How to use the 1.5m antenna to simultaneously receive C and Ku-band satellite TV programs on satellites is an issue that is hard to explore for many satellite TV receivers. The following data is given from the principle, I hope to have something for everyone. help.
The main parameters of the antenna are mainly represented by the diameter D of the antenna, the operating wavelength λ, the efficiency η, the gain G, and the like. The relationship between them is represented by the following formula:
G(Db)=10lg[η(Лd/λ)2]............1
The operating wavelength of C-band λc=0.076m (center frequency), take η=0.6 (generally 0.5~0.7), substitute 1 to get:
Gc=10lg[0.6(3.14&TImes;1.5/0.076) 2]=34(Db)
The focal length of the 1.5 m antenna is f = 0.58 m, and the focal length aperture ratio is f/D = 0.58 / 1.5 = 0.39. From the parabolic equation X2=4fZ (only X plane), the feed angle ∮C=140° (also the width at 10dB of the C-band feed beam) can be calculated, where X is the parabolic trajectory, f is the focal length, and Z is the rotation. The corresponding size of the shaft, as shown in Figure 1.
Since the Ku-band tuner (with feed) on the market has a width of 68° at the feed beam of 10° (the E and H faces are different), the actual antenna aperture is used on the above specific 1.5 m antenna. For 0.75m, in order to increase the actual use area of ​​the Ku antenna, increase its gain, and reduce the mutual influence between the C and Ku-band feeds, the Ku-band feed can be processed into the shape of Figure 2.
The width of the Ku-band feed beam after processing is increased from about 68° to about 80° (that is, the feed angle), so that the diameter D of the reflector used can be obtained from the original 0.75m. Increase to 0.9m, the operating wavelength of Ku-band λKu=0.024m (center frequency), substitute D and λKu into equation 1, and its gain Gku=10lg[0.6(3.14&TImes;0.9/0.024 ) 2] = 0.392 (Db)
The opening angle of the antenna beam half power point can be calculated by the following formula: 2Q3dB=1.26λ/D&TImes; 57°...............2
Then 2Q3dBC=1.26(0.076/1.5)&TImes;57°=3.6°
2Q3dBKu=1.26(0.024/0.9)×57°=1.9°
If we place the C-band feed phase center on the focal point F of the parabolic antenna, the antenna beam's maximum pointing is consistent with the antenna axis, so that the Ku antenna can receive an angle (such as 5°) from the antenna axis. In the Ku-band TV program on the satellite, the feed phase center of the Ku antenna must deviate from the antenna axis, pass a point B on the line perpendicular to the axis, and the incident angle to the apex of the reflector is set to ∮, and the reflection angle is ∮ ', they have the following relationship, ∮ ' / ∮ = 0.95, because we need ∮ ' = 5 ° (that is, the angular difference between the two satellites with a longitude difference of 5 ° received) so ∮ = ∮ ' /0.95=5°/0.95=5.26°
Therefore, the distance between point B and point F can be obtained from tg5.26°=FB/F=0.092, FB=0.092F=0.092×580=53(mm), related to C and Ku bands. The parameters can be represented by Figure 3 (not to scale).
Since the Ku-band phase center is 53mm, the gain will be reduced from 39.2dB to 38.7dB, the beam will be wider, and the 2Q3dBKu will be increased from the original 1.9° to 2.1°. The Ku-band program on E-Palapa and 116°E Hanxing-3 satellites, the antenna gain at 2QKu=3° is calculated, and the gain at 3° beam is 38.7dB-4.3dB=34.4dB. ,acceptable. That is, the maximum direction of the Ku band is directed (113°+116°)/2=114.5°. The maximum pointing of the C-band antenna beam will point to 114.5°-5°=109.5°, and the Xinnuo No.1 with its beam pointing at 110.5°E is only 1° out of phase, which is only lower than the original maximum gain of 34dB. About 1dB.
In order to meet the FB=53mm requirement, a circular hole should be machined in the appropriate position of the ∮130mm disc in the C-band feed to allow the Ku-band feed to be loaded, as shown in Figure 4. The assembly drawing after processing of C and Ku band feed is shown in Fig. 5. After the above changes, you can choose to receive TV programs from the following two satellites:
1. Received 100.5°E Asia 2 C-band program while receiving 105.5°E Asia 3S Ku-band program. The reverse is also true, but the C-band feed ∮130mm disc (with the Ku-band feed) needs to be rotated 180° to move the Ku-band feed to the other side.
2. Received 105.5°E Asian 3S C-band program, and received the 110.5°E Xinnuo No.1 Ku-band program. The reverse is also true, the method is the same as above.
3. Received the C-band program on the 110.5°E Xinnuo No.1, and received the 113°E palapa and the 116°E Hanxing 3 Ku-band program.
With the continuous development of the satellite TV industry, the density of satellites will continue to increase. It is theoretically and practically realistic to use an antenna to simultaneously receive antennas of multiple satellite programs. For example, if two circular holes are symmetrically machined on a disc of a C-band feed, and a Ku-band feed is installed, can it not simultaneously receive more Ku-band programs on another satellite?
prompt:
1. During installation, the polarization directions and polarization deflection angles of the C and Ku bands must be the same, and the C-band is required to ensure that the phase center of the C-band is placed on the focal point F and the maximum beam pointing is aligned with the antenna axis. The circumference of the 130mm disc is the shortest distance from the antenna reflector (the appropriate point can be measured), and the distance of the ∮63mm cylinder from the disc is about the same (about 5mm), which can not be installed obliquely. .
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