Where best place the antenna on PCB? Impact of ground proportions?

[d.s.]

Hi all!

Everywhere it can be read how important the dimensions of the groundplane are for a well working antenna... but what are the right dimensions? And where is the best place to locate the antenna on the PCB? Should de antenna be located at the longer edge or at the shorter edge of a non-square pcb? What should be minded to get a preferably omnidirectional radiation pattern?

Below eight different antenna locations are sketched - which one would be the best?

I have read many appnotes and whitepapers (including Nordic's "l/4 printed monopole antenna for 2.45GHz ") and I even designed some monopole and pifa trace antennas on pcb which worked well. However I wasn't able to find answers regarding my questions above so I never spent much attention to groundplane dimensions and antenna location so far.
I would be very glad if anyone could clear up my questions maybe ;)

Cheers

[Andreas]

Hi,

 

With regards to the size of the ground plane, larger is better, though as the ground plane gets larger the increase in antenna efficiency by further increasing it gets smaller and will converge against some value. The size will be relative to the wavelength, and a typical recommendation is that the size of the ground plane should be >= 1/4 wavelength, but as the size approaches a few wavelengths the impact of further increasing it starts to reduce. A larger ground plane will however make the antenna more broadband, thus more robust against detuning from enclosure and external factors.

Feed positions are hard to comment without analyzing it, ideally simulating the design. The ground plane is essentially half of a dipole antenna though, ideally this is infinitely large, but as long as it is > 1/4 wavelength and fairly evenly distributed there should not be too large differences. Factors such as position with regards to metal objects in the enclosure, human flesh when in use, traces and similar chopping up the ground plane, etc., will probably have a larger impact.

SMD antennas typically come with a recommendation from the manufacturer, suited for positioning in either a corner or along the center edge of the ground plane.

 

Best regards,

Andreas