Some standard content:
Standard SJ2534.1-84 of the Ministry of Electronics Industry of the People's Republic of China
Antenna test method
Test equipment for antenna test field
Published on November 1, 1984
Ministry of Electronics Industry of the People's Republic of China
Implemented on July 1, 1985
Standard Antenna Test Method of the Ministry of Electronics Industry of the People's Republic of China
Test equipment for antenna test field
SJ2534.1-84
This standard applies to various test equipment for antenna test field for testing antenna performance. These equipment must be periodically measured by the accredited unit (the measurement period is generally one to three years) and kept and maintained regularly by a dedicated person. 1 Test equipment
1.1 The test equipment of a typical antenna test field can be divided into the following five subsystems: a. Source antenna system;
b. Transmitting system;
c. Receiving system;bzxZ.net
d. Positioning system:
e recording and data processing system.
The specific content of the test equipment required depends on the measurement requirements to be performed. For example, the test equipment can be a simple system that only measures the main plane radiation pattern of a simple antenna, or it can be a highly automated system that measures the complete characteristics of the antenna.
1.2 Antenna test field The block diagram of a typical test system is shown in Figure 1. 1.3 For complex measurements, the control unit, indicator, receiving system, recording and data processing system, and the tuning controller of the transmitting signal source are generally placed in the main control room. 1.4 For simpler measurements, appropriate covering can be made based on the principle of convenience for the operator. Issued by the Ministry of Electronics Industry of the People's Republic of China on November 1, 1984 and implemented on July 1, 1985
Receiver
Test antenna
Test positioner
Fixer
Recording equipment
SJ2534.1-84
Polarization locator
Source antenna
Test variable
Terminal indicator
Source tower indicator
Source tower control
?Signal source
Source control
Figure 1 Block diagram of a typical antenna test system
1.5 The signal source is usually placed on or near a remote antenna tower and connected to the source antenna through an appropriate feeder system.
2 Source antennas for antenna test sites
2.1 General requirements
Antenna test sites are generally designed to work over a wide frequency band, so the antenna test site should be equipped with a set of source antennas covering all used frequency bands. The beam width and polarization characteristics of the source antenna should be adapted to the measurements to be performed. 2.2 Form of source antenna
For frequencies below 1.0 GHz, the source antenna often uses a Yagi antenna, a helical antenna, or a logarithmic periodic antenna. For frequencies above 400 MHz, the source antenna often uses a parabolic series with a wide-band feed. In some cases, various horn antennas can also be used.
2.3 Means of controlling polarization
A linearly polarized antenna is installed on the polarization positioner so that the polarization direction of the source antenna can be rotated continuously. In order to ensure that the polarization state of the test antenna is correctly measured, it must be ensured that other properties of the source antenna do not change significantly during rotation. 2.4 Polarization conversion of circularly polarized source antenna
Circularly polarized source antenna should be designed to generate right-handed or left-handed circular polarization and orthogonal linear polarization through electrical or mechanical conversion. The polarization performance of circularly polarized antenna must be identified. 2.5 Polarization purity of linearly polarized source antenna
The polarization purity of linearly polarized source antenna is guaranteed by correct design and fine processing. 2.6 Standard gain antenna
SJ2534.1-84
When using the gain transfer method to measure power gain, a corresponding standard gain antenna must be equipped. The standard gain antenna should be pre-measured to reduce the error of gain measurement. 3 Transmitting system
3.1 Composition of the transmitting system
The transmitting system includes the transmitting signal source, the corresponding power amplifier and other related devices such as isolators, attenuators, conversion connectors, etc.). The specific content is determined by the overall measurement requirements. 3.2 Signal source form
The signal source forms mainly include triode cavity oscillators, klystrons, magnetrons and backward wave tube oscillators and various solid-state oscillators.
Generally, the performance requirements for signal sources are as follows: 3.2.1 Frequency control
The frequency control of the signal source can be mechanical, electrical-mechanical or electrical tuning. If the transmitting signal source is placed far away, a calibrated position servo loop or speed servo loop can be used to remotely tune the motor of the oscillator mechanically. For electrically tuned oscillators, an adjustable regulated power supply is required. 3.2.2 Frequency accuracy
The accuracy of the frequency indication mechanism of a general signal source is about 1%. When making precise measurements, a cavity wavelength meter, heterodyne frequency meter or digital frequency meter must be used to calibrate the frequency of the signal source. The oscillation frequency of some types of signal sources varies with coupling and load conditions, and sufficient attention should be paid to them during measurement. 3.2.3 Frequency stability
Since the antenna and its related RF circuits are very sensitive to frequency, the frequency of the signal source must remain relatively stable throughout the measurement process.
3.2.3.1General measurements require a frequency change of 10-\ to 10- within 30 minutes. Precision measurements (such as precision phase measurements) require a frequency stability of 10- or higher. 3.2.3.2 Common frequency stabilization methods include:
a, control the working environment (such as immersing the oscillator in a constant temperature bath). b, couple the oscillator to a high-quality Q cavity. Pound system - use an electrical method to make the oscillator reference a microwave cavity. c
d, automatic frequency control - use an electrical method to make the oscillator's frequency reference a stable source. Automatic phase control - phase lock the oscillator's frequency with a stable source. e
Select the frequency stabilization method based on the type of oscillator used and the requirements for frequency stability. 3.3 Spectral purity
Some types of oscillators have large harmonics, which will interfere with the desired signal when emitted. Therefore, a signal source with high spectral purity should be selected or a filter and a receiving system that can distinguish useful and useless signals should be used. 3.4 Power level
3.4.1 The power level required for measurement is determined by the gain of the source antenna and the antenna under test, the sensitivity of the receiver, the transmission attenuation between the two antennas and the dynamic range of the measurement. 3.4.2 The output power of the signal source is usually 0dBm to 33dBm. If it does not meet the test requirements, a corresponding power amplifier can be added.
