Chip Antenna

[Mikebits]

Anyone know much about chip antennas? I have a couple questions. First question, Has anyone used chip antennas, PCB trace antennas, or both? Which one would you suggest going with. I am leaning towards the chip antenna as I think it would simpler to design into a circuit.

Second question I have is what is the purpose of the trace connected to pin2 of the chip antenna. The pin is not connected internally to the chip, so what the heck does the trace do? See image.

 

[MikeMl]

Is it possible that the "chip" is nothing but distributed inductance that brings the trace on the right to resonance? (Inductively-Loaded whip antenna).

ps, post what you learn. I'm curious.

 

[JimB]

Mikebits, can you post a link to the original datasheet for this thing?
JimB

 

[Mikebits]

Here is the full data sheet. https://www.mouser.com/ds/2/611/0868AT43A0020-242305.pdf
I have one of the parts and measured it with a ohm meter and it is not connected, like an inductor anyways.

 

[MikeMl]

Read this.

 

[Mikebits]

That page does not even show the stub. I think I will contact the Apps support people at JT.

 

[JimB]

Having had a look through the Johanson website, the only reference I can see to an antenna with the "extended track" is a photo of some typical example. I cannot find any technical information on this configuration.

JimB

 

[alec_t]

Interesting that the second pic shows pin 2 as 'NC', whereas the third pic shows pin 2 connected to a trace (counterpoise?)

 

[RadioRon]

The NC description for pin 2 is very misleading. This pin is coupled to the internals of the antenna chip whether you like it or not just by virtue of being so close to the conductors inside the chip, so while it may be a DC "no-connect" its still coupled at RF frequencies. My guess about the added stub is that it is primarily there to tune the resonant frequency of the antenna down to the 878 MHz region. It does this by adding extra length to the overall monopole structure, making it electrically longer. Radiation comes from current, and in this configuration, the peak current is likely still near the base (pin 1) of the antenna chip and so the added stub probably isn't changing the radiation pattern all that much.

It is interesting that the tip of the stub is folded back to lie beside the hottest part of the chip radiator, as if to intentionally couple across. This may have some interesting effects on the input impedance, albiet minor, but without simulating this design, its hard to tell exactly how.

It is worth mentioning that the chip is meant to be the radiating element of a monopole antenna. Therefore, it relies on the associated "ground plane" to form the counterpoise. Without this ground plane, radiation would be bad, falling well short of expectations, and input impedance would also be bad. The groundplane is really the "other half" of the dipole.

 

[Mikebits]

Thanks Ron, Good explanation. Having to add the stub seems to defeat the purpose of using a chip antenna. Other manufacturers do not require a stub. I wonder what the performance difference is.

 

[RadioRon]

You make a good point, Mike. Overall its still well short of the 60 mm it would take to make a monopole using only a pcb trace, but you're not getting full value for that chip, I agree. There are many other manufacturers out there to choose from, but I see that the Johanson ones are well priced in comparison.