GB/T 11298.2-1997 Measurement methods for satellite television earth receiving stations - Antenna measurements
Some standard content:
GB/T11298.2—1997
This standard is the measurement method of satellite TV earth receiving station antenna. According to the electrical performance required by 4.2 in GB/T11442-1995 "General Technical Conditions for Satellite TV Earth Receiving Station", GB11298.2--89 "Measurement Method Antenna Measurement for Satellite TV Earth Receiving Station" is revised. With the development of science and technology, the detection instruments are constantly updated. The original national standard GB11298.2 can no longer meet the detection requirements and must be revised. This standard mainly makes the following revisions to the original content: delete the radio star measurement method and add the satellite method; - Use the spectrum analyzer to sweep the frequency to measure the antenna noise temperature. From the date of implementation, this standard will replace GB11298.2--89. This standard is proposed by the Ministry of Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of the Standardization Research Institute of the Ministry of Electronics Industry. The drafting units of this standard are: the 54th Research Institute of the Ministry of Electronics Industry and the Broadcasting Science Research Institute of the Ministry of Radio, Film and Television. The main drafters of this standard are: Wang Jiuzhen and Zhao Peng. This standard was first issued in March 1989 and revised for the first time in August 1997. 15
1 Scope
National Standard of the People's Republic of China
Methods of measurement for satellitetelevision earth receive-only stationAntenna measurement
GB/T 11298.2—1997
Replaces GB11298.2—89
This standard specifies the definition, measurement conditions and measurement methods of satellitetelevision earth receive-only station antenna performance indicators. This standard applies to the measurement of satellitetelevision earth receive-only station antenna performance. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB11298.1-1997 Satellite TV Earth Receiving Station Measurement Method System Measurement GB/T14733.10--93 Telecommunication Terminology Antenna 3 Definitions
Except for the following definitions, this standard adopts the definitions in GB/T14733.10. 3.1 Antenna sub-system The antenna sub-system is a part of the satellite TV receiving equipment, which consists of an antenna and a feed network (see Figure 1). Antenna
Feed network
Receiver outdoor unit
Figure 1 Antenna sub-system
The antenna consists of a main reflector, a primary radiator, and sometimes a sub-reflector. The feed network usually includes a polarizer and a transition waveguide, which is connected to the outdoor unit through a waveguide feeder. 3.2 Gain standard antennagain standard antennaApproved by the State Administration of Technical Supervision on August 26, 199716
Implementation on March 1, 1998
GB/T11298.2—1997
Gain standard antenna is an antenna with a certain structure and accurately calibrated. The gain coefficient and directivity coefficient of the antenna are numerically close to each other. In addition, the calculated value of the antenna gain coefficient is very close to the measured value. Therefore, horn antennas are often used as comparison standards for testing microwave antenna gain.
3.3 Axial polan
Axial polan is the electric axis direction, which is the axial direction determined by the radiation performance of the antenna. 3.4 Axial ratio (or ellipse ratio) Axial ratio (or ellipse ratio) is the ratio of the major axis to the minor axis of the polarization ellipse. 3.5 Polarizationpolarization
Polarization is the shape and orientation of the trajectory of the end point of the electric field vector changing with time. The end point trajectory can be an ellipse, a circle or a straight line within one electromagnetic oscillation cycle. The polarization is called elliptical polarization, circular polarization or linear polarization accordingly. 3.6 Cross-polarization discrimination The cross-polarization discrimination of a receiving antenna is the ratio of the power received by the antenna from the polarization (co-polarization) with the expected maximum power transmission in a given direction to the power received from the same far-field radiator with equal power but orthogonal polarization in the same direction. 3.7 Antenna power gain Antenna power gain means the total gain relative to an isotropic lossless source, which is the sum of the gain components of two orthogonal polarizations. If the gain of a certain polarization is referred to, this polarization should be indicated, for example, "right-hand circular polarization gain" or "horizontal linear polarization gain". The definition of the receiving antenna gain G can also be derived from the effective area A. See formula (1) and formula (2): G = 4TA
（1）
Where: λ—operating wavelength, m;
A—effective area of receiving antenna, m\; P.—effective power on the matching terminal of receiving antenna, W; S—power per unit area of plane wave on the receiving antenna mouth, W/m2. 3.8 Antenna radiation pattern antenna pala
The receiving antenna pattern is a graphical description of the antenna's ability to receive plane waves of equal amplitude as the antenna's pointing angle changes. The plane wave of equal amplitude that illuminates the antenna under test is generated by a fixed point source set in the far field, and the size of the receiving ability is expressed as the power level displayed by the receiver connected to the antenna.
