FMCW Radar - How to choose the right LNA?

[mehmetkacmaz]

I'm working on a FMCW Radar design and I had struggled a bit with gain problems.

My main problem is that after VCO (Voltage controller oscillator) I need to connect an LNA (Low noise amplifier) to the circuit to increase power before goes to TX antenna. At this point, after the LNA to be selected, the power will be divided into two with the wilkinson divider and some of it will go to the TX antenna. But I don't know how many db this power value should be increased. How can I learn this?

Thanks.

 

[BradtheRad]

Volt decibels use a different formula from Watt decibels. Something to do with 10 versus 20.

Determine whether it's Volts or Amperes that changes, and results in power changing ('divided in two').

The transmitter needs a certain volt level, at a certain amount of Amps.

 

[G4BCH]

How much transmit power do you need? How much power does your VCO give?
Work out both those quantities in dBm ( 10*log10(power in mW) )subtract VCO power from the transmit power and that gives you the gain you need in dB.
If you are making a radar or want to work in RF and do not know what dB means you need to learn or you will not get anywhere.