Resistor tolerance and requirement for RF matching network

[floatcloud]

For NRF51 and NRF52 antenna matching network, is there any requirements for resitors? Tolerance? 

I know there are some requirement for capcitor and inductor types, how about resitors?

Can I use regular 0402 resistor with 1% tolerance for tunning?

[haakonsh]

Hey floatcloud,

Yes, NP0!

You can use any 0402 1% NP0 components. You should never use any other resistor than 0ohm resistor, and only as a bridging component or as a cheaper alternative to a 1nH inductor. 

Cheers,

Håkon.

[floatcloud]

Hi haakonsh, thank for the reply,

Could you explain a little bit why a resistor other than 0ohm should never be used?

The reason why I ask this is that, in one of our boards, I tried using a single 24ohm resitor as the bridging component without any shunt component for antenna tunning, resulting the desired frequency right at the bullseye of the smith chart. 

The same goal wil be more complicated to achieve if using only capacitors and inductors.

What do you think of that?

thanks

[haakonsh]

An impedance with a real component larger than zero will burn energy that would otherwise get transferred to the antenna.

The ideal impedance match is 50ohm, but it is a complex value where the resistive component is zero and the reactive component is 50ohm; Z = 0R + 50i ohm. 

 

[floatcloud]

thanks for the clarification