Antennas bring a unique set of considerations to PCB design
For antennas to maintain sufficiently high performance levels, their operating environment must be highly optimised. This article will explore some of the most important considerations when designing a printed circuit board.
Modern wireless devices are filled with far more technology than the devices of even a few years ago. This, coupled with a desire for smaller and smaller devices, means it’s more difficult than ever to guarantee a high level of performance. However there are simple ways to make sure your device will be optimised for wireless performance from the start of a project. For instance, utilising embedded antennas can help reduce PCB size while ensuring no dropoff in performance.
Ground plane space
Ground plane space is one of the key factors for an embedded antenna to perform well and, the smaller a device, the more important it is that space is sufficient. For instance, at frequencies under 1GHz, at least 90-100mm of ground plane is required for antennas to work in these devices efficiently.
Layout of components
The wrong layout of external components can easily unbalance a PCB and prove detrimental to its RF performance. Noisy, magnetic or moving components especially can detune and draw energy away from the antenna. To counter this, these components - as well as batteries and LCD screens - should be located an appropriate distance from the antenna.
The material of an enclosure can have a large bearing on wireless performance. Metallic product enclosures can inhibit it; this means if you absolutely must use a metal enclosure, it may be worthwhile looking at case-mounted antennas. In addition, some plastic enclosures also have the same effect in nullifying performance.
A sizable gap between the antenna and the enclosure is important to prevent the enclosure from absorbing RF energy. A gap of greater than 3mm is ideal to help keep the total power radiated high.
Vias are a useful tool to boost the suitability of multilayer PCBs for RF performance. For best results, you should cluster vias close together between ground fillings at the top layer and inner ground layer.