Matching NRF24L01 to unusual antenna (40+j48)

[Janis]

Hi!

I must match NRF24L01 to 40+j48 ohm antenna. This is not my design, so no possibility to change. I have PCB antenna, that was measured to be 40+j48 inside enclosure.

So I have some questions:

1. Is it correct to assume 15-j88 ohm port (ANT1-ANT2) impedance? Noting that datasheet states best power in 15+j88 load (so taking conjugate).

2. Also I can't get 50 ohm impedance at matching network output for reference design, no matter how I calculate it. I've tried to get it looking from side of antenna, calculated all impedances at 2.5GHz, then merged them and got 7.64-j52. Using spice I got 7.4-j51 So the question would be if someone could show how it actually transforms amplifiers 15-j88 to loads 50? Maybe its wrong to substitute port impedance that way, is there some catch?

[Håkon Alseth]

Hi,

That is not going to be an easy task. Our radio's uses a reference matching network w/50 ohm single ended output. This also includes a high-order filter to suppress harmonics and spurious. Changing this output impedance is going to give you a head-ache in terms of teleregulatory compliances (FCC/ETSI etc) and performance.

A better approach will be: What I suggest that you do is to insert a PI-network to tune your antenna into 50 ohms using a network analyzer.

Best regards Håkon