Abstract
This article describes a low noise amplifier which is believed will have a transformative impact because of the following characteristics: 1) the noise temperature at a physical temperature of 25 °C is a factor of 4 lower than typical commercial LNAs; 2) the noise decreases to 4.5 K at a temperature of -40 °C, a temperature realizable with solid-state coolers; 3) the LNA has an integrated, extremely stable noise source to facilitate measurement of system noise temperature; and 4) the amplifier is powered by a dc voltage and controlled by a tone signal on the RF output cable thus requiring no additional wiring. The amplifier benefits systems in the low microwave frequency range with low background temperature, such as those for space communications and radio astronomy, but without the capital and maintenance costs of cryogenic systems. This article describes the construction and test results with an emphasis on the manufacturability and accuracy of the noise measurements. Finally, the noise of a system deploying the LNA is described.
Highlights
T HE topic of this article is a low noise amplifier operating at ambient temperatures with an exceptional noise temperature of 7 K at 1.4 GHz
The amplifier performance exceeds that of early cryogenic amplifiers introduced by one of the authors 40 years ago [1] and with solid state cooling to −40 ◦C has comparable noise to more recent cryogenic amplifiers [2] at frequencies below 2 GHz
It is important to note that all resistances in the HEMT model represent thermal noise at ambient temperature except the drain-to-source resistance which is at a high temperature, Tdrain, to represent the hot-electron noise
Summary
T HE topic of this article is a low noise amplifier operating at ambient temperatures with an exceptional noise temperature of 7 K at 1.4 GHz. The amplifier has application in receiving systems where the background noise temperature, Tb, is low, of the order of 10 K, as is the case when the LNA is connected to a low-loss antenna with a beam pointed at the cold sky [2]. This occurs for satellite communications and radio astronomy but not for terrestrial communications where Tb ∼ 300 K.
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