RF Cable and Antenna
Antenna design and RF cable are critical in a wireless system that transmits and receives electromagnetic radiation in free space. The wireless range that an end-customer gets out of an RF product with a current-limited power source such as a coin-cell battery depends greatly on the antenna design, the enclosure, and a good PCB layout. It is not uncommon to have a wide variation in RF ranges for designs that use the same silicon and the same power but a different layout and antenna-design practice. This application note describes the best practices, layout guidelines, and an antenna-tuning procedure to get the widest range with a given amount of power. Other important general layout considerations for RF trace, power supply decoupling, via holes, PCB stackup, and antenna and grounding are also explored. The selection of RF passives such as inductors and capacitors is covered in detail. Each topic ends with tips or a checklist of design items related to the topic. A well-designed antenna ensures optimum operating distance of the wireless product. The more power it can transmit from the radio, the larger the distance it can cover for a given packet error rate (PER) and receiver sensitivity. Similarly, a well-tuned radio at the receiver side can work with minimal radiation incident at the antenna. The RF layout together with the radio matching network needs to be properly designed to ensure that most of the power from the radio reaches the antenna and vice versa.