two principal centers of curvature in each normal direction of the isophase surface.
3.4. The significance of phase center in antenna design Determining the location of the radiation reference point, i.e., the phase center, is crucial and sometimes a prerequisite for the successful design of the primary feed antenna of phased array and reflector antennas. In addition, when designing the tracking and navigation system of space vehicles and the rendezvous radar, it is also necessary to accurately determine the phase characteristics and phase reference points of each unit in these systems. 4 Phase measurement
4.1 Overview
4.1.1: Reference signal setting method
Since the phase is a relative quantity (due to the periodic nature of the angle, the phase value is limited to within 2 radians), a reference signal must be provided for comparison. There are three methods for setting the reference signal. 4.1.1.1 Close-range measurement
The block diagram is shown in Figure 2(a). The antenna under test is used as the transmitting antenna. A simple receiving antenna or detector is used to sample the radiation field. The reference signal is coupled out from the transmission line leading to the antenna under test and compared with the received signal in an appropriate circuit.
4.1.1.2 Long-distance measurement
The block diagram is shown in Figure 2 (b). The signal from the long distance is received by the antenna under test and the fixed reference antenna at the same time, and the sampled signal and the reference signal are directly compared. When measuring the phase pattern, the antenna under test is rotated in the usual way to measure the amplitude pattern.
Signal source
Phase measurement
Phase measurement
Antenna under test
Moveable tester
Reference branch
Test branch
Fixed antenna
Test branch Rotating joint
Flexible cable
Long-distance signal source
Antenna under test
Figure 2 Equipment for measuring phase pattern
(a) Near field (or close distance), phase pattern 4.1.1.3 Relative phase shift measurement of multi-port antenna
(b) Far field phase pattern
The block diagram is shown in Figure 3. With one branch of the multi-port antenna as the reference branch, the test branch is connected to the rest of the ports of the multi-port antenna in turn, and the relative phase between the two ports of the multi-port antenna can be measured. The relative phase is a function of the rotation angle of the antenna. 4.1.2 Determination of Phase Center from Measured Phase Pattern In many applications, it is necessary to determine or verify the position of the phase center of an antenna under development or manufacture by experimental methods. The typical characteristics of the phase pattern of an antenna with a fairly clear phase center are studied below. This is helpful for interpreting the radiation pattern of an antenna with unknown characteristics.
Reference branch
Phase measurement
Measurement branch
Rotation joint
Measured antenna
Remote signal source
Figure 3 Position measurement between two ports of a multi-port antenna Assume that the antenna is located in the (r, e,) coordinate system, and +0° is the antenna axis. It is assumed that the antenna has a phase center on the structural axis. When measuring the phase pattern, the antenna rotates around the rotation center. 4.1.2.1 The phase center coincides with the rotation center. By definition, the phase is constant in the main beam. If the amplitude pattern has side lobes, a phase reversal of 4
SJ2534.8-86
180° occurs at each zero value, and the phase pattern will show a sudden change. 4.1.2.2 The phase center is axially offset from the rotation center. If the phase center of the antenna is axially offset from the rotation center, the offset is 1. When is much smaller than the distance from the antenna to the observation point, and the phase pattern is normalized relative to the received signal at position A in Figure 4 (a), then for an antenna with only one beam, its integrated phase pattern is given by the following formula: Rotation center
Phase center
Figure 4 Geometry and phase change when the displacement signal source rotates around a given origin rkr/(1-cos0)
If the phase pattern is normalized relative to the signal received at position B in Figure 4 (b), the mirror image of the pattern in Figure 4 (a) is obtained.
