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RFI mitigation at a 2GHz band by using a wide-band high-temperature superconductor filter
Eiji Kawai, Kashima Space Research Center, NICT
Junichi Nakajima, Kashima Space Research Center, NICT
Hiroshi Takeuchi, Kashima Space Research Center, NICT
Hiromitsu Kuboki, Kashima Space Research Center, NICT
Tetsuro Kondo, Kashima Space Research Center, NICT

Severe radio frequency interferences (RFIs) at an S-band (2GHz) due to third-generation mobile phone system (IMT-2000) have started since 2002 at a 34-m antenna located at the Kashima Space Research Center, National Institute of Information and Communications Technology (NICT : former Communications Research Laboratory) in Japan. It was difficult to continue observations at the S-band due to the saturation of the downconverter by RFI signals.

To mitigate RFIs, a new High-Temperature Superconductor (HTS) band-pass filter was developed in cooperation with DENSO CORPORATION Research Laboratories. The HTS filter has superior characteristics as follows; sharp frequency cut-off, wide bandwidth, and low losses. Since an LNA of the S-band receiver was not saturated, we installed the filter to the LNA output to avoid the unnecessary increase of system temperature.

Consequently we could mitigate RFIs and observations at the S-band becomes possible again. Even though RFIs become stronger than the present situation and the saturation of LNA occurs, we can install the HTS filter in front of the LNA because of its low losses.