GB/T 11299.12-1989 Satellite communication earth station radio equipment measurement methods Part 3: Subsystem combination measurement Section 2: 4~6GHz receiving system quality factor (G/T) measurement

This standard specifies the measurement method of the quality factor (G/T) of the 4~6GHz earth station receiving system. One method is to use a star with known power spectrum flux at the earth station and take into account the errors caused by various parameters. An indirect measurement method is also given. GB/T 11299.12-1989 Satellite communication earth station radio equipment measurement method Part 3: Subsystem combination measurement Section 2: 4~6GHz receiving system quality factor (G/T) measurement GB/T11299.12-1989 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Methods of measurement for radio equipment used in satellite earth stationsPart 3: Methods of measurements for combination of sub-systemsSection Two-Measurement of the figure of merit (G/T)of the receiving system in the 4GHz to 6GHz rangeThis standard is part of the series of standards "Methods of measurements for radio equipment used in satellite earth stations for satellite communication"GB11299.12---89
IEC 510-3-2(1980)
This standard is equivalent to the International Electrotechnical Commission standard IEC510-3-2 "Methods of measurement for radio equipment used in satellite earth stations for satellite communicationPart 3: Combination of sub-systemsSection Two-Measurement of the figure of merit (G/T)of the receiving system in the 4GHz to 6GHz range". 1 Subject matter and scope of application
This standard specifies the measurement method of the quality factor (G/T) of the earth station receiving system in the range of 4 to 6 GHz. One method is to use a satellite with a known power spectrum flux density at the earth station and take into account the errors caused by various parameters. An indirect measurement method is also given. 2 Definitions
2.1 Quality factor (G/T)
The quality factor (G/T) of the earth station receiving system is the ratio of the receiving antenna gain to the system noise temperature (reduced to the antenna subsystem output gain dish). The G/T value can usually be expressed as follows: G/T=10 log1o system noise temperature (K) Antenna power gain
(dB/K)
The G/T value can also be calculated to other places in the receiving system, such as the input of the low noise amplifier. In this case, the gain and noise temperature should be converted to the input of the low noise amplifier, but the G/T value remains unchanged. The receiving system noise temperature also includes the contribution of the noise temperature generated by the parts after the test point. Note: When measuring the quality factor (G/T), the transmitter should operate at the maximum rated power. If the operation of the transmitter causes the G/T value of the receiving system to decrease, the decrease value should be indicated in the result.
2.2 Radio stars
Radio stars are a type of microwave cosmic noise power source. The characteristics of four radio stars are known with sufficient accuracy to measure the G/T value. These four stars are Cassiopeia A, Taurus A, Cygnus A and Orion A. Appendix A (reference) introduces the characteristics of these four stars. Note: The moon and the sun can also be used as radio sources to measure the G/T value. 2.3 Standard atmosphere
The standard atmosphere conditions determined in the first section of this series of standards, “General Provisions”, are: Temperature 20℃
Relative humidity 65%
Approved by the Ministry of Electronics Industry of the People’s Republic of China on March 1, 1989 and implemented on January 1, 1990
Vapor pressure 101.3kPa
3General considerationswwW.bzxz.Net
GB11299.1289
When the traffic density transmitted from the satellite to the ground is given, the quality factor (G/T) is a key parameter of the earth station that determines the carrier-to-noise ratio at the input of the demodulator. Therefore, the G/T value of the receiving system must be determined with the highest accuracy. There are two main methods for determining the quality factor (G/T), namely the direct method and the indirect method. The first method is to directly measure the radio star (
T value, the first method is to measure the receiving antenna gain and system noise temperature separately. For large antennas, the direct measurement method is generally recommended because it provides the highest accuracy, which will be described in detail below. When the antenna controllability is limited or the location cannot see the known radio star well at any specified angle, the indirect measurement method must be used.
The G/T value is usually measured under the following conditions:
The elevation angle is any angle between 5° and the maximum operating angle; a.| |tt||Frequency is the center frequency of the receiving band and the frequency close to the edge of the band; specified polarization:
Sunny day;
Light wind.
