The low noise amplifier is designed to have a minimum noise figure capable of capturing the SDARS signal. The LNA also amplifies the signal to a level to be processed by the tuner. The noise figure is important since it sets the parameter of how well the whole front-end receiver captures the attenuated signal. Three stages were identified and designed for the LNA; one for lowest noise figure and two for gain.

Based on information from the commercially available antenna, specifications needed to receive the SIRIUS radio signal were identified: a minimum noise figure of .7dB and a gain in the range of 28.5 to 32.5 dB. After doing some tests in the commercially available unit (TRK-SR20S antenna) from TERK technologies it was proved that it was possible to receive the SIRIUS signal with a noise figure of 1.5dB and a gain of 40dB. After analysis the decision to design under the test value specifications was made.

The MGA-71543 transistor from Agilent technologies is used since it has the appropriate specifications needed at the frequency range of our project (2.32-2.3325GHz). Design techniques for input and matching networks for the transistors were implemented to avoid any gain losses of signal between stages. Appropriate choke and resistor-bias networks were designed to ensure accurate performance of the transistors in the three stages. The first stage provides the low noise figure for the whole LNA. From the formula below it shows that the first stage is the dominant determining the noise figure.

F is the noise figure of the amplifier in dB
G is the gain of the amplifier in dB

The other two stages are designed to provide a gain that will complement the first stage for an overall gain in the range of 28.5 to 32.5 dB. The need for a voltage divider circuitry is also added to deliver appropriate biasing voltage and current to the transistors. The technique to fabricate the LNA was determined to use surface mount lumped components for the matching, choke and biasing networks interconnected with 50 Ohm transmission lines.