When the polarization of the antenna under test is consistent with the polarization of the far-field source antenna, the resulting pattern is called the co-polarization pattern of the antenna; when the polarization of the antenna under test is orthogonal to the polarization of the far-field source antenna, the resulting pattern is called the cross-polarization pattern of the antenna, and the level of the cross-polarization pattern should be normalized according to the peak value of the co-polarization pattern. When measuring the pattern, the pattern of different planes is obtained depending on the orientation of the rotation axis that changes the antenna pointing angle. When the rotation axis is perpendicular to the antenna When the azimuth (or elevation) axes of the lines are consistent, the resulting directional pattern is called the horizontal (or plumb) plane directional pattern. When the rotation axis is at 0°, 90° and 45° angles to the polarization plane of the antenna, the resulting directional patterns are called E-plane directional patterns, H-plane directional patterns and 45° plane directional patterns. 4 Measurement method
4.1 Atmospheric conditions
Generally, it refers to the on-site atmospheric environmental conditions, requiring sunny days and light breezes. 4.2 Environmental conditions
In the test area that meets the antenna far-field criteria, there should be no buildings, trees or other objects that cause reflections. 4.3 Requirements for measuring instruments
The frequency of the signal source must remain stable, requiring a frequency stability of 10-4 to 10-' within 30 minutes, and the output power is generally required to be 0~～17
GB/T 11298.2-1997
33dBm. If the requirements are not met, a power amplifier can be added. The spectrum analyzer can still work stably when the resolution bandwidth is less than 100Hz, and the dynamic range must be above 60dB.
4.4 Requirements for test sites
In order to determine the performance of far-field antennas, the ideal test site should provide a plane wave with uniform amplitude to illuminate the antenna aperture. Here, it is stipulated that a nearly ideal free space test site should be used. In this area, the influence of surrounding objects should be minimized, including reflections from the surface of the test site, the source antenna and the test tower. A reflection test site can also be used. It is usually stipulated that the phase difference between the center and edge of the antenna aperture to be tested is less than π/8, and the minimum test distance is determined as follows: R≥2De
·（3）
Diameter of the antenna aperture to be tested; m;
Where: D
Input——operating wavelength, m;
Distance from the antenna to be tested to the signal source, m.
4.5 Antenna power gain
The measurement of antenna power gain is usually carried out by direct comparison method, amplitude modulation signal method, direct calibration method, satellite method and radio star measurement method. This standard recommends the use of direct comparison method and satellite method.
4.5.1 Direct comparison method
4.5.1.1 Measurement principle
The comparison method of gain measurement is to compare the signal levels received by the gain standard antenna and the antenna to be tested from the radiation source at the same distance. The measurement block diagram is shown in Figure 2.