4.1.2.2.1 Phase center from the phase pattern The position of the phase center can be calculated theoretically based on the phase pattern measured in 4.1.2.2. If the measured phase change when the antenna rotates from 8=0° to 9=e, then the displacement between the phase center and the rotation center is: (9)
However, due to the abnormality of the phase pattern and the experiment, it may be necessary to actually displace the antenna along its axis by several distances and record the phase pattern to include the case of r=0. Another very useful case is to find the position of the apparent phase center in the radiation near field based on the phase pattern measured in the radiation near field:
R(1-cos0)
Where: R. The distance from the rotation center to the observation point. coso
4.1.2.3 The phase center has axial and lateral displacements with respect to the rotation center (10)
As shown in Figure 4(c). (d), if the phase center has axial and lateral displacements with respect to the rotation center, the displacements are r and d respectively, then the phase change when rotating around the rotation center is: p~kr
where: r\)\=(r\)\+d\.
4.1.2.4 Methods to reduce the phase center measurement error (11)
If the minimum measurable phase change, i.e. the resolution of the phase discrimination system, is 0.5°, and the phase comparison is performed within the range of 1°=±10° from the antenna axis, then the uncertainty of the measured phase center may be as large as 0.1 wavelength. The following method can be used to reduce the phase center measurement error. If the antenna has a phase center within a larger angular range, then rmi can be measured within the required angular range, and then a second rmin can be measured within a larger angular range and/or a second rmin can be measured when the phase center approaches the rotation center from the opposite direction. Ideally, the phase center falls between the two values of rmin. 4.1.2.5 Requirements for the positioner
When the phase center is measured, the antenna under test is mounted on the positioner and is located in the far zone (or radiating near field zone) of the source with the required polarization. The antenna under test rotates precisely around a point on the positioner and can be precisely moved along the antenna axis. In order to correct and estimate the lateral displacement of the phase center from the axis, and to correct the mechanical error of the positioner, it is best to move the antenna precisely in the vertical direction of the axis.
4.2 Test equipment
Currently available equipment includes:
RF undervoltage voltmeter;
b: Computer-controlled and manually controlled RF network analyzer, c: Computer-controlled and manually controlled amplitude receiver, d. Phase meter.
If necessary, the phase measurement system can also be assembled according to actual needs. 4.3 Error sources
Whether using a phase measurement instrument or an assembled system, many error sources must be considered. 4.3.1. Errors introduced by reflections
In phase measurement, the interaction of reflected waves caused by the mismatch between components and the waveguide or transmission line used is one of the main sources of error6
SJ2534.8-86
. In addition to causing phase errors, these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line due to multiple reflections between components. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is approximately
sin-1/F.//T2/
（12）
where 厂1 and 厂 are the reflection coefficients of the two discontinuities viewed from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratio of the reading instrument or component connected to any two points on the transmission line is 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflection
The only way to reduce the reflection-induced error is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuation plate. However, the mismatch of the transmission line connector is difficult to reduce, so the effect of this method is limited. If possible, polished flanges and precision connectors should be used as much as possible. 4.3.2 Error introduced by frequency instability
When measuring the phase, the signal must be sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f1 to f2, the phase measurement error between the signals of the two paths is approximately: -1--12
where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f1 and f2. If the two paths consist of a waveguide or a combination of transmission line and free space, the electrical lengths must be calculated separately. To reduce this measurement error, an additional transmission line should be added to the shorter path to keep the electrical lengths of the two paths equal. This requirement is essential for swept frequency measurements.
4.3.2.1 Example of error introduced by frequency instability Assuming the measurement frequency is 1000 MHz and the free space path lengths between the two paths differ by 1 meter, the phase change between the two channels caused by a frequency change of 1 MHz (frequency stability of 0.1%) is 1.2°. 4.3.3 Error introduced by cable bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving probe in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods to reduce errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes where the meter must bend or fold, b. The cable used should be long enough to avoid sharp bending and excessive movement of the cable, e. Use cables with reduced loss, because cables with slightly higher losses will change their phase shift by 7% when bending or folding compared to cables with lower losses
SJ2534.8-86
&. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes
Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a spatial function.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement.