4Measurement of quality factor (G/T) using calibrated radio stars 4.1Analytical formula of G/T value as a function of Y factor It is well known that radio stars emit microwave noise power. When the earth station receiving antenna is pointed at the radio star, the noise power received by the antenna increases by the following value:
Where: P-
P.-S.A+B_S.*:GB (w)
The increase in noise power when a large line points to a radio star, W; 8 yuan
The power spectrum flow density of the radio source at the measurement frequency, W/m2/Hz; A
The effective area of ​​the receiving antenna, m\;
-The noise bandwidth of the receiver, Hz;
G-The receiving gain of the antenna at the specified frequency; >--The working wavelength, m.
The coefficient 2 appears in the above formula because the polarization mode of the receiving system is given, while the polarization of the radio star is usually random. The monitored radio source is a point source, and this equation is valid only when its radiation wave passes through an atmosphere without attenuation. In fact, neither of these two conditions is true. Therefore, equation (2) must be changed to the following form:
8r.K.·K?
Where: K≥—a correction factor for atmospheric attenuation; K,≥1-
Correction factor related to the angular spread of the radio source. Assuming that Po is the total noise power when the antenna points to the cosmic source, and P is the noise power when the antenna points to the background sky at the same elevation angle, then:
P Piot P,
武中;P.--K·T·B;
T\The noise temperature of the receiving system including the sky noise temperature. According to the above equation, the quality factor (G/T) can be expressed as: G/T 8元k :KuK
GB11299.12-89
Formula 1: k~—Boltzmann constant 1.38×1023 (J/K). The Y factor is the ratio of the noise power received when the antenna is pointed at the cosmic source to the noise power received when the antenna is pointed at the background sky at the same elevation angle. The definitions of all other parameters are the same as in the above equations. This method has a major advantage over the method of determining the G/T value by measuring the values ​​of ( and T separately, that is, the ratio Y can be determined by a relative measurement instead of two absolute measurements, so the G/T value obtained is more accurate. The correction factor K for the attenuation of the atmosphere is a function of the antenna elevation angle, the receiving frequency, the altitude of the antenna, the atmospheric temperature and density, and the humidity
The value of K used in equation (5) can be obtained from the curves shown in Figure 1, which show the variation of K with elevation angle under standard atmospheric conditions, when the main line is located on the horizon, and the frequency is the most commonly used frequency. Other factors are not considered because they have little effect on the accuracy of the G/T measurement. These factors include the fluctuation of the cosmic background radiation, the propagation loss and the influence of the earth station altitude. The correction factor K takes into account that radio stars cannot actually be treated as point sources, and the noise power received by the antenna from non-point source stars depends on the antenna beamwidth, which is given by the following formula. B(g,6)ds2
Formula: B(,)—brightness distribution of the radio source; P,0)—normalized antenna directivity diagram:
B(,0)P(g,6)d0
do=Sinodddo—differential of the solid angle in steradian, (,9)—spherical coordinate direction of the differential solid angle dα: 2.—stereoscopic viewing angle of the radio source in steradian. The correction factor K depends on the antenna beamwidth and the radio star. Figure 2 shows the relationship between the correction factor and the antenna half-power beamwidth for three radio stars. The analytical expressions of these curves are given in Appendix A. The power spectral flux density S in equation (5) depends not only on the selected radio star, but also on the frequency at which the G/T value is measured. The S value for each frequency of each radio star is given in Appendix A. 4.2 Selection of radio stars
When measuring the G/T value, the selection of the radio star depends mainly on the duration of time that the radio star can be seen from the position of the antenna. Usually stars move in circular orbits in the sky.
If the polar distance of the star (which is the complementary angle of declination) is lower than the latitude of the earth station, and the star and the earth station are in the same hemisphere (northern or southern hemisphere), then the entire orbit is above the horizon, and the minimum elevation angle (E) is at the "lower zenith". The Yamashita formula gives: E,-L+D- 90°
where 1) and L are as shown in Figure 3.
（7）
For other stars, only part of their orbit is above the horizon. Therefore, these stars will rise and fall. In this way, it is useful to calculate the angle above the horizon.
The maximum elevation angle (E) of any star is at the "upper zenith", and they have the following three cases; when the star and the earth station are in the same hemisphere, and 1)L, then: a.
E, = L + (90° - D)
When the star and the earth station are in the surrounding hemisphere, and D
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