A High-Order L-Band HTS Filter for Sensitive Detecting

In this paper, a new high-temperature superconducting (HTS)-based microwave radiometer with an improved sensitivity is presented. The cryogenic receiver front end consists of an HTS filter and a cryogenic low noise amplifier (LNA). The cryogenic receiver front end shows an ultra-low noise figure and can suppress radio frequency interference (RFI) effectively. The proposed HTS filter works at a center frequency of 1.4135 GHz with a bandwidth of 25 MHz. The measured mid-band insertion loss, side band steepness, and out-of-band attenuation of the HTS filter are 0.14 dB, 35 dB/MHz, and 80 dB, respectively. The noise figure of the cryogenic LNA is about 0.27 dB at a temperature of 77 K. Compared with other total power radiometers, the proposed radiometer has a lower receiver noise temperature, which can improve the sensitivity with a short integration time of the satellite-based salinity meter. In addition, since the bandwidth of the salinity meter is fixed and the integration time of satellite-based equipment is limited, such a low receiver noise temperature can increase the flexibility of future satellite payload configuration program.