3.4.3 The sensitivity of the typical detector used in antenna measurement is -50dBm to -65dBm. The sensitivity of the general receiver is -90dBm to -125dBm. Different choices can be made according to different requirements. 3.4.4 The output of the signal source is required to be relatively stable during measurement. Most short-term point frequency measurements expect the output to change no more than ±0.1 dB. For measurements such as insertion loss or gain transfer, only ±0.01 to ±0.05 dB is allowed to change in a short period of time. At this time, automatic level control (amplitude stabilization) is required. If necessary, power monitoring equipment can be added. 3.5 Modulation
Some measurement systems require frequency modulation. For example, the detector-measurement amplifier system used for simple measurements often requires the signal source to have an internal square wave modulation of 1000 Hz. The modulation frequency should have a certain modulation range and relative stability. Some occasions require special shaped pulses to reduce the distortion of the pulse spectrum. Therefore, the signal source should have various internal and external modulation functions according to requirements.
4 Receiving system
4.1 The simplest receiving system in the antenna amplitude pattern measurement system is a crystal detector or a bolometer detector (which is usually directly connected to the antenna under test or inside a scaled model) and its connected amplifier. The output of the amplifier is provided by an indicating instrument to provide readings for the tester or signals for the recorder. The signal source used should be square wave modulated within 1000Hz. The dynamic range of the system is limited by the square law characteristics of the detector and the linear range of the amplifier (referring to the direct recording method).
4.1.1 The dynamic range of the bolometer is about 40dB. For crystal detectors, when the audio load impedance is appropriate, it is about 35dB. The optimal audio load impedance of the crystal detector is about 2~6k2. 4.1.2 The detector made of reverse diode has a square law characteristic range of 50dB with high accuracy and good temperature stability when the audio load impedance is 2002. 4.1.3 Compensation means to widen the square law range of the detector: 4.1.3.1 An auxiliary potentiometer connected to the stylus drive mechanism is used to introduce a bias voltage in the measuring amplifier to change its gain. This bias voltage can be controlled so that the amplifier gain increases when the stylus moves to the lower scale. With a suitable adjustment mechanism, the dynamic range of this method can be increased to about 60 dB. 4.1.3.2 Another compensation method is to use a logarithmic amplifier, and the record is expressed in decibels. The slope of each stage of the logarithmic amplifier is adjusted according to different input levels so that the square law characteristic is satisfied over a wide range. This method can increase the dynamic range to about 60 dB.
4.1.4 The dynamic range of a simple detector-amplifier system is small and the test error is large. Typical data is an error of about ±1 dB in a 30 dB measurement range. The use of low-frequency substitution or high-frequency substitution can widen its measurement range and reduce the test error. In addition, frequent calibration of the detector crystal is also a way to reduce errors. 4.1.4.1 Low-frequency substitution method: When the signal received by the test line changes, the low-frequency attenuator at the input of the amplifier is changed to keep the output signal of the amplifier unchanged. The change value of the low-frequency attenuator represents the change value of the received signal. Since the working state of the amplifier is the same as that of the amplifier, the disadvantage of the small dynamic range of the amplifier is avoided. 4.1.4.2 High-frequency substitution method: When the signal received by the test antenna changes, the high-frequency attenuator at the transmitting signal source end is changed to keep the output signal of the amplifier unchanged. The change value of the high-frequency attenuator represents the change value of the received signal. Since the working state of the amplifier and the detector has not changed, the disadvantage of the small dynamic range of the amplifier and the detector is avoided. The high-frequency attenuator has high accuracy, so the typical data measured by the high-frequency substitution method is an error of about ±1dB in the 50dB measurement range.
4.1.5 Simple detector-amplifier system Although the measurement range is small and the error is large, it is widely used in scale model work or testing quasi-isotropic antenna test fields because of its simplicity, convenience, and easy operation.
4.2 When the antenna test requires the receiving system to have a large dynamic range, high sensitivity and frequency discrimination capability, a superheterodyne receiver for antenna measurement is used. This receiver can operate over a wide frequency band from a few megahertz to tens of gigahertz or even higher.
