Questions about trace antenna

[Juniorprogrammer]

Hi,

I have some questions about the quaterwave monopole antenna. 

In the papers of Nordic I did read:

If the ground plane size is considerably smaller than the ideal size and/or much of the antenna trace is routed close to the edge of the PCB, then the length of the antenna trace should be extended by about 30%. For an example, see Figure 1b.

What is meant with ideal size?

And how much gain do I expect with this type of antenna?

Br,

JP

[Kazi Afroza Sultana]

Hello JP,

The ground plane of the PCB should be longer than the 1/4 of the wavelength; For example: if the band is 700 MHz, it should be 10 cm or so. When a PCB size is small like 50mmx50mm, it is difficult to get the proper ground plane. Then you need to do some adjustment to get the accurate signal strength. It could be changing the size of antenna, adding extra switches (you can look at our Thingy:91 design (https://nsscprodmedia.blob.core.windows.net/prod/software-and-other-downloads/dev-kits/thingy91/hardware-files/thingy91---hardware-files-1_6_0.zip)) to tune the antenna in different frequency bands etc. 

Small size 2_4GHz PCB antenna (2).pdf

I am attaching an application note of a 2.4 GHz PCB antenna for your understanding.

''And how much gain do I expect with this type of antenna?''

It depends on the size of the ground plane. So based on the applications the design would be different. So, there is no specific number for this. 

I hope it helps. Feel free to ask more questions if you have. 

Thanks.

Best Regards,

Kazi Afroza Sultana

[Juniorprogrammer]

Hi Kazi,

Firstly thank you for your reply.

Kazi Afroza Sultana said:

it should be 10 cm or so. When a PCB size is small like 50mmx50mm,

Is this the total ground plane of the PCB or the ground plane under the antenna. 

Kazi Afroza Sultana said:

It depends on the size of the ground plane. So based on the applications the design would be different. So, there is no specific number for this. 

Is there a way to calculate it, so how?

Kind regards,

JP

[Kazi Afroza Sultana]

Hello JP

''Is this the total ground plane of the PCB or the ground plane under the antenna.'' 

Total ground plane.

''Is there a way to calculate it, so how?'' This is mostly simulated with computer tools. There is no direct method to calculate it. Ground plane, antenna shape determines the gain. It depends on your design. What is your exact plan? You may contact to antenna design companies like Fractus, Ignion or Johanson technologies.  

Thanks.

BR

Kazi

[Juniorprogrammer]

Hi Kazi,

"Total ground plane."

In the papers of the monopole antenna I did read this:

So in figure B the total ground plane is lager than the antenna. But it says it have to be 30% extended.

Or do I get it wrong?

Br,

JP

[Juniorprogrammer]

Update: 

Sorry Kazi, but I think I did get it. In figure b the trace is routed to the edges. I think that is the reason to expand the length with 30%.