Ultralow-Noise Microwave Amplification
Our uncooled amplifier device is now world's lowest noise. It achieves 3 K noise temperature at 1.4 GHz frequency, for example. Conventional amplifiers must be cooled to 20 K physical temperature to achieve this level of performance. In addition, this device provides the same low noise temperature when operated as an active cold load.
The primary interest is for next-generation radio telescopes requiring ultimate receiver sensitivity, such as the future Square Kilometer Array or China's Five-hundred-meter Aperture Spherical Telescope.
Multibeam Feed
Arecibo 7-element L-band multibeam feed.
The Arecibo Observatory 7-element multibeam feed pictured at right uses conventional amplifiers that require cooling. The entire lower half section of this structure containing 14 amplifiers for dual polarization must be enclosed, evacuated, and cooled. An upgrade to uncooled amplification eliminates the cost and complexity of cryogenic cooling, with greater reliability and less down time.
China Five-hundred-meter Aperture Spherical Telescope (FAST)
New multibeam feed designs can take advantage of uncooled simplicity, lower weight, and lower cost to put more beams on the sky at no sacrifice in noise performance. A 19-element L-band feed is proposed for China's Five-hundred-meter Aperture Spherical Telescope (FAST). This reflector system design places the feed in the reflector edge plane for very low ground noise contribution. Using uncooled 3 K amplifiers, we expect 10 K system noise can be realized—half the value of other reflector telescopes and a huge sensitivity advantage. Moreover, multibeam capability is easily added to other bands in the FAST feed array. Indeed, this amplifier technology can enable future focal plane array feeds of 100 elements or more now hindered by high noise temperature.
China's Five-hundred-meter Aperture Spherical Telescope completed construction in 2016.
At left, FAST beam pointing is by movement of the feed station with a cabling system, all located 140 meters above the fixed reflector surface. Feed station weight reduction obtained from uncooled amplification is a significant design advantage in the control and stability of the feed positioning system.
International Square Kilometer Array (SKA) Radio Telescope
The most extensive Mid-Frequency Aperture Array (MFAA) portion of SKA pictured below is scheduled to begin construction in 2023. It is planned to comprise 250 stations, each 56 meters in diameter, and total 55 million active receiving elements in the 0.4- to 1.4-GHz band. Since receiver cooling is not feasible in this case, weak signal detection sensitivity is critically dependent on uncooled amplifier noise performance. The MFAA design goal is 40 K system noise in order to meet system sensitivity (Aeff /Tsys) requirements.
Artist's impression of MFAA stations. Credit: SKA Organisation
Our 3 K uncooled amplifiers and integrated antenna element design can realize 10 K system noise temperature and easily meet MFAA requirements. Moreover, 10 K system noise allows 75% array size reduction for equal system sensitivity, and this fact has tremendous implications for both construction and long-term operating costs. We estimate the total cost of construction to be $2 billion. Therefore, $1.5 billion can be saved utilizing our amplifier technology. In addition, energy cost savings would be $40 million per year, as the estimated annual energy cost to operate MFAA is now over $50 million. Alternatively, if full array size is maintained, then system sensitivity is increased four-fold over the baseline design. This provides a 16x increase in survey speed, the rate at which observational data is collected by the instrument.
Perhaps the most significant consideration in favor of ultralow-noise amplifier technology is overall project risk. Nearly twenty years ago, the Allen Telescope Array project chose to build a high-noise (45 K) system, and today, that array construction is only 12% complete. MFAA is to have 100 times the collecting area of the original Allen Telescope Array. Therefore, it would be a serious mistake to proceed with building a high-noise system that potentially places MFAA on a path similar to ATA. nn