4.2.1 The receiver is usually placed in the main control console and the test antenna can be placed far away. The pre-amplifier, first mixer and pre-mid amplifier of the receiver are preferably directly connected to the port of the test antenna. This can avoid excessive attenuation of the cable causing performance degradation or the trouble of long waveguide routing. 4.2.2 The receiver is preferably equipped with manual and motor-driven tuning mechanisms. Motor control can be used to perform mechanical automatic frequency adjustment and make the receiver suitable for sweep frequency measurement. 4.2.3 Since the antenna pattern recorder generally operates on a fixed 1kHz audio carrier frequency, this requires the output of the receiver to be 1KHz. The antenna pattern test field receiver can be designed to receive continuous waves and introduce 1KHz amplitude modulation inside the receiver. This eliminates the need to adjust the modulation frequency of the signal source on-site or remotely. 4.2.4 If the frequency of the signal source is not stable enough to eliminate significant frequency drift, automatic frequency control must be used. The local oscillator may also require automatic frequency control to compensate for frequency drift. The automatic frequency control system should be able to operate over an input signal dynamic range greater than 40dB. 4.2.5 Sometimes a useful circuit is installed in the test receiver to compensate for changes in the power level of the transmitting signal source. This circuit requires continuous monitoring of the signal from the transmitting signal source during the measurement. 4.3 For measurement occasions requiring higher sensitivity, accuracy and larger dynamic range, a double conversion phase-locked receiver can be used.
4.3.1 The double conversion phase-locked receiver uses frequency conversion rather than square law detection to generate the required 1kHz output signal. The use of phase locking technology can differentiate such a low second intermediate frequency. A block diagram of a single-channel double conversion and phase-locked heterodyne receiver system is shown in Figure 2. 4.3.2 The bandwidth of the first intermediate frequency amplifier in the system is about 10MHz. The bandwidth of the second intermediate frequency amplifier is about 100Hz, and the noise bandwidth of the double conversion system is approximately equal to twice the receiver output bandwidth, that is, 200Hz. The bandwidth of an ordinary receiver using square law detection is about 10kH2. Obviously, the sensitivity of a double conversion phase-locked receiver is greatly improved compared to an ordinary receiver.
4.3.3 Another advantage of a double conversion phase-locked receiver is that the output voltage changes linearly with the input voltage rather than with the input power5
SJ2534.1-84
In a receiver using square law detection, the output voltage needs to change by 10000:1 to represent the input voltage. In a secondary conversion phase-locked receiver, as long as the output voltage changes by 100:1, it represents the input voltage change by 100:1. Therefore, it is very easy for the system to achieve a dynamic range of 60dB, which meets the requirements of most measurements. Careful design can also increase the dynamic range to 80dB. 4.3.4 The double-conversion phase-locked receiver can also select the output frequency to increase the data rate as needed. For example, if the output frequency is increased to increase the output bandwidth to 10 times, the data rate of this receiver is also increased to 10 times, and the system sensitivity is correspondingly reduced by 10dB.
4.3.5 The reference signal required by the phase-locked receiver can be obtained by the reference antenna. In short-distance situations, it is directly taken out from the signal source.
4.4 General phase measurement requires corresponding test equipment. The measurement line method, bridge method, modulation method, etc. can all be used for phase testing. A general digital phase meter can directly read the phase. The block diagram of a dual-channel double-conversion phase-locked receiver for accurate phase measurement is shown in Figure 3.
4.4.1 The circuit of Figure 3 is similar to that of Figure 2. The difference is that it has two signal channels, A and B. They are both fed by the same first and second local oscillators. The output voltage of each channel is proportional to the microwave input voltage of the channel. The signal level of each channel can be changed independently within the dynamic range of the system. 4.4.2 The key to this system is to eliminate interference between channels. Through the use of isolators, proper shielding and careful design, the isolation between channels can be greater than 90dB. Such a large isolation causes a linear error of less than ±0.25dB within a 60dB dynamic range.
Multi-channel mixer
Signal channel amplifier
RF input
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Intermediate amplifier
Phase detector
Intermediate amplifier
Mixer
45.00tMHz
Mixer
Figure 3 Dual-channel heterodyne receiving system for phase measurement 1 2
H Output
Channel B
Anju Output
4.4.3 When the two input signals are heterodyned to a frequency of 1 kHz, the phase measurement essentially becomes a time measurement. In Figure 3, each 1 kHz output signal is fed to a zero-crossing detector. Each zero-crossing detector can detect the positive zero-crossing time of the input 1kHz signal and generate a narrow pulse output. The measurement of the zero-crossing time interval of the signals of channel A and channel B can directly indicate the degree of the RF signal. With this system, the amplitude changes of the signals in the two channels and the phase difference between them can be measured simultaneously. The amplitude and phase are read in analog or digital form according to different requirements.
4.5 High measurement accuracy can be obtained by using precision cutoff or attenuator in the receiver system. Typical data is that the test error is about 0.5dB in a measurement range of 60dB. 4.6 In the automated test system, the receiver should be able to interface directly with the computer. If the operating frequency must be changed during the measurement process, a local oscillator that is easy to adjust should be equipped. 4.7 It is allowed to equip other necessary testing equipment according to specific test items and test requirements. 5 Positioning system
5.1 Antenna positioner
5.1.18 Rotational and mid-rotational axes
Two orthogonal axes are required for true and mid-cutting, whether for fixed or movable aim-push-line methods. These are usually called the 0-axis and the mid-axis and are shown in Figure 4. The θ-axis is the oz-axis of the coordinate system and allows cutting in the mid-direction with 0 as the parameter. The θ-axis coincides with the OA line drawn through the origin. The OA line is in turn perpendicular to the OS line which defines the direction of the source antenna. The 0-axis allows cutting in the direction with the mid-direction as the parameter. These two axes are used in all spherical coordinate positioner configurations.
