What this transistor brings to the RF front end
The Infineon BFP842ESDH6327XTSA1 is a silicon-germanium (SiGe) NPN RF transistor designed for low-noise amplifier stages up to C-band and X-band frequencies. Its headline specs — a transition frequency of 60 GHz, a noise figure of 0.65 dB at 3.5 GHz, and a gain of 26 dB — make it a natural fit for the first LNA after the antenna filter in base stations, satellite downconverters, and 5G small-cell receivers. The 3.7 V collector-emitter breakdown means this part runs from a 3.3 V or 3.6 V rail, not a 5 V or 12 V supply, so check your bias network before dropping it into a legacy design.
Noise figure and gain — the pair that matters
At 3.5 GHz the BFP842ESDH6327XTSA1 delivers a noise figure of 0.65 dB and a gain of 26 dB. That noise figure is the number that decides whether this transistor earns its place in a receiver chain: every tenth of a dB you save at the LNA directly improves the system noise floor. The 26 dB gain means a single stage can lift a weak signal enough to drive a mixer or a second gain block without an extra buffer. If your design targets a lower band — say 1.8 GHz or 900 MHz — the noise figure will be even better, though the datasheet only specifies it at 3.5 GHz.
Package and footprint — SOT-343 realities
The part comes in a standard SC-82A / SOT-343 package, supplier code PG-SOT343-4-2. That is a four-pin, surface-mount package with a small collector pad underneath — the centre pad is the collector, not a thermal slug, so your PCB footprint should follow the Infineon recommended land pattern for SOT-343. The package is rated for a junction temperature of 150 °C, which gives decent headroom for LNA stages that run warm.
Sourcing this part — what to expect
If you are cross-shopping, the BFP640FH6327XTSA1 is a close functional sibling: same SOT-343 package, 40 GHz fT, 23 dB gain, and a noise figure that ranges from 0.65 dB to 1.2 dB across 1.8 GHz to 6 GHz. The BFP842 gives you higher fT and more gain, so it is the better pick for designs that push past 6 GHz or need extra stage margin.