Conversion of Line Polarization to Circular Polarization in L Band Receiver of 26m Telescope in Xinjiang Astronomical Observatory

The L-band receiver can be used for pulsar observation, molecular line observation and international VLBI joint-observations of the 26-meter telescope at Nanshan in Xinjiang Astronomical Observatory, Chinese Academy of Sciences. The L-band receiver is mainly developed for pulsar observations, which outputs linear polarization signals. Circular polarization signals are required in molecular line observation and the international VLBI joint observations. We hope that the L-band receiver can be used for both linear polarization signal observation and circular polarization signal observation, so a polarization conversion device is used to convert the linearly polarized signal to the circularly polarized signal in the L-band receiver. The isolation between right-hand circular polarization signal and left-hand circular polarization signal must be large enough in the converting process. In this paper, a 90° Hybrid Coupler is used and its role in the conversion is studied, and the converting method is realized. The isolation of the two circular polarization signals meets the requirements of the subjects, both types of signals can be used in circular polarization observation.