5.1.2 Positioner for movable aim-line systems A positioner configuration for a movable aim-line system is shown in Figure 5. It consists of a bridge for rotation in the 0-direction and an azimuth positioner for rotation in the mid-direction. Since the distance between the two antennas in this scheme is limited, it is only suitable for testing small antennas. For example: the primary feed of a reflector. Another way to use the bench-type solution is to mount the source antenna on a bracket that moves along a fixed semicircular arc centered on the turntable on which the test antenna is mounted. Controlling the movement of the bracket and turntable can obtain a cut in the mid-direction. This type of test field is mainly used to test VHF and UHF antennas mounted on aircraft and scale models of high-frequency antennas. Mid-rotation axis
Special rotation axis
Figure 4 Two orthogonal rotation axes required by the antenna positioner when using spherical coordinates
5.1.3 Positioners for fixed line of sight systems For fixed line of sight systems, all rotations in the 0 and 0 directions are provided by the test antenna positioner. The two types of positioners that meet the requirements of this system are the azimuth-pitch type and the pitch-azimuth type. For the commonly used inclined test field, the use of azimuth-pitch positioners for measurements is more in line with the definition of antenna measurement. The two positioners and their associated coordinate systems are shown in Figure 6. Another example of an elevation-azimuth positioner is a model tower (see Figure 7). The use of additional axes can give greater flexibility. For example, an azimuth-elevation-azimuth positioner is often used (see Figure 8). ||Figure 6 Two standard positioners and their associated spherical coordinate system rotation
Central rotation axis
Figure 7 Model tower and its associated spherical coordinate system
e Rotation axis
Central rotation axis
Central rotation axis
Elevation axis
SJ2534.1-84
Azimuth axis
Azimuth axis
Direct moving multiple source
Figure 8 Azimuth axis—azimuth positioner
5.1.4 Coordinate system consistency
To facilitate the interpretation of measurement data and estimation of errors, the operating coordinate system of the test antenna should be consistent with the coordinate system of the positioner.
5.1.5 Selection of positioner
The physical characteristics of the test antenna and the general shape of its radiation pattern are two important factors to be considered when selecting a positioner. Sometimes a positioner must be designed to meet special measurement requirements that require nonstandard motion. 5.1.6 Special Positioners
When the radiation pattern of the antenna under test is essentially isotropic, a specially designed positioner may be required. This positioner will not significantly change the radiation pattern of the antenna under test. One method is to hang the antenna from the end of a long non-Golden Eagle pole. Another method is to mount the antenna on a foam plastic tower, 5.1.7 Measurements with Orthogonal Polarizations
If the measurement requires orthogonal polarization, the polarization of the source antenna should be able to be electrically converted between two orthogonal linear polarizations or two orthogonal circular polarizations. For orthogonal linear polarization, some measurement methods require that the polarization direction be rotated 360 degrees continuously during the measurement, but a more common method is to use a positioner that rotates the linearly polarized source antenna at least 180 degrees. 5.2 Antenna Positioner Errors
In radiation pattern measurements, the errors introduced by the positioner are angular errors or pointing errors. The following are various errors related to positioners.
5.2.1 Geometric position error
a, coordinate axis alignment error, the coordinate system of the test antenna is not aligned with the coordinate system of the antenna positioner. b, orthogonality error, the two rotation axes of the antenna positioner are not orthogonal. c, collimation error, the axis is not orthogonal to the straight line from the coordinate origin of the positioner to the source antenna (OS line in Figure 4) d, axis deflection and vibration.
5.2.2 Axis position error
Error caused when determining the axis position angle.
5.2.3 Flexural error
SJ2534.1-84
Changes in the structure of the positioner caused by thermal expansion and contraction and changes in the forces applied to the positioner. 5.2.4 Geometric error
Some geometric errors are inherent in the design and manufacture of the positioner. For a well-designed positioner, these errors are generally small and determined by the data provided by the manufacturer. The errors caused by the installation of the positioner and the test antenna must be controlled. More attention should be paid when installing the test antenna on the positioner. 5.2.5 Measurement of shaft angle data
Shaft angle data can be obtained using a synchronization system, potentiometer or digital encoder. Generally, the positioner uses a dual synchronization system, and the transmission ratio of its transmitter to each axis is 1:1 and 36:1. The read-out output system can be analog or digital. The analog type consists of a synchronous receiver indicator, while the digital type requires an analog-to-digital converter. The read-out error is related to the components involved and is generally about 0.05 to less than 0.01. Direct-driven digital encoders are more accurate than transmission synchronization systems and are suitable for use when high precision is required. High-precision digital encoders can be multi-stage rotary transformer type or optical type. The microprocessor controls the stepper motor to drive the antenna positioner, which not only saves the synchronization system or optical encoder, but also facilitates data processing.
5.2.6 Measures to reduce bending errors
Bending errors caused by solar thermal radiation can be reduced by solar reflectors, heat insulation screens, reflective paints and shielding layers, and their size can be monitored by appropriate detection equipment. In order to reduce the bending errors caused by the change of the bending moment applied to the antenna installation surface, the usual method is to add a counterweight balance when designing the antenna base to reduce the change of the bending moment. It is also possible to predict the deflection caused by the bending moment in advance and give a correction coefficient for the relevant angle to correct the error. 6 Antenna pattern recorder
6.1 Recording of antenna pattern
6.1.1 Simple test
In the simple test, the method of manual point-by-point test can be used to depict the antenna pattern. 6.1.2 Antenna pattern recorder
The antenna pattern recorder provides us with a means of intuitively displaying the antenna pattern. The recorder plots the relative signal strength received by the antenna under test as a function of the angular position of the antenna. Depending on the type of receiving system used, the signal can be obtained from the output of the receiver or directly from the microwave detector. The angular position data can generally be obtained from a synchronous transmitter or digital encoder that is coupled to the positioner shaft. If the receiving system can provide a DC output with an amplitude proportional to the RF phase angle, the recorder can also record the relative phase angle between the two signals. 6.2 Composition of an Antenna Pattern Recorder
A typical antenna pattern recorder is a motor-driven device that uses a servo system to drive the recorder shaft.
