Low-noise RF Preamplifier
A low-noise 50-ohm broadband amplifier for early gain stages that functions at at a range or radio frequencies. Functions using the PHA-13LN+ (see parts list at bottom).
Project contribution by Lincoln Craven-Brightman, Research Engineer in the MR-PIGs group.
The LNA is housed inside a 0.75" X 0.5625" X 0.58" RF enclosure from Lotus Communications Systems (see parts list at bottom). The enclosure takes SMA input and output, and requires 6+ V DC with ~75 mA of operating current. The enclosure is connected to the board and SMA GND. The current model does not have impedance matching incorporated.
This layout is adapted from the PHA-13 datasheet from Mini Circuits.
The LNA demonstrates a gain of above 20 dB over 1-100 MHz. Gain slowly falls off to 17 dB at 1 GHz, and drops sharply below 1 MHz.
The enclosure is fitted with a crossed diode on the input to protect the pre-amplifier. Preliminary testing showed the circuit survived 200 Watts of transmit RF power (~5% duty cycle). With >1 KW of power, the PHA-13 was damaged and had to be replaced. The other components inside the enclosure survived.
The LNA was tested on the Halbach table-top scanner (~3 MHz center frequency) as a gain stage, along with the Minicircuits ZFL-500LN+ . It demonstrated similar SNR to the lab's current AU-1583 amplifiers when total gain was comparable, using different gain stages. The domain chosen as "noise" is delimited by vertical dashed lines. All testing data is included below.