Cypress offers the following suggestions based on the antenna layout to optimize RF performance:
- Do not place components, mounting screws, or ground plane near the tip of the antenna, because the coupling of the antenna radiation to ground reduces the effective range of operation.
- In case of multilayer board, there must not be any GND plane near the tip of the antenna on any of the layers.
- The horizontal stub which runs to GND with the GND via is instrumental in increasing the return loss of the antenna.
- The antenna tip length may need to be compensated to optimize the antenna design for different board thickness.
- Avoid in-circuit test pins on RF nodes, because they create small antennas and may result in possible FCC issues and degrade RF performance.
- Large, continuous ground plane surfaces provide better radiation performance than small surfaces.
Some practical design guidelines for the antenna choice, selection, and implementation follow:
- It is disadvantageous to use any form of EMI/RFI shield coatings on plastic housing to solve EMI problems, without considering the effect of shielding on antenna placement and location.
- Eliminate connectors and interconnect transmission lines to avoid insertion loses on transmit power and receive sensitivity on the receiver.
- Product applications using keypads, LCD or other types of displays, battery packs, and other metallic surfaces affect and degrade the symmetry of the radiation pattern, reflections, and multipath. As a result, the location of the antenna placement is critical. Place the antenna for best balance of the distribution of these objects.
- If you are using an external antenna and connecting the antenna with a coaxial cable assembly, the cable routing needs to be designed in such a manner to keep it away from motors and battery packs.
- The orientation of the device and the product usage model during the operation must be considered in mounting the antenna inside the device.
- Note that the performance of the antenna is dependent on its immediate surroundings, packaging, and proximity to the ground plane. The placement of antenna position must be identified early in the design process.
- The effects of human body and the operator’s hand must be examined and validated away during the product operation. By keeping the antenna away, the Specific Absorption Rate (SAR) is reduced and pattern symmetry is improved.