The second instalment of our webinar on the wireless design cycle explores the next two stages of the process - architecture layout and board design. Our Antenna Application Specialist, Geoff Schulteis, discusses the principal concerns for architecture layout as well as some tips for optimal PCB design including for:
- Wireless antenna integration for noise rejection
- RF trace impedance using CPWG design principles
- Laying out digital components
With any antenna, understanding where it’s placed will impact how it performs is essential. Particularly for an embedded antenna, the antenna needs to be positioned clearly away from the rest of the circuit – otherwise noise and other components can detune and impedance performance.
Most antennas perform best when positioned on the corner of the PCB. However, there are some antennas that operate best along the long-side edge. The datasheet of each antenna will detail the optimum placement of the antenna, as will the design of the evaluation board.
The gap between the casing/housing and the antenna is also an essential consideration. Plastic has a higher dielectric constant than air, so placing an antenna too close to it is likely to detune the signals.
Placing the antenna on the circuit board should be the first step in your board design. Antennas may be the only component that must be located in a specific physical position on the circuit board. This means you’ll need to consider:
- Ground plane size. Antennas use ground planes in order to radiate efficiently. In an antennas datasheet and EVB, there will be a recommended size of ground plane. This is not a minimum, but an antenna will perform less well under these circumstances.
- Component layout. Position noisy and metallic components away from antennas, where possible.
- RF coexistence. Plenty of wireless product designs harness multiple wireless technologies.
- Casing material. Metal housings are not conducive to RF performance. As well as the material of the casing, screens, batteries and metallic buttons can have RF implications. Position these away from antennas as best as possible. There are different solutions if the product requires a metal casing.
- Position RF circuitry within the vicinity of the antenna. Longer transmission lines are more prone to reflections and signal losses. This can reduce performance drastically – as much as 50% of RF energy can be lost through a transmission line.
Antennas have unique keep-out requirements. Some suggest certain keep-out zones which should be free of any components.