PCB antenna impedance

RE: PCB antenna impedance

wiki — Tue, 06 Jan 2015 01:06:58 GMT

Thank you ! Happy new year !

RE: PCB antenna impedance

Asbjørn — Fri, 02 Jan 2015 18:34:12 GMT

Please see the two following white papers. The first one is for tuning the matching network and will give you information on what the matching network is and what it does. For the most part, this is what you have inside the red rectangle. Although you are using the nRF51 and not the nRF24Lxx, the component values are different, but principal is the same.

Second one is on the topic of antenna tuning. For your layout above you are using a PCB antenna and have one antenna tuning component, the C5 (I believe).

The Q value is important, but as long as you use components intended for 2.4 GHz RF with self resonance frequency well above 2.4 GHz you should be fine. For example, we use components from the Murata LQP15 series here.

The output power loss is dependent on how it's working already. That doesn't mean that you will see increase/decrease from tuning it. We recommend customers to test and verify. If it's low, you will probably see some benefit from tuning it. But measure the output power conducted and tune it with component values instead of measuring the impedance between the different components.

RE: PCB antenna impedance

wiki — Fri, 19 Dec 2014 09:08:43 GMT

Hi Asbjørn

I have some confusion . For the red square ,is it nacessary that the Q value of L1、L2 and L3 should to be considered ? Is it right that if we do not match the red square ,the outpower loss will increase .

RE: PCB antenna impedance

wiki — Fri, 05 Dec 2014 03:27:23 GMT

Ok . Thank you so much !

RE: PCB antenna impedance

Asbjørn — Thu, 04 Dec 2014 14:16:41 GMT

No, the impedance will be 50 Ohm at the output of the matching network for the radio. I believe that would be at the intersection of L3 and C6. Then C5 is used for tuning the antenna input impedance seen from L3 and C6 into 50 Ohm. You check this during development by confirming that the output power is good or the range is fine. You shouldn't need to check this in production.

Also, the impedance inside the red square won't be 100 Ohm, it will be unknown at the different locations. The only place you know you'll have a known impedance is the 50 Ohm place between L3, C6 and C5.