LNA and RF switch positioning


We are designing a new multi-antenna RF system, in which 6 antennas are connected to an RF switch (a SP8T) itself connected to a SDR. We ask ourselves where to put a LNA: between the antennas and the RF switch (1 LNA per antenna, so 6 at all), or between the RF switch and the SDR? The first solution seems better according to the law of Friis, but it is much more complicated (integration, power supply ...).

Do you have any advice on this?
  • +1
    •  Analog Employees 
    on Sep 2, 2019 7:28 PM


    This depends on your system requirements. I suggest you to calculate or simulate your system performance for both configurations.

    The location (before or after switch) of the LNA will mainly affect the  I system noise figure. You could consider using a single LNA at RFC port of switch if the noise figure requirement of your system is met.