Design for a Superconducting Filter Front-End

We propose a front-end with a combination of a circulator and receive and transmit superconducting filters (SCFs) for applications to the base stations of the future generation wireless communications. Ideally, all superconducting filters used are desirable. We made and estimated a preliminary front-end model with a volume of 43 liters using a duplexer, superconducting filters, and a cryo low noise amplifier (LNA), etc. for 5GHz band recently. In the preliminary model, noise figure (NF) had 2.0 dB or lower, and the transmit SCF endured over 10W. The measured normal duplexer showed that between the receive and transmit channels with 100MHz bandedge separation was isolated to be 30dB, which is not enough for practical use. It was found that the combination of a circulator and receive and transmit SCFs can improved the isolation to 80dB or more. Besides, we designed a new compact front-end that reduce the volume to the target value of 15 liters. To reduce the volume, the cryo-cooler and the dewar with a vacuum chamber, and other RF components needs to be miniaturized. Therefore, we selected the circulator instead of the duplexer.