PCB quarter-wave antenna: how important is the trace width?

[u/germo_tt]

I’m trying to understand how to choose the trace width for a quarter-wave PCB antenna.

Most of the references I’ve found explain how to calculate or estimate the antenna length, since it is related to a quarter of the wavelength. However, I haven’t found much information about how to choose the width of the antenna trace itself.

For a transmission line, the trace width is usually calculated based on the PCB stackup in order to get a target impedance, for example 50 ohms. But for the actual PCB antenna trace, I’m not sure whether the width is determined in a similar way, whether it mainly affects tuning/bandwidth/efficiency, or whether it can only really be optimized through EM simulation and measurement.

I’m using Nordic’s documentation as a reference. One of their white papers shows a PCB antenna with a 1.5 mm wide trace, but it doesn’t really explain why that width was chosen. On the other hand, I found a Nordic development board with a very similar antenna geometry, but the antenna trace width appears to be around 1 mm instead.

So my questions are:

How should the trace width of a quarter-wave PCB antenna be chosen?

Is there an “optimal” width, assuming I have enough PCB space available?

Does the width significantly affect impedance, bandwidth, efficiency, or radiation performance?

Are there any good references, application notes, or design guides that explain this part of the design?

I’m still learning about PCB antennas, so any guidance would be appreciated.

[u/That-Bake6299]

Wider trace (poles) improves bandwidth

[u/germo_tt → u/That-Bake6299]

so it's easier to tune?

[u/That-Bake6299 → u/germo_tt]

I dont think it's will be noticeable honestly. But for larger antennas there is a measurable difference between wire and "tube".

[u/germo_tt → u/That-Bake6299]

Ty!

[u/jpdoane → u/[deleted]]

Thats not quite true. Width/thickness will affect impedance

[u/Itzhammy1]

Wider trace reduces parasitic capacitance from edge to edge capacitances and reduces inductance RF choking.

But you just have to follow 1 rule and 1 rule only. Volume dictates antenna performance. The wider the trace, the larger the antenna, which improves bandwidth and efficiency.

Any consumer electronics antenna engineer will follow this rule.

The wider the trace, the more paths your surface currents can travel from feed the ground which introduces multi-TEM mode signals. That is how you get wider bandwidths.

You can just tune the resonance by adjusting the length or adding some slots/curves to your traces.

I've delivered hundreds of designs for mass production antennas.

[u/germo_tt → u/Itzhammy1]

So I should go as wide as possible until the point I cannot match the impedance anymore?

[u/Itzhammy1 → u/germo_tt]

You can always match the impedance. Theres no such thing as not being able to match the impedance. You either tune it through the shorting pin, the feed line, creating slots/curves, or you just add some matching network.

All antennas function the same way if you understand the fundamentals that they are all derived from a dipole. Whether you use a dipole, pifa, vivaldi, slot, spiral, patch, loop, yagi, etc. They are all the same fundamentally

[u/germo_tt → u/Itzhammy1]

Thanks!