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, the details of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of, for example, 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard was Ke Shuren.2 Phase center and rotation center have axial offset If the phase center of the antenna is axially offset from the rotation center, the offset is 1. When is much smaller than the distance from the antenna to the observation point, and the phase pattern is normalized relative to the received signal at position A in Figure 4 (a), then for an antenna with only one beam, its integrated phase pattern is given by the following formula: Rotation center
Phase center
Figure 4 Geometry and phase change when the displacement signal source rotates around a given origin rkr/(1-cos0)
If the phase pattern is normalized relative to the signal received at position B in Figure 4 (b), the mirror image of the pattern in Figure 4 (a) is obtained.
4.1.2.2.1 Phase center of the phase pattern The phase center position can be theoretically calculated based on the phase pattern measured in 4.1.2.2. If the measured phase change when the antenna rotates from 8 = 0° to 9 = e, then the displacement between the phase center and the rotation center is: (9)
However, due to the phase pattern and experimental anomalies, it is actually necessary to displace the antenna along its axis by several distances and record the phase pattern to include the case of r = 0. Another very useful case is to find the position of the apparent phase center in the radiation near field based on the phase pattern measured in the radiation near field:
R(1-cos0)
Where: R. The distance from the rotation center to the observation point. coso
4.1.2.3 The phase center has axial and lateral displacements with respect to the rotation center (10)
As shown in Figure 4(c). (d), if the phase center has axial and lateral displacements with respect to the rotation center, the displacements are r and d respectively, then the phase change when rotating around the rotation center is: p~kr
where: r\)\=(r\)\+d\.
4.1.2.4 Methods to reduce the phase center measurement error (11)
If the minimum measurable phase change, i.e. the resolution of the phase discrimination system, is 0.5°, and the phase comparison is performed within the range of 1°=±10° from the antenna axis, then the uncertainty of the measured phase center may be as large as 0.1 wavelength. The following method can be used to reduce the phase center measurement error. If the antenna has a phase center within a larger angular range, then rmi can be measured within the required angular range, and then a second rmin can be measured within a larger angular range and/or a second rmin can be measured when the phase center approaches the rotation center from the opposite direction. Ideally, the phase center falls between the two values of rmin. 4.1.2.5 Requirements for the positioner
When the phase center is measured, the antenna under test is mounted on the positioner and is located in the far zone (or radiating near field zone) of the source with the required polarization. The antenna under test rotates precisely around a point on the positioner and can be precisely moved along the antenna axis. In order to correct and estimate the lateral displacement of the phase center from the axis, and to correct the mechanical error of the positioner, it is best to move the antenna precisely in the vertical direction of the axis.
4.2 Test equipment
Currently available equipment includes:
RF undervoltage voltmeter;
b: Computer-controlled and manually controlled RF network analyzer, c: Computer-controlled and manually controlled amplitude receiver, d. Phase meter.
If necessary, the phase measurement system can also be assembled according to actual needs. 4.3 Error sources
Whether using a phase measurement instrument or an assembled system, many error sources must be considered. 4.3.1. Errors introduced by reflections
In phase measurement, the interaction of reflected waves caused by the mismatch between components and the waveguide or transmission line used is one of the main sources of error6
SJ2534.8-86
. In addition to causing phase errors, these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line due to multiple reflections between components. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is approximately
sin-1/F.//T2/
（12）
where 厂1 and 厂 are the reflection coefficients of the two discontinuities viewed from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratio of the reading instrument or component connected to any two points on the transmission line is 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflection
The only way to reduce the reflection-induced error is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuation plate. However, the mismatch of the transmission line connector is difficult to reduce, so the effect of this method is limited. If possible, polished flanges and precision connectors should be used as much as possible. 4.3.2 Error introduced by frequency instability
When measuring the phase, the signal must be sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f1 to f2, the phase measurement error between the signals of the two paths is approximately: -1--12
where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f1 and f2. If the two paths consist of a waveguide or a combination of transmission line and free space, the electrical lengths must be calculated separately. To reduce this measurement error, an additional transmission line should be added to the shorter path to keep the electrical lengths of the two paths equal. This requirement is essential for swept frequency measurements.
