The Harmonic Interference Problem of LO in Delingha mm Wave Telescope

In radio astronomy, the problem of RFI (Radio Frequency Interference) is various and complex. In the face of different RFI problems and interference mechanisms, the pertinent methods are adopted. The RFI mitigation at the device stage can prevent RFI from entering the telescope. A 9-beam sideband separation superconducting receiver for Delingha millimeter-wave telescope is introduced. 18 LO (Local Oscillator) signals are allocated by a LO chain system. Aiming at the IF (Intermediate Frequency) narrowband interference caused by the harmonic signal of the signal generator in the LO chain, a test scheme of injecting simulated harmonic signal is designed. The interference mechanism, the correspondence between the frequency and power of interference signal and the frequency of harmonic signal are confirmed. The transmission path of harmonic interference is analyzed and verified. In order to mitigate harmonic interference, the YIG filter with band-pass characteristic of variable frequency band is used to filter out harmonic signal in the LO chain system. The harmonic signal is prevented from coupling into the receiver system and the mitigation of harmonic interference is completed.