  The growing number of phased array feeds (PAF) being built for radio
astronomy demonstrates an increasing need for low noise amplifiers (LNA) that
are designed for repeatability, low noise, and ease of manufacture. Specific
design features which help to achieve these goals include the use of unpackaged
transistors (for cryogenic operation), single-polarity biasing, straight
plug-in RF interfaces to facilitate installation and re-work, and the use of
off-the shelf components. The focal L-band array for the Green Bank Telescope
(FLAG) is a cooperative effort by Brigham Young University (BYU) and the
National Radio Astronomy Observatory (NRAO) using warm dipole antennae and
cryogenic Silicon Germanium Heterojunction Bipolar Transistor (SiGe HBT) LNAs.
These LNAs have an in band gain average of 38 dB and 4.85 Kelvin average noise
temperature. Although the FLAG instrument was the driving instrument behind
this development, most of the key features of the design and the advantages
they offer apply broadly to other array feeds, including independent-beam and
phased, and for many antenna types such as horn, dipole, Vivaldi,
connected-bowtie, etc. This paper will focus on the unique requirements array
feeds have for low noise amplifiers and how amplifier manufacturing can
accommodate these needs.