4.3.2.1 Example of error introduced by frequency instability Assuming the measurement frequency is 1000 MHz and the free space path lengths between the two paths differ by 1 meter, the phase change between the two channels caused by a frequency change of 1 MHz (frequency stability of 0.1%) is 1.2°. 4.3.3 Error introduced by cable bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving probe in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods to reduce errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes where the meter must bend or fold, b. The cable used should be long enough to avoid sharp bending and excessive movement of the cable, e. Use cables with reduced loss, because cables with slightly higher losses will change their phase shift by 7% when bending or folding compared to cables with lower losses
SJ2534.8-86
&. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes
Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a spatial function.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement.
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, the details of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of, for example, 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard was Ke Shuren.2 Phase center and rotation center have axial offset If the phase center of the antenna is axially offset from the rotation center, the offset is 1. When is much smaller than the distance from the antenna to the observation point, and the phase pattern is normalized relative to the received signal at position A in Figure 4 (a), then for an antenna with only one beam, its integrated phase pattern is given by the following formula: Rotation center
Phase center
Figure 4 Geometry and phase change when the displacement signal source rotates around a given origin rkr/(1-cos0)
If the phase pattern is normalized relative to the signal received at position B in Figure 4 (b), the mirror image of the pattern in Figure 4 (a) is obtained.
4.1.2.2.1 Phase center of the phase pattern The phase center position can be theoretically calculated based on the phase pattern measured in 4.1.2.2. If the measured phase change when the antenna rotates from 8 = 0° to 9 = e, then the displacement between the phase center and the rotation center is: (9)
However, due to the phase pattern and experimental anomalies, it is actually necessary to displace the antenna along its axis by several distances and record the phase pattern to include the case of r = 0. Another very useful case is to find the position of the apparent phase center in the radiation near field based on the phase pattern measured in the radiation near field:
R(1-cos0)
Where: R. The distance from the rotation center to the observation point. coso
4.1.2.3 The phase center has axial and lateral displacements with respect to the rotation center (10)
As shown in Figure 4(c). (d), if the phase center has axial and lateral displacements with respect to the rotation center, the displacements are r and d respectively, then the phase change when rotating around the rotation center is: p~kr
where: r\)\=(r\)\+d\.
4.1.2.4 Methods to reduce the phase center measurement error (11)
If the minimum measurable phase change, i.e. the resolution of the phase discrimination system, is 0.5°, and the phase comparison is performed within the range of 1°=±10° from the antenna axis, then the uncertainty of the measured phase center may be as large as 0.1 wavelength. The following method can be used to reduce the phase center measurement error. If the antenna has a phase center within a larger angular range, then rmi can be measured within the required angular range, and then a second rmin can be measured within a larger angular range and/or a second rmin can be measured when the phase center approaches the rotation center from the opposite direction. Ideally, the phase center falls between the two values of rmin. 4.1.2.5 Requirements for the positioner
When the phase center is measured, the antenna under test is mounted on the positioner and is located in the far zone (or radiating near field zone) of the source with the required polarization. The antenna under test rotates precisely around a point on the positioner and can be precisely moved along the antenna axis. In order to correct and estimate the lateral displacement of the phase center from the axis, and to correct the mechanical error of the positioner, it is best to move the antenna precisely in the vertical direction of the axis.
4.2 Test equipment
Currently available equipment includes:
RF undervoltage voltmeter;
b: Computer-controlled and manually controlled RF network analyzer, c: Computer-controlled and manually controlled amplitude receiver, d. Phase meter.
