A 75-ohm Uncooled L-band Low-noise Amplifier for FAST Core Array

The proposed FAST Core Array, a key future upgrade for the Five-hundred-meter Aperture Spherical radio Telescope (FAST), requires highly sensitive yet cost-effective uncooled receivers. This paper presents the design, fabrication, and characterization of an uncooled 75-ohm low-noise amplifier (LNA) for the array’s L-band receiver, operating across the band of 1–1.8 GHz. By utilizing an ultra-low-noise indium phosphide pseudomorphic high-electron-mobility transistor (InP pHEMT) and a novel low-loss suspended substrate line for the input matching network, the prototype achieves a gain of approximately 39 dB and a lowest noise temperature of 7.6 K, with input and output return losses better than –8 dB and –15 dB, respectively. The receiver noise temperature was measured as low as 20 K in the 1.6-1.8 GHz sub-band, using the Y-factor method, with the cold sky as the cold load and a room-temperature absorber as the hot load. These results validate the practical viability of the proposed uncooled receiver architecture and demonstrate the feasibility of employing high-performance uncooled LNAs to meet the stringent sensitivity and reliability requirements of the next-generation FAST Core Array.