Optimising your PCB for wireless performance

Sufficient ground plane space is integral for an embedded antenna to perform well. At sub-1GHz frequencies, there will be a greater impact on efficiency. As devices get smaller, ensuring there is sufficient ground plane space becomes more critical. Ideally, sub-1GHz frequencies require 90-100mm of ground plane to work effectively.

The layout and placement of external components can (and will) impact RF performance. Noisy, magnetic or moving components, in particular, can detune and draw energy away from the antenna. Consider placing these away from antennas to reduce noise. Batteries and LCD screens should also be placed in an appropriate location.

There are several things to consider with enclosures. Firstly, the material. Metallic product enclosures can inhibit wireless performance, so if these are necessary, it may be worthwhile looking at case-mounted antennas. Certain plastic enclosures can also detrimentally affect wireless performance.

You should also add a sizable gap between the antenna and the enclosure – greater than 3mm if feasible. If the gap is insufficient, the enclosure can absorb RF energy; reducing the total power radiated.

Vias are a useful tool for making multilayer PCBs more conducive for RF performance. Where possible we recommend to place plenty of vias close together between ground fillings at the top layer and the inner ground layer. The spacing between two vias should never be more than one-twentieth of the wavelength of the RF signals.