If necessary, the phase measurement system can also be assembled according to actual needs. 4.3 Error sources
Whether using a phase measurement instrument or an assembled system, many error sources must be considered. 4.3.1. Errors introduced by reflections
In phase measurement, the interaction of reflected waves caused by the mismatch between components and the waveguide or transmission line used is one of the main sources of error6
SJ2534.8-86
. In addition to causing phase errors, these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line due to multiple reflections between components. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is approximately
sin-1/F.//T2/
（12）
where 厂1 and 厂 are the reflection coefficients of the two discontinuities viewed from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratio of the reading instrument or component connected to any two points on the transmission line is 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflection
The only way to reduce the reflection-induced error is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuation plate. However, the mismatch of the transmission line connector is difficult to reduce, so the effect of this method is limited. If possible, polished flanges and precision connectors should be used as much as possible. 4.3.2 Error introduced by frequency instability
When measuring the phase, the signal must be sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f1 to f2, the phase measurement error between the signals of the two paths is approximately: -1--12
where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f1 and f2. If the two paths consist of a waveguide or a combination of transmission line and free space, the electrical lengths must be calculated separately. To reduce this measurement error, an additional transmission line should be added to the shorter path to keep the electrical lengths of the two paths equal. This requirement is essential for swept frequency measurements.
4.3.2.1 Example of error introduced by frequency instability Assuming the measurement frequency is 1000 MHz and the free space path lengths between the two paths differ by 1 meter, the phase change between the two channels caused by a frequency change of 1 MHz (frequency stability of 0.1%) is 1.2°. 4.3.3 Error introduced by cable bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving probe in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods to reduce errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes where the meter must bend or fold, b. The cable used should be long enough to avoid sharp bending and excessive movement of the cable, e. Use cables with reduced loss, because cables with slightly higher losses will change their phase shift by 7% when bending or folding compared to cables with lower losses
SJ2534.8-86
&. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes
Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a spatial function.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement.
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, the details of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of, for example, 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard was Ke Shuren.8-86
Record the phase pattern so that the case of r=0 is included. Another very useful case is to find the position of the apparent phase center in the radiation near field region based on the phase pattern measured in the radiation near field region:
R(1-cos0)
Where: R. The distance from the rotation center to the observation point. coso
4.1.2.3 The phase center has axial and lateral displacements with respect to the rotation center (10)
As shown in Figure 4(c). (d), if the phase center has axial and lateral displacements with respect to the rotation center, the displacements are r and d respectively, then the phase change when rotating around the rotation center is: p~kr
Where: r\)\=(r\)\+d\.
4.1.2.4 Methods for reducing phase centre measurement errors (11)
If the minimum measurable phase change, i.e. the resolution of the phase discrimination system, is 0.5° and the phase comparison is performed within a range of θ = ±10° from the antenna axis, the uncertainty of the measured phase centre may be as large as 0.1 wavelength. The following method can be used to reduce the phase centre measurement error. If the antenna has a phase centre within a large angular range, then rmi can be measured within the required angular range, and then a second rmin can be measured within a larger angular range and/or a second rmin can be measured when the phase centre approaches the centre of rotation from the opposite direction. Ideally, the phase centre falls between the two values of rmin. 4.1.2.5 Requirements for positioners
When performing phase centre measurements, the antenna under test is mounted on a positioner and is located in the far field (or radiating near field) of a source with the required polarisation. The antenna under test is precisely rotated around a point on the positioner and can be precisely moved along the antenna axis. In order to correct and estimate the lateral displacement of the phase center from the axis, and to correct the mechanical error of the positioner, it is best to move the antenna accurately in the vertical direction of the axis.
4.2 Test equipment
The equipment currently available includes:
RF under-measurement voltmeter;
b: Computer-controlled and manually controlled RF network analyzer, c: Computer-controlled and manually controlled amplitude receiver, d. Phase meter.