Antenna to be tested
4.5.1.2 Measurement steps
a) Connect the equipment according to Figure 2;
Low noise
Amplifier
Gain standard antenna
Spectrometer
Figure 2 Direct comparison method measurement block diagram
Printer
b) Turn the switch to the antenna under test, adjust the antenna under test and the radiation source to match the polarization, and record the received power level PAc) Turn the switch to the gain standard antenna, aim at the radiation source and continuously change the height of the gain standard antenna up and down, and record the maximum value Prma and the minimum value Prmin of the received signal level; d) The power gain of the antenna under test is expressed by formulas (4a) and (4b): G=G, -(PA- Pm)+10 lg1β
β= 10 Pmr _ Pm
Where: G is the power gain of the antenna under test, dB; G is the gain of the gain standard antenna at the test frequency, dB; - the receiving level of the antenna under test, dBm;
β--ground reflection correction coefficient;
( 4a )
（4b）
GB/T 11298. 2-1997
- the maximum receiving level of the gain standard antenna, dBm; Prmin--the minimum receiving level of the gain standard antenna, dBm. 4.5.2 Satellite method
4.5.2.1 Measurement principle
Use the beacon on the synchronous satellite as the signal source to measure the azimuth and elevation pattern 3dB beam width of the antenna under test, and then derive the gain of the antenna under test according to the empirical formula. Calculation formula (5): G = 10 lg(z6)
f270001
Where: 8Az, 8L——Are the 3dB widths of the azimuth and elevation beams. 4.5.2.2 Measurement steps
a) Connect the equipment as shown in Figure 3;
Low noise
Amplifier
Analyzer
Figure 3 Antenna receiving characteristic measurement block diagram
Printer
b) Accurately align the selected satellite, receive the satellite beacon and fine-tune the antenna to achieve the maximum level; c) Measure the elevation and azimuth directional patterns of the antenna to be tested respectively, and determine QAz and GEL; d) Calculate the antenna gain according to formula (5); e) Determine other frequency points. When selecting another satellite, the steps are the same as b) to d). Note: This method is also applicable to far-field measurements. 4.6 Antenna noise temperature
Antenna noise temperature is usually measured using the Y factor method. 4.6.1 Measurement principle
Antenna noise temperature (TA) is measured using the Y factor method, as expressed by formula (6): TA = T + T - TR
Where: T. — Test environment temperature, K;
TR — Low noise amplifier noise temperature, K; Definition of Y factor:
— The noise power of the standard load and antenna at room temperature, W respectively. Where: Ph, PA—
4.6.2 Measurement steps
a) Pre-calibrate the noise temperature (TR) of the low noise amplifier (LNA) with standard cold and hot loads; b) Connect the equipment according to Figure 4 (cold load is not required at the test site); (5)
(6)
Normal temperature load
Test antenna
GB/T11298.2—1997
Low noise
Amplifier
Waveguide switch
Ling load
Analyzer
Calibration system
Figure 4 Equipment configuration for measuring antenna noise temperature c) Connect the low noise amplifier to the load at normal temperature; d) Set the spectrum analyzer panel controller as follows; Frequency span (SPan)
Preset according to the specified working frequency band;
Attenuator OdB;
dB/div1 dB;
Center frequency is preset as specified, such as: 3.95GHz; Resolution bandwidth 1 MHz.
Printer
e) Turn on the power of the low noise amplifier, scan the noise power curve within the specified frequency band, and store it to obtain Ph; f) Connect the low noise amplifier to the antenna and repeat step e at the specified antenna elevation angle to obtain Pa; i) Print and record the test results and test environment temperature, and check the Y factor of the corresponding frequency point on the curve; h) Use formula (6) and formula (7) to calculate the antenna noise temperature at the corresponding frequency point. 4.6.3 Relationship between the noise temperature TA of the antenna subsystem (including the network) and the antenna noise temperature T. The reference point for measuring TA is at the output flange of the antenna network, and the reference point for examining the antenna noise temperature T. is at the output port of the primary radiator. Assuming that the loss of the feed network is L (dB), the relationship between TA and T. is shown in formula (8): TA T,10-0.1L +(1 - 10-0.1L)T. Where: T. is the test environment temperature, K.
4.7 Antenna voltage standing wave ratio or return loss
4.7.1 Measurement principle
Assume that the input impedance of the antenna is Z. When it is connected to a transmission system with a nominal impedance of Z., a reflected wave with a voltage reflection coefficient of β is generated in the rear transmission system due to impedance mismatch. The degree of this impedance mismatch is usually expressed by the voltage standing wave ratio VSWR or return loss L, or by the reflection coefficient. The relationship between the above parameters is shown in formula (9) to formula (11). zz.
z+z.
