1. Existing problems on switching between C band linear and circular polarization
(1) Generally, under the status of linear polarization, cross polarization of transmitting and receiving frequency is 90º±0.5º, but now it is 90º±2º or 90º±3º. Obviously, cross polarization of transmitting-receiving frequency could not reach the best state at the same time. The reasons are as follows. There is no strict tolerance requirement on the screw-connected holes of the polarizer or duplexer, or although there is tolerance requirement, the processor fails to follow it during processing. Therefore, the original drawing needs reviewing or revising again.
(2) When online system for the duplexer is installed, the deviation between the duplexer and the center line of the corrugated horn with circular waveguide connected by the duplexer should be kept as small as possible. Therefore, it is better to use pins for positioning when flanges are connected.
(3) During the test of cross polarization, change the antenna’s azimuthal angle and pitching angle and find minimum signal level, and then rotate polarization of the duplexer and find maximum signal level. The electrical level fluctuation caused by tolerance of angle is : A=20㏒sinθ. For example, if θ=90º or 80º, A=0dB or -0.13dB respectively and tolerance is ±10º. However, in the cross polarization, if θ=1º, A=-35dB and the requirement is met. If θ=2º, A=-29dB and the requirement is not met. It can be seen that θ≤1º.
Therefore, during debugging of cross polarization, rotate polarization and find minimum signal level. Then change the antenna’s azimuthal angle and pitching angle and find minimum signal level. Repeat these steps several times and then minimum signal level could be found.
2. Procedure for debugging the duplexer of C band linear and circular polarization
(1) Mark linear polarization. Rotate position of the duplexer against the circular polarizer and find minimum signal level. Mark the angle of linear polarization, where it is the position of minimum point for cross polarization. (Debugging is carried out on transmitting frequency and receiving frequency respectively.) Rotate the polarizer by 90º, where it is the position of co-polarization.
(2) At the position of cross polarization, rotate the polarizer by ±45º, which could be determined as the angle of levorotatory and dextrorotatory circular polarization.
(3) Complete debugging procedure first in the laboratory, and then complete debugging procedure by simulating the construction site after installation on the antenna.