If necessary, the phase measurement system can also be assembled according to actual needs. 4.3 Error sources
Whether using a phase measurement instrument or an assembled system, many error sources must be considered. 4.3.1. Error introduced by reflection
In phase measurement, the interaction of reflected waves caused by the mismatch between the component and the waveguide or transmission line used is one of the main error sources6
SJ2534.8-86
. In addition to causing phase errors, multiple reflections between these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is about
sin-1/F.//T2/
（12）
where 1 and 2 are the reflection coefficients of the two discontinuities from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratios of the reading instruments or components connected to any two points on the transmission line are 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflections
The only way to reduce reflection-induced errors is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuator. However, it is difficult to reduce the mismatch of the transmission line joints, so the effect of this method is limited. If possible, polished flanges and precision joints should be used as much as possible. 4.3.2 Errors introduced by frequency instability
When measuring the phase, the signal is sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f, to f, the phase measurement error between the signals of the two paths is approximately: -1--12
Where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f, and f,. If the two paths include a combination of waveguide or transmission line and free space, the electrical lengths must be calculated separately. In order to reduce this measurement error, an additional transmission line should be added to the shorter channel to keep the electrical lengths of the two channels equal. This requirement is necessary for swept frequency measurements.
4.3.2.1 Example of Error Introduced by Frequency Instability Assume that the measurement frequency is 1000MHz and the free space path length between the two channels differs by 1 meter, then the phase change between the two channels caused by a frequency change of 1MHz (frequency stability is 0.1%) is 1.2°. 4.3.3 Error Introduced by Cable Bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving detector in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods for Reducing Errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes in places where the meter must bend or fold, b. Use cables that are long enough to avoid sharp bending and excessive movement of the cable, e. Use loss-reducing cables, because cables with slightly higher losses will have a phase shift change of 7 when bending or turning compared to cables with lower losses. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a function of space.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement.
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, every detail of the system must be carefully considered. Only when all factors are taken into consideration can we achieve a measurement accuracy of 5° or less. Additional Notes:
This standard was jointly proposed by the Standardization Research Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard is Ke Shuren.8-86
Record the phase pattern so that the case of r=0 is included. Another very useful case is to find the position of the apparent phase center in the radiation near field region based on the phase pattern measured in the radiation near field region:
R(1-cos0)
Where: R. The distance from the rotation center to the observation point. coso
4.1.2.3 The phase center has axial and lateral displacements with respect to the rotation center (10)
As shown in Figure 4(c). (d), if the phase center has axial and lateral displacements with respect to the rotation center, the displacements are r and d respectively, then the phase change when rotating around the rotation center is: p~kr
Where: r\)\=(r\)\+d\.
4.1.2.4 Methods for reducing phase centre measurement errors (11)
If the minimum measurable phase change, i.e. the resolution of the phase discrimination system, is 0.5° and the phase comparison is performed within a range of θ = ±10° from the antenna axis, the uncertainty of the measured phase centre may be as large as 0.1 wavelength. The following method can be used to reduce the phase centre measurement error. If the antenna has a phase centre within a large angular range, then rmi can be measured within the required angular range, and then a second rmin can be measured within a larger angular range and/or a second rmin can be measured when the phase centre approaches the centre of rotation from the opposite direction. Ideally, the phase centre falls between the two values of rmin. 4.1.2.5 Requirements for positioners
When performing phase centre measurements, the antenna under test is mounted on a positioner and is located in the far field (or radiating near field) of a source with the required polarisation. The antenna under test is precisely rotated around a point on the positioner and can be precisely moved along the antenna axis. In order to correct and estimate the lateral displacement of the phase center from the axis, and to correct the mechanical error of the positioner, it is best to move the antenna accurately in the vertical direction of the axis.
4.2 Test equipment
The equipment currently available includes:
RF under-measurement voltmeter;
b: Computer-controlled and manually controlled RF network analyzer, c: Computer-controlled and manually controlled amplitude receiver, d. Phase meter.