L= 20 lgl =
4.7.2 Measurement method
The voltage standing wave ratio or return loss of the antenna is measured by the point frequency method or the sweep frequency method. 4.7.2.1 Point frequency method measurement
（9）
.（10）
The equipment configuration for point frequency method measurement is shown in Figure 5. The measurement accuracy mainly depends on the accuracy of the measuring line itself. With good system configuration, the measurement accuracy of voltage standing wave ratio is usually within 0.01. Signal generator
Isolator
GB/T 11298.2--1997
Low-pass filter
Radio attenuator
Figure 5 Equipment configuration for measuring voltage standing wave ratio
Indicator
Antenna under test
Broadband
When measuring, first connect a short-circuiter to the output port of the measuring line, and calibrate the β-1 indicator scale at the measuring frequency point; then remove the short-circuiter and connect the antenna under test. According to the calibrated scale, the VSWR of the antenna under test can be directly read. 4.7.2.2 Sweep frequency method
The equipment configuration of the sweep frequency method is shown in Figure 6. Directional coupler directivity has a great influence on measurement accuracy, and usually requires a directivity of more than 40dB.
Signal generator
Isolator
Directional coupler
Spectrometer
Figure 6 Equipment configuration of frequency sweep method
Short circuit
Printer
The spectrum analyzer is used as a frequency sweep receiver here. When measuring: first connect a short circuit to the output port of the measurement network (such as directional coupler), make a calibration curve of β=1, L=0dB within the working frequency band and store it; then connect the antenna to be measured, sweep the return loss within the working frequency band and print the measurement results. 4.7.3 Result representation
The measurement results should be represented by a curve or a photo on a scaled oscilloscope or a curve graph drawn by a printer. When the results are not represented by a graph, they should be represented as follows: within the working frequency band, the return loss is greater than ×XdB. The maximum error of the measurement results under various conditions should also be given. 4.8 Antenna Pattern
4.8.1 Measurement Principle
The antenna under test is aligned axially with the source antenna, illuminated by the uniform incident field of the source antenna, and measured at the specified frequency and polarization state. The turntable rotates in the required plane and within the required angle range, while recording the received signal. Data is collected at the selected sampling interval, and the pattern data is displayed in real time or after the fact.
4.8.2 Equipment Configuration for Measuring Antenna Pattern
The equipment configuration for measuring antenna pattern is shown in Figure 7. 21Www.bzxZ.net
4.8.3 Measurement steps
Signal source
Source antenna
GB/T 11298.2-1997
Azimuth axis
Antenna axis
Antenna under test
Elevation axis
Spectrum analyzer
Antenna mount
Figure 7 Equipment configuration for measuring antenna radiation pattern
a) Set up the source antenna and the antenna under test as required; b) Align the antenna under test with the source antenna and calibrate the azimuth (or elevation) scale, zero degree position; computer or
printer
c) The antenna under test rotates its pointing angle continuously or stepwise around the azimuth (or elevation) axis of the antenna, and records the received power level expressed as a function of angle.
4.8.4 Result Representation
Whether it is a co-polarization pattern or a cross-polarization pattern, it should be normalized to the peak value of the co-polarization pattern. The complete pattern data must also indicate the following items:
a) measurement frequency;
b) antenna polarization;
c) measurement plane.
When the results are not presented graphically, typical data should be given as follows: such as half-power beamwidth: X°
first sidelobe level: XXdB;
wide-angle sidelobe envelope: meets (or does not meet) technical requirements. 4.9 Antenna Polarization
4.9.1 Cross-polarization discrimination measurement of linearly polarized antennas The antenna under test is installed on the test field and illuminated by a linearly polarized source antenna located in the far field. The two antennas should be nominally co-polarized and accurately placed at the maximum gain position to record the received power Pm (mW). The source antenna is then rotated around its beam axis to the position of minimum power transmission (polarization zero point), and the received power Pmin (mW) is recorded. The cross-polarization discrimination XPD is given by formula (12): XPD
4.9.2 Circularly polarized antenna axial ratio
The antenna under test is installed in the test field and illuminated by a standard linearly polarized source antenna located in the far field. The two antennas are precisely set at the position of maximum gain according to 4.9.1. The source antenna is rotated at least 180° around its beam axis, and the maximum received power Pmax and the minimum received power Pmin are observed. The axial ratio r is expressed in formula (13).
(13)
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