Low Noise Amplifiers - Pushing the limits of low noise

Family of cryogenic LNAs (from L-band to W-band) developed and built for the VLA and GBT.

Program Overview

Cryogenic cooling of receivers to reduce their noise temperature is especially important in radio astronomy and in satellite and space communication.  An antenna is “looking up “ into the sky and, in the absence of strong celestial sources (Sun, Moon, planets, Cassiopeia, Cygnus, Taurus, Virgo, Orion, and the galactic plane) in the antenna beam, “sees” a very cold sky: 2.725 K of the cosmic microwave background radiation modified by the presence of atmosphere. The antenna temperature is therefore typically one order of magnitude or more less than in terrestrial applications (300 K). Consequently, a reduction of receiver noise by cryogenic cooling offers a very effective way of improving radio astronomy system sensitivity.

Since 1980, the Central Development Laboratory (CDL) has been a world leader in the development and production of Low Noise Amplifiers (LNAs) used at cryogenic temperatures for radio astronomy and deep space communication. Over this period the improvements made in the noise temperature of amplifiers have been quite dramatic. For example, in 1980, a noise temperature of 25 K was reported for a narrow band amplifier at the frequency of 4.5 GHz; in 2003, noise temperatures of 2 K, 8 K and 35 K were reported for broadband amplifiers at 4 GHz, 30 GHz and 100 GHz, respectively, at physical temperatures of about 15 K. These improvements have been central to scientific advancements. CDL not only provided LNA’s for all the EVLA, VLBA, GBT and NA ALMA receivers but also provided LNAs and/or shared the designs, assembly, and testing techniques with a number of other radio astronomy projects. Most importantly these include Wilkinson Microwave Anisotropy Probe, ESA PLANCK spacecraft Low Frequency Instrument, Cosmic Background Imager, Degree Angular Scale Interferometer, Arcminute Microkelvin Imager,  and NASA Deep Space Network, among others.

Historical Background:

In the early 1970s, ultra-low-noise receiving systems for deep space and radio astronomy employed mainly solid-state masers, cryogenically-cooled parametric amplifiers (or converters) and Schottky diode mixers. At the end of that decade, advances in Gallium Arsenide (GaAs) Field Effect Transistor (FET) technology made the noise performance of GaAs FET amplifiers competitive with the performance of parametric amplifiers. Additionally, a new mixing element, the Superconductor Insulator Superconductor (SIS) tunnel junction capable of almost quantum limited detection, was developed.

In the 1980s and 1990s, FET’s were gradually replaced by Heterostructure FETs (HFET), also known as High Electron Mobility Transistors (HEMT), of several different generations, first using AlGaAs/GaAs, then AlGaAs/InGaAs/GaA , and finally AlInAs/InGaAs/InP heterostructures. These last devices have become the technology of choice for low noise cryogenic amplifiers for frequencies up to W-band (3 mm). Quite recently a Silicon-Germanium (Si-Ge) Heterojunction Bipolar Transistors (HBTs) has been demonstrated to offer a competitive noise performance at cryogenic temperatures at low microwave frequencies (less ten 4 GHz). Such devices can be used in lower frequency amplifiers as well as in IF amplifiers for SIS mm-wave receivers, offering, in principle, an order of magnitude lower 1/f-like gain fluctuations, improving continuum radiometer sensitivity as compared with HFETs. SiGe HBTs are, however, not expected to compete with InP HFETs at higher microwave frequencies up to approximately 120 GHz. At these frequencies commonly known as W-band  HFET receivers now compete in noise performance with SIS/HFET mixer-preamplifiers. At frequencies above 120 GHz up to about 1 THz, SIS mixers demonstrate the best noise performance. Above 1 THz, cooled Schottky diode mixers and HEB mixers provide the lowest noise temperatures.

For more detailed historical review of the cryogenic amplifier work done at CDL please see: M. W. Pospieszalski, "Extremely Low-Noise Amplification with Cryogenic FET's and HFET's:  1970-2004," Microwave Magazine, vol. 6, no. 3, pp. 62-75, Sept. 2005.

Current Activities:

The research work and development work at CDL is centered on three main areas:

1.  Design, development and production of amplifiers for all NRAO radio telescopes in frequency range covering 200 MHz to 120 GHz.

2.  General noise properties of noisy networks, especially HFETs and HBTs at cryogenic temperatures.

3.  Radio astronomy receivers and radio meters employing HFETs and HBTs.

Inside of CDL W-band cryogenic LNA.

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Past Amplifier Group Accomplishments:

Papers

Cryogenic Amplifiers for Jansky Very Large Array Receivers

Ultra Low Noise Cryogenic Amplifiers