Antenna tuning with chipset antenna

[vidal]

Hello,

I developed a Nordic board with 2450AT18B100 chipset antenna. I follow the design of Solar Powered Sensor Beacon.

infocenter.nordicsemi.com/index.jsp I test it and it works fine, but I want to tuning the antenna in order to get minimum return lose in signal.

So, I implement this antenna circuit in my board.

From johanson technology values are:

I suppose that from C3 and L1 you have to modify some references values of johanson chip antenna.

In general, my questions are:

Can you explain me each part of this circuit?.

Can you explain me why do you change this values and how do you calculated?.

Can you explain me how tuning the antenna?. Because your reference document for that do not explain how to do it in this case.

infocenter.nordicsemi.com/.../nwp_017.pdf

Thanks in advance.

Jose.

Others attached files. Conductor Impedance

Trace Lenght Solar Beacon

[FormerMember]

Impedance/output power of the chip: There are two ways to verify that the impedance is approximately 50 Ohm:

Measure output power: If you have followed (copied) the reference layout, it should normally not be necessary to modify the values of C3 and L1. You can verify that the impedance is correct (50 Ohm) by measuring the output power using a spectrum analyzer. If the measured output power is the same as what it was set to be, the impedance is 50 Ohm.

NB: Remember to measure the signal level of the harmonics and the frequency of 2xRX LO (center frequency 4.88 GHz) as well.

Measure the impedance: A vector network analyzer (VNA) can be used to measure the impedance of the chip. Connect the VNA "to the chip" after C3 and L1, set the radio in nRF52832 in RX or TX mode, and measure the impedance. The impedance should be approximately 50 Ohm.

Tuning of the antenna: To tune the antenna, a VNA should be connected to the antenna, by connecting it right before the matching network, the order will be the following: VNA connected - matching network - antenna. The connection towards C3/L1 should be cut of, see picture below.

When the VNA is connected, you should change the values in the matching network until the measured impedance is as close to 50 Ohm as possible across the band. Use the smith chart to get an approximation of the values for the matching network. Start with the components closest to the antenna.

Typically, chip antennas are quite narrow banded. We usually say that if the measured SWR is below 2 across the band, the antenna is well tuned.

As initial values, when doing the tuning, I would recommend the following: C13 and L5 is 0 Ohm, and L4 is not mounted.