If necessary, the phase measurement system can also be assembled according to actual needs. 4.3 Error sources
Whether using a phase measurement instrument or an assembled system, many error sources must be considered. 4.3.1. Error introduced by reflection
In phase measurement, the interaction of reflected waves caused by the mismatch between the component and the waveguide or transmission line used is one of the main error sources6
SJ2534.8-86
. In addition to causing phase errors, multiple reflections between these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is about
sin-1/F.//T2/
（12）
where 1 and 2 are the reflection coefficients of the two discontinuities from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratios of the reading instruments or components connected to any two points on the transmission line are 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflections
The only way to reduce reflection-induced errors is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuator. However, it is difficult to reduce the mismatch of the transmission line joints, so the effect of this method is limited. If possible, polished flanges and precision joints should be used as much as possible. 4.3.2 Errors introduced by frequency instability
When measuring the phase, the signal is sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f, to f, the phase measurement error between the signals of the two paths is approximately: -1--12
Where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f, and f,. If the two paths include a combination of waveguide or transmission line and free space, the electrical lengths must be calculated separately. In order to reduce this measurement error, an additional transmission line should be added to the shorter channel to keep the electrical lengths of the two channels equal. This requirement is necessary for swept frequency measurements.
4.3.2.1 Example of Error Introduced by Frequency Instability Assume that the measurement frequency is 1000MHz and the free space path length between the two channels differs by 1 meter, then the phase change between the two channels caused by a frequency change of 1MHz (frequency stability is 0.1%) is 1.2°. 4.3.3 Error Introduced by Cable Bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving detector in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods for Reducing Errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes in places where the meter must bend or fold, b. Use cables that are long enough to avoid sharp bending and excessive movement of the cable, e. Use loss-reducing cables, because cables with slightly higher losses will have a phase shift change of 7 when bending or turning compared to cables with lower losses. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a function of space.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement.
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, every detail of the system must be carefully considered. Only when all factors are taken into consideration can we achieve a measurement accuracy of 5° or less. Additional Notes:
This standard was jointly proposed by the Standardization Research Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard is Ke Shuren.3 Error sources
Whether using phase measurement instruments or assembled systems, many error sources must be considered. 4.3.1. Errors introduced by reflections
In phase measurement, the interaction of reflected waves caused by the mismatch between components and the waveguide or transmission line used is one of the main error sources6
SJ2534.8-86
. In addition to causing phase errors, these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line due to multiple reflections between components. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is about
sin-1/F.//T2/
（12）
where 厂1 and 厂 are the reflection coefficients of the two discontinuities viewed from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratio of the reading instrument or component connected to any two points on the transmission line is 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflection
The only way to reduce the reflection-induced error is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuation plate. However, the mismatch of the transmission line connector is difficult to reduce, so the effect of this method is limited. If possible, polished flanges and precision connectors should be used as much as possible. 4.3.2 Error introduced by frequency instability
When measuring the phase, the signal must be sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f1 to f2, the phase measurement error between the signals of the two paths is approximately: -1--12
where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f1 and f2. If the two paths consist of a waveguide or a combination of transmission line and free space, the electrical lengths must be calculated separately. To reduce this measurement error, an additional transmission line should be added to the shorter path to keep the electrical lengths of the two paths equal. This requirement is essential for swept frequency measurements.
4.3.2.1 Example of error introduced by frequency instability Assuming the measurement frequency is 1000 MHz and the free space path lengths between the two paths differ by 1 meter, the phase change between the two channels caused by a frequency change of 1 MHz (frequency stability of 0.1%) is 1.2°. 4.3.3 Error introduced by cable bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving probe in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods to reduce errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes where the meter must bend or fold, b. The cable used should be long enough to avoid sharp bending and excessive movement of the cable, e. Use cables with reduced loss, because cables with slightly higher losses will change their phase shift by 7% when bending or folding compared to cables with lower losses
SJ2534.8-86
&. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes
Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a spatial function.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement. wwW.bzxz.Net
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, the details of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of, for example, 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard was Ke Shuren.3 Error sources
Whether using phase measurement instruments or assembled systems, many error sources must be considered. 4.3.1. Errors introduced by reflections
In phase measurement, the interaction of reflected waves caused by the mismatch between components and the waveguide or transmission line used is one of the main error sources6
SJ2534.8-86
. In addition to causing phase errors, these non-ideal components will also change the relative amplitude and phase of the traveling waves on the transmission line due to multiple reflections between components. The relative phase and amplitude of the wavefront in the mismatched case may be consistent with the relative phase and amplitude in the matched case, but most of them are between the two extreme cases caused by the mismatch. The maximum possible phase mismatch error caused by two cascaded discontinuities is about
sin-1/F.//T2/
（12）
where 厂1 and 厂 are the reflection coefficients of the two discontinuities viewed from a common point between the two discontinuities. 4.3.1.1 Example of reflection-induced error
Assume that the voltage standing wave ratio of the reading instrument or component connected to any two points on the transmission line is 1.3 and 1.5 respectively, then the relative phase between the fields at these two points may differ by ±1.49° from the case without reflection. 4.3.1.2 Methods to reduce reflection
The only way to reduce the reflection-induced error is to reduce the mismatch value of the reflection source. This is usually achieved with a well-matched attenuator or attenuation plate. However, the mismatch of the transmission line connector is difficult to reduce, so the effect of this method is limited. If possible, polished flanges and precision connectors should be used as much as possible. 4.3.2 Error introduced by frequency instability
When measuring the phase, the signal must be sent to the phase measurement system through two paths, so strict requirements must be placed on the frequency stability of the signal source. If the electrical lengths of the two paths are not exactly equal, then when the operating frequency shifts from f1 to f2, the phase measurement error between the signals of the two paths is approximately: -1--12
where 1, and, are the lengths of the two paths, and λ, and λ, are the waveguide wavelengths at f1 and f2. If the two paths consist of a waveguide or a combination of transmission line and free space, the electrical lengths must be calculated separately. To reduce this measurement error, an additional transmission line should be added to the shorter path to keep the electrical lengths of the two paths equal. This requirement is essential for swept frequency measurements.
4.3.2.1 Example of error introduced by frequency instability Assuming the measurement frequency is 1000 MHz and the free space path lengths between the two paths differ by 1 meter, the phase change between the two channels caused by a frequency change of 1 MHz (frequency stability of 0.1%) is 1.2°. 4.3.3 Error introduced by cable bending
In many measurements, such as the field measurement around an antenna, it is necessary to move the receiving probe in the air. When moving, the coaxial cable connected to the detector must be bent or folded, or several rotary joints must be rotated where waveguides are used. Most rotary joints change the phase of the output signal by several degrees when rotating. At microwave frequencies, when a short coaxial cable is bent or folded, its electrical length will change by 1 degree or several degrees. 4.3.3.1 Methods to reduce errors
The following methods can be used to reduce errors:
. Use cables with smaller phase shift changes where the meter must bend or fold, b. The cable used should be long enough to avoid sharp bending and excessive movement of the cable, e. Use cables with reduced loss, because cables with slightly higher losses will change their phase shift by 7% when bending or folding compared to cables with lower losses
SJ2534.8-86
&. Calibrate the phase shift when the rotary joint rotates. It should be noted that even for the same cable segment, different segments will have different phase shift changes when turning, so they should be carefully selected. 4.3.4 Errors introduced by temperature changes
Temperature changes will also cause errors. This change in electrical length is manifested as a measurement error of the phase change of the field as a spatial function.
4.3.5 Errors introduced by noise
A factor that is easily overlooked is the signal-to-noise ratio of the system. In order to prevent the influence of noise on the phase measurement error, a high signal-to-noise ratio must be achieved during measurement.
4.4 Measurement accuracy
As mentioned in 4.3, there are many sources of error in phase measurement. When making accurate measurements, the details of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of, for example, 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard was Ke Shuren.As mentioned in 3, there are many sources of error in phase measurement. When making accurate measurements, every detail of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Research Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard is Ke Shuren.As mentioned in 3, there are many sources of error in phase measurement. When making accurate measurements, every detail of the system must be carefully considered. Only when all factors are taken into account can a measurement accuracy of 5° or less be achieved. Additional notes:
This standard was jointly proposed by the Standardization Research Institute of the Ministry of Electronics and the 39th Institute. This standard was drafted by the 39th Institute of the Ministry of Electronics. The main drafter of this standard is Ke Shuren.
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