6.2.1 Determination of the angular position of the antenna
The recording paper servo system determines the position of the recording paper as a function of the angular position of the antenna. 6.2.2 Determination of the input signal amplitude
The recording pen servo system drives the position of the recording pen in response to the input signal amplitude. 113 Positioners for Fixed Boresight Systems For fixed boresight systems, the rotations of 0 and y are all provided by the antenna positioner under test. Two types of positioners that meet the requirements of this system are the azimuth-elevation type and the elevation-azimuth type. For the commonly used inclined test fields, the use of an azimuth-elevation positioner for measurements is more in line with the definition of antenna measurements. The two types of positioners and their associated coordinate systems are shown in Figure 6. Another example of an elevation-azimuth positioner is the model tower (see Figure 7), where greater flexibility can be achieved by using additional axes. For example: Azimuth-elevation-azimuth locator is often used (see Figure 8) Jinghua rotator
Source antenna
Test antenna
Middle exchange axis
Bridge-shaped platform Cui generation
8 Square carbon rotation
9 Exchange axis
Figure 5 A locator structure, in which the source antenna is supported by a directional rotation bracket
Middle exchange axis
White rotation axis
e rotation axis
Middle rotation axis
Azimuth-elevation locator
SJ2534.1-84
e rotation axis
Attached azimuth locator||tt ||Figure 6 Two standard positioners and their associated spherical coordinate system rotation
Central rotation axis
Figure 7 Model tower and its associated spherical coordinate system
e Rotation axis
Central rotation axis
Central rotation axis
Elevation axis
SJ2534.1-84
Azimuth axis
Azimuth axis
Direct moving multiple source
Figure 8 Azimuth axis—azimuth positioner
5.1.4 Coordinate system consistency
To facilitate the interpretation of measurement data and estimation of errors, the operating coordinate system of the test antenna should be consistent with the coordinate system of the positioner.
5.1.5 Selection of positioner
The physical characteristics of the test antenna and the general shape of its radiation pattern are two important factors to be considered when selecting a positioner. Sometimes a positioner must be designed to meet special measurement requirements that require nonstandard motion. 5.1.6 Special Positioners
When the radiation pattern of the antenna under test is essentially isotropic, a specially designed positioner may be required. This positioner will not significantly change the radiation pattern of the antenna under test. One method is to hang the antenna from the end of a long non-Golden Eagle pole. Another method is to mount the antenna on a foam plastic tower, 5.1.7 Measurements with Orthogonal Polarizations
If the measurement requires orthogonal polarization, the polarization of the source antenna should be able to be electrically converted between two orthogonal linear polarizations or two orthogonal circular polarizations. For orthogonal linear polarization, some measurement methods require that the polarization direction be rotated 360 degrees continuously during the measurement, but a more common method is to use a positioner that rotates the linearly polarized source antenna at least 180 degrees. 5.2 Antenna Positioner Errors
In radiation pattern measurements, the errors introduced by the positioner are angular errors or pointing errors. The following are various errors related to positioners.
5.2.1 Geometric position error
a, coordinate axis alignment error, the coordinate system of the test antenna is not aligned with the coordinate system of the antenna positioner. b, orthogonality error, the two rotation axes of the antenna positioner are not orthogonal. c, collimation error, the axis is not orthogonal to the straight line from the coordinate origin of the positioner to the source antenna (OS line in Figure 4) d, axis deflection and vibration.
5.2.2 Axis position error
Error caused when determining the axis position angle.
5.2.3 Flexural error
SJ2534.1-84
Changes in the structure of the positioner caused by thermal expansion and contraction and changes in the forces applied to the positioner. 5.2.4 Geometric error
Some geometric errors are inherent in the design and manufacture of the positioner. For a well-designed positioner, these errors are generally small and determined by the data provided by the manufacturer. The errors caused by the installation of the positioner and the test antenna must be controlled. More attention should be paid when installing the test antenna on the positioner. 5.2.5 Measurement of shaft angle data
Shaft angle data can be obtained using a synchronization system, potentiometer or digital encoder. Generally, the positioner uses a dual synchronization system, and the transmission ratio of its transmitter to each axis is 1:1 and 36:1. The read-out output system can be analog or digital. The analog type consists of a synchronous receiver indicator, while the digital type requires an analog-to-digital converter. The read-out error is related to the components involved and is generally about 0.05 to less than 0.01. Direct-driven digital encoders are more accurate than transmission synchronization systems and are suitable for use when high precision is required. High-precision digital encoders can be multi-stage rotary transformer type or optical type. The microprocessor controls the stepper motor to drive the antenna positioner, which not only saves the synchronization system or optical encoder, but also facilitates data processing.
