lna bfr540

Hi, how do I select a suitable transistor for a wideband LNA with a bandwidth from 1GHz to 6GHz? Since the upper frequency is 6GHz, I assume the minimum transition frequency should be 12GHz. Is it necessary to do so? Do I need to select a transistor that is specifically made for wideband operation or any general purpose transistor will do? I have looked at several transistors from Phillips, Agilent and Siemens with transition frequency up to 25GHz. The Phillips BFG520, BFR520 and BFR540 for example are specified as a 9GHz wideband transistor, but the transition frequency is only 9GHz. While the Siemens SIEGET 25 BFP405 and BFP420 are not specified with any wideband operation, but they have transition frequency of 25GHz. So which one do I choose? Other transistors that I have seen is the Siemens BFP193W and BFP183W. Thank you.

Hi,
I advise you transistor SiGe from Infineon BFP640 with Ft=25GHz or BFG425w from Philips with the same cutoff frequency.
Those seem very good for your project because give a good GAIN a very small NF.
good luck

Hi,
we are using a BFP620 (Infineon). It has a very good noise figure and high gain even up to 12GHz. I have build several AMP with it, it's a good transistor.

Hi,
your choice is correlated about the NF and gain that u need (really IP3 could be important too). At the higher frequency band (6GHz for u), more gain u need higher the transition frequency must be.
Philips bjt, like BFG425W could be good (ft=25GHz),
but u could use BFU510 or BFU540 Philips too (ft=45GHz). The problem is that higher ft is, more difficult is to make a stable amplifier.
Another solution could be to use a two stage amplifier, using an easier bjt, with lower ft (ad example ft=12GHz) , more stable, playing on current supply for getting low NF at the first stage,
and more current at the second stage for getting the desired gain to add to first stage,
regards,
alex_vettoriale