Minimum PCB size and reasonable antenna efficiency

[hcglitte]

Hi,

The datasheet for the antenna used in the dev kit, P822601, has its specification performance measured on a PCB DUT at 140 x 50 mm^2 - which seems rather unnecessary big, even for the lowest 700 MHz band. A smaller PCB (half size) should still produce adequate antenna performance, in my opinion, based on some similar antenna simulations.

I was wondering if nordic has done any testing with this antenna (or others) on smaller sized PCB's and measured the antenna efficiency.

Thanks 

[cbd]

I always thought that you looked for a ground plane that was related to the wavelength that you're trying to transmit, with full wavelength being the most efficient.

I guess that when supplying a datasheet a supplier will tend to give you the best case scenario.

[hcglitte]

I normally get good results when the ground plane is about 1/4 wavelength and the antenna is a meandering monopole. This is a good starting point for simulations (at least this is what I do). But I would love to see some real world examples where the PCB has been minimized to the minimum possible, still with OK performance. I wonder if nordic has done any such studies, would love to see some data.

[Martin]

I saw somewhere a presentation from Nordic with a new Thingy that has the same form factor (around 50x50mm) and incorporates a nrf9160 and an antenna from Fractus. 
I did a prototype with a TRIO mXTEND antenna that uses the same antenna for cellular and GPS (two feeds) and was having reasonable performance (but with an uBlox modem and GPS)

[Marjeris Romero]

Hi,

We encourage you to consult the antenna manufacturer regarding the minimum sizing of the ground plane and other performance data. A typical rule of thumb is to keep the ground plane larger than a 1/4 wavelength.

It is also possible to have a smaller ground plane but the antenna performance would gradually decrease as you decrease the ground plane. Different antenna parts will also have different performances at the same size of the ground plane, so that's why you should discuss this closely with the antenna manufacturer if you are not following the numbers given in the datasheet.

Changing the ground plane will also mean you need to change the matching components of the antenna specified in the datasheet (specially if the ground plane is smaller than a 1/4 wavelength).

Best Regards,

Marjeris