5.2.6 Measures to reduce bending errors
Bending errors caused by solar thermal radiation can be reduced by solar reflectors, heat insulation screens, reflective paints and shielding layers, and their size can be monitored by appropriate detection equipment. In order to reduce the bending errors caused by the change of the bending moment applied to the antenna installation surface, the usual method is to add a counterweight balance when designing the antenna base to reduce the change of the bending moment. It is also possible to predict the deflection caused by the bending moment in advance and give a correction coefficient for the relevant angle to correct the error. 6 Antenna pattern recorder
6.1 Recording of antenna pattern
6.1.1 Simple test
In the simple test, the method of manual point-by-point test can be used to depict the antenna pattern. 6.1.2 Antenna pattern recorder
The antenna pattern recorder provides us with a means of intuitively displaying the antenna pattern. The recorder plots the relative signal strength received by the antenna under test as a function of the angular position of the antenna. Depending on the type of receiving system used, the signal can be obtained from the output of the receiver or directly from the microwave detector. The angular position data can generally be obtained from a synchronous transmitter or digital encoder that is coupled to the positioner shaft. If the receiving system can provide a DC output with an amplitude proportional to the RF phase angle, the recorder can also record the relative phase angle between the two signals. 6.2 Composition of an Antenna Pattern Recorder
A typical antenna pattern recorder is a motor-driven device that uses a servo system to drive the recorder shaft.
6.2.1 Determination of the angular position of the antenna
The recording paper servo system determines the position of the recording paper as a function of the angular position of the antenna. 6.2.2 Determination of the input signal amplitude
The recording pen servo system drives the position of the recording pen in response to the input signal amplitude. 113 Positioners for Fixed Boresight Systems For fixed boresight systems, the rotations of 0 and y are all provided by the antenna positioner under test. Two types of positioners that meet the requirements of this system are the azimuth-elevation type and the elevation-azimuth type. For the commonly used inclined test fields, the use of an azimuth-elevation positioner for measurements is more in line with the definition of antenna measurements. The two types of positioners and their associated coordinate systems are shown in Figure 6. Another example of an elevation-azimuth positioner is the model tower (see Figure 7), where greater flexibility can be obtained by using additional axes. For example: Azimuth-elevation-azimuth locator is often used (see Figure 8) Jinghua rotator
Source antenna
Test antenna
Middle exchange axis
Bridge-shaped platform Cui generation
8 Square carbon rotation
9 Exchange axis
Figure 5 A locator structure, in which the source antenna is supported by a directional rotation bracket
Middle exchange axis
White rotation axis
e rotation axis
Middle rotation axis
Azimuth-elevation locator
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e rotation axis
Attached azimuth locator||tt ||Figure 6 Two standard positioners and their associated spherical coordinate system rotation
Central rotation axis
Figure 7 Model tower and its associated spherical coordinate system
e Rotation axis
Central rotation axis
Central rotation axis
Elevation axis
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Azimuth axis
Azimuth axis
Direct moving multiple source
Figure 8 Azimuth axis—azimuth positioner
5.1.4 Coordinate system consistency
To facilitate the interpretation of measurement data and estimation of errors, the operating coordinate system of the test antenna should be consistent with the coordinate system of the positioner.
5.1.5 Selection of positioner
The physical characteristics of the test antenna and the general shape of its radiation pattern are two important factors to be considered when selecting a positioner. Sometimes a positioner must be designed to meet special measurement requirements that require nonstandard motion. 5.1.6 Special Positioners
When the radiation pattern of the antenna under test is essentially isotropic, a specially designed positioner may be required. This positioner will not significantly change the radiation pattern of the antenna under test. One method is to hang the antenna from the end of a long non-Golden Eagle pole. Another method is to mount the antenna on a foam plastic tower, 5.1.7 Measurements with Orthogonal Polarizations
If the measurement requires orthogonal polarization, the polarization of the source antenna should be able to be electrically converted between two orthogonal linear polarizations or two orthogonal circular polarizations. For orthogonal linear polarization, some measurement methods require that the polarization direction be rotated 360 degrees continuously during the measurement, but a more common method is to use a positioner that rotates the linearly polarized source antenna at least 180 degrees. 5.2 Antenna Positioner Errors
In radiation pattern measurements, the errors introduced by the positioner are angular errors or pointing errors. The following are various errors related to positioners.
5.2.1 Geometric position error
a, coordinate axis alignment error, the coordinate system of the test antenna is not aligned with the coordinate system of the antenna positioner. b, orthogonality error, the two rotation axes of the antenna positioner are not orthogonal. c, collimation error, the axis is not orthogonal to the straight line from the coordinate origin of the positioner to the source antenna (OS line in Figure 4) d, axis deflection and vibration.
5.2.2 Axis position error
Error caused when determining the axis position angle.
