As the Internet of Things (IoT) starts to materialize, more and more consumer and industrial products are incorporating wireless interfaces such as Bluetooth, WiFi, GPS, or proprietary wireless radio technologies. Adoption of such features has been accelerated by the availability of low cost, integrated modules from a variety of vendors.
Modules and reference designs alike will typically specify one or more particular antennas and its match as determined by the vendor. However, this ideal match is nominally determined in an ideal or “typical” environment, most often without any materials nearby which might detune the antenna, reducing its effectiveness and ultimately the range and/or reliability of the wireless interface. When the module includes an antenna on-board, only the module location and surrounding materials can be adjusted to optimize the antenna match. But when a module with external antenna or reference design is adopted, it is possible to optimize the antenna’s performance in