As RFI situation below 30GHz becomes increasingly crowded, a need for a preselector filter in front of LNAs in receivers for radio-astronomy urges. However, any losses and thus noise contributed by such filter would have large impact on the overall system performance, as they are in front of the first amplification stage.

A filter made of a superconducting material provides necessary filtering characteristics with very low losses and contributing nearly no noise. Thus, allows for a filter with very high order filtering providing also great flexibility with regards to transfer characteristics, allowing for instance multi-band operation with only certain RFI intense bands blocked.

On the other hand, the specific properties of superconducting filters can cause following LNA to fall into instability. In addition, development, characterization and operation of such filters is challenging as it is not possible to operate or measure them outside of cryogenic environment. Furthermore, in case they are to be used in phased array systems, a reliable and relatively cheap method to produce hundreds of such is necessary. Current progress in research and development on a superconducting preselector filter for radio-astronomy applications at MPIfR will be presented.