5.2.3 Flexural error
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Changes in the structure of the positioner caused by thermal expansion and contraction and changes in the forces applied to the positioner. 5.2.4 Geometric error
Some geometric errors are inherent in the design and manufacture of the positioner. For a well-designed positioner, these errors are generally small and determined by the data provided by the manufacturer. The errors caused by the installation of the positioner and the test antenna must be controlled. More attention should be paid when installing the test antenna on the positioner. 5.2.5 Measurement of shaft angle data
Shaft angle data can be obtained using a synchronization system, potentiometer or digital encoder. Generally, the positioner uses a dual synchronization system, and the transmission ratio of its transmitter to each axis is 1:1 and 36:1. The read-out output system can be analog or digital. The analog type consists of a synchronous receiver indicator, while the digital type requires an analog-to-digital converter. The read-out error is related to the components involved and is generally about 0.05 to less than 0.01. Direct-driven digital encoders are more accurate than transmission synchronization systems and are suitable for use when high precision is required. High-precision digital encoders can be multi-stage rotary transformer type or optical type. The microprocessor controls the stepper motor to drive the antenna positioner, which not only saves the synchronization system or optical encoder, but also facilitates data processing.
5.2.6 Measures to reduce bending errors
Bending errors caused by solar thermal radiation can be reduced by solar reflectors, heat insulation screens, reflective paints and shielding layers, and their size can be monitored by appropriate detection equipment. In order to reduce the bending errors caused by the change of the bending moment applied to the antenna installation surface, the usual method is to add a counterweight balance when designing the antenna base to reduce the change of the bending moment. It is also possible to predict the deflection caused by the bending moment in advance and give a correction coefficient for the relevant angle to correct the error. 6 Antenna pattern recorder
6.1 Recording of antenna pattern
6.1.1 Simple test
In the simple test, the method of manual point-by-point test can be used to depict the antenna pattern. 6.1.2 Antenna pattern recorder
The antenna pattern recorder provides us with a means of intuitively displaying the antenna pattern. The recorder plots the relative signal strength received by the antenna under test as a function of the angular position of the antenna. Depending on the type of receiving system used, the signal can be obtained from the output of the receiver or directly from the microwave detector. The angular position data can generally be obtained from a synchronous transmitter or digital encoder that is coupled to the positioner shaft. If the receiving system can provide a DC output with an amplitude proportional to the RF phase angle, the recorder can also record the relative phase angle between the two signals. 6.2 Composition of an Antenna Pattern Recorder
A typical antenna pattern recorder is a motor-driven device that uses a servo system to drive the recorder shaft.
6.2.1 Determination of the angular position of the antenna
The recording paper servo system determines the position of the recording paper as a function of the angular position of the antenna. 6.2.2 Determination of the input signal amplitude
The recording pen servo system drives the position of the recording pen in response to the input signal amplitude. 116 Special Positioners
When the radiation pattern of the antenna under test is essentially isotropic, a specially designed positioner may be required. This positioner will not significantly change the radiation pattern of the antenna under test. One method is to hang the antenna from the end of a long non-Golden Eagle pole. Another method is to mount the antenna on a foam plastic tower. 5.1.7 Measurements using orthogonal polarizations
If the measurement requires orthogonal polarization, the polarization of the source antenna should be able to be electrically converted between two orthogonal linear polarizations or two orthogonal circular polarizations. For orthogonal linear polarization, some measurement methods require that the polarization direction be rotated 360 degrees continuously during the measurement, but a more common method is to use a positioner that rotates the linearly polarized source antenna at least 180 degrees. 5.2 Antenna Positioner Errors
In radiation pattern measurements, the errors introduced by the positioner are angular errors or pointing errors. The following are various errors related to the positioner.
5.2.1 Geometric position error
a, coordinate axis alignment error, the coordinate system of the test antenna is not aligned with the coordinate system of the antenna positioner. b, orthogonality error, the two rotation axes of the antenna positioner are not orthogonal. c, collimation error, the axis is not orthogonal to the straight line from the coordinate origin of the positioner to the source antenna (OS line in Figure 4) d, axis deflection and vibration.
5.2.2 Axis position error
Error caused when determining the axis position angle.
5.2.3 Flexural error
SJ2534.1-84
Changes in the structure of the positioner caused by thermal expansion and contraction and changes in the forces applied to the positioner. 5.2.4 Geometric error
Some geometric errors are inherent in the design and manufacture of the positioner. For a well-designed positioner, these errors are generally small and determined by the data provided by the manufacturer. The errors caused by the installation of the positioner and the test antenna must be controlled. More attention should be paid when installing the test antenna on the positioner. 5.2.5 Measurement of shaft angle data
Shaft angle data can be obtained using a synchronization system, potentiometer or digital encoder. Generally, the positioner uses a dual synchronization system, and the transmission ratio of its transmitter to each axis is 1:1 and 36:1. The read-out output system can be analog or digital. The analog type consists of a synchronous receiver indicator, while the digital type requires an analog-to-digital converter. The read-out error is related to the components involved and is generally about 0.05 to less than 0.01. Direct-driven digital encoders are more accurate than transmission synchronization systems and are suitable for use when high precision is required. High-precision digital encoders can be multi-stage rotary transformer type or optical type. The microprocessor controls the stepper motor to drive the antenna positioner, which not only saves the synchronization system or optical encoder, but also facilitates data processing.
