Antenna design - an example of integrated electronic and mechanical design thinking
Published on: 27th July 2017
Large metal components near the antenna such as batteries, motors or PCB ground planes will reduce wireless communications range both by attenuating the RF signal and by detuning the antenna circuit from the desired frequency. If the product is hand-held, poor antenna placement can lead to problems if the antenna can be masked by the user's hands or even touched if has been integrated into external product features. Even if production volumes are relatively low so an off-the-shelf RF module with an integrated antenna is used, poor location of this module within the product can severely reduce wireless communications range.
Where device cost is particularly sensitive, it is attractive to use a printed antenna on the PCB, as this has no additional parts cost. However, the board area required for the antenna itself and the necessary separation from other parts of the circuit can be significant and cause the PCB to grow, affecting the overall product size or form factor. A surface mount component can be used with a smaller footprint than a printed antenna, but this introduces additional parts cost and still limits the placement options to locations within the PCB footprint. By contrast, designing a bespoke antenna that is soldered to the PCB but extends beyond the board footprint can improve its location.
There may be an existing metallic part in the device that can serve a dual purpose as the RF antenna. This approach has to be evaluated on a case by case basis, as it can be difficult to achieve a good electrical connection without compromising the mechanical or visual design and even with careful testing and tuning to iterate and optimise the product layout, antenna design and matching circuitry, the RF performance may not be sufficient where a longer communication range is required.
The device casework can be another source of potential problems. Consumer devices are increasingly requiring metallised finishes to plastic casework to create a premium feel, which affects RF performance. Our experience is that the effects differ between treatments (for example, PVD compared to electroplating). If early prototypes are developed with bare plastic casework, repeating the antenna characterisation in a representative prototype when early metallised parts become available can reveal refinements to the antenna tuning that reduce the loss of range.
Antenna design is just one specific example of why a joined-up approach is required for the successful design and development of connected devices. Similar complex multi-disciplinary design decisions will need to be tackled throughout the product’s architecture. DCA’s tightly integrated system-based approach ensures that the product is designed as a whole, maximising our client’s probability of success.