5.2.6 Measures to reduce bending errors
Bending errors caused by solar thermal radiation can be reduced by solar reflectors, heat insulation screens, reflective paints and shielding layers, and their size can be monitored by appropriate detection equipment. In order to reduce the bending errors caused by the change of the bending moment applied to the antenna installation surface, the usual method is to add a counterweight balance when designing the antenna base to reduce the change of the bending moment. It is also possible to predict the deflection caused by the bending moment in advance and give a correction coefficient for the relevant angle to correct the error. 6 Antenna pattern recorder
6.1 Recording of antenna pattern
6.1.1 Simple test
In the simple test, the method of manual point-by-point test can be used to depict the antenna pattern. 6.1.2 Antenna pattern recorder
The antenna pattern recorder provides us with a means of intuitively displaying the antenna pattern. The recorder plots the relative signal strength received by the antenna under test as a function of the angular position of the antenna. Depending on the type of receiving system used, the signal can be obtained from the output of the receiver or directly from the microwave detector. The angular position data can generally be obtained from a synchronous transmitter or digital encoder that is coupled to the positioner shaft. If the receiving system can provide a DC output with an amplitude proportional to the RF phase angle, the recorder can also record the relative phase angle between the two signals. 6.2 Composition of an Antenna Pattern Recorder
A typical antenna pattern recorder is a motor-driven device that uses a servo system to drive the recorder shaft.
6.2.1 Determination of the angular position of the antenna
The recording paper servo system determines the position of the recording paper as a function of the angular position of the antenna. 6.2.2 Determination of the input signal amplitude
The recording pen servo system drives the position of the recording pen in response to the input signal amplitude. 116 Special Positioners
When the radiation pattern of the antenna under test is essentially isotropic, a specially designed positioner may be required. This positioner will not significantly change the radiation pattern of the antenna under test. One method is to hang the antenna from the end of a long non-Golden Eagle pole. Another method is to mount the antenna on a foam plastic tower. 5.1.7 Measurements using orthogonal polarizations
If the measurement requires orthogonal polarization, the polarization of the source antenna should be able to be electrically converted between two orthogonal linear polarizations or two orthogonal circular polarizations. For orthogonal linear polarization, some measurement methods require that the polarization direction be rotated 360 degrees continuously during the measurement, but a more common method is to use a positioner that rotates the linearly polarized source antenna at least 180 degrees. 5.2 Antenna Positioner Errors
In radiation pattern measurements, the errors introduced by the positioner are angular errors or pointing errors. The following are various errors related to the positioner.
5.2.1 Geometric position error
a, coordinate axis alignment error, the coordinate system of the test antenna is not aligned with the coordinate system of the antenna positioner. b, orthogonality error, the two rotation axes of the antenna positioner are not orthogonal. c, collimation error, the axis is not orthogonal to the straight line from the coordinate origin of the positioner to the source antenna (OS line in Figure 4) d, axis deflection and vibration.
5.2.2 Axis position error
Error caused when determining the axis position angle.
5.2.3 Flexural error
SJ2534.1-84
Changes in the structure of the positioner caused by thermal expansion and contraction and changes in the forces applied to the positioner. 5.2.4 Geometric error
Some geometric errors are inherent in the design and manufacture of the positioner. For a well-designed positioner, these errors are generally small and determined by the data provided by the manufacturer. The errors caused by the installation of the positioner and the test antenna must be controlled. More attention should be paid when installing the test antenna on the positioner. 5.2.5 Measurement of shaft angle data
Shaft angle data can be obtained using a synchronization system, potentiometer or digital encoder. Generally, the positioner uses a dual synchronization system, and the transmission ratio of its transmitter to each axis is 1:1 and 36:1. The read-out output system can be analog or digital. The analog type consists of a synchronous receiver indicator, while the digital type requires an analog-to-digital converter. The read-out error is related to the components involved and is generally about 0.05 to less than 0.01. Direct-driven digital encoders are more accurate than transmission synchronization systems and are suitable for use when high precision is required. High-precision digital encoders can be multi-stage rotary transformer type or optical type. The microprocessor controls the stepper motor to drive the antenna positioner, which not only saves the synchronization system or optical encoder, but also facilitates data processing.
5.2.6 Measures to reduce bending errors
Bending errors caused by solar thermal radiation can be reduced by solar reflectors, heat insulation screens, reflective paints and shielding layers, and their size can be monitored by appropriate detection equipment. In order to reduce the bending errors caused by the change of the bending moment applied to the antenna installation surface, the usual method is to add a counterweight balance when designing the antenna base to reduce the change of the bending moment. It is also possible to predict the deflection caused by the bending moment in advance and give a correction coefficient for the relevant angle to correct the error. 6 Antenna pattern recorder
6.1 Recording of antenna pattern
6.1.1 Simple test
In the simple test, the method of manual point-by-point test can be used to depict the antenna pattern. 6.1.2 Antenna pattern recorder
The antenna pattern recorder provides us with a means of intuitively displaying the antenna pattern. The recorder plots the relative signal strength received by the antenna under test as a function of the angular position of the antenna. Depending on the type of receiving system used, the signal can be obtained from the output of the receiver or directly from the microwave detector. The angular position data can generally be obtained from a synchronous transmitter or digital encoder that is coupled to the positioner shaft. If the receiving system can provide a DC output with an amplitude proportional to the RF phase angle, the recorder can also record the relative phase angle between the two signals. 6.2 Composition of an Antenna Pattern Recorder
A typical antenna pattern recorder is a motor-driven device that uses a servo system to drive the recorder shaft.
6.2.1 Determination of the angular position of the antenna
The recording paper servo system determines the position of the recording paper as a function of the angular position of the antenna. 6.2.2 Determination of the input signal amplitude
The recording pen servo system drives the position of the recording pen in response to the input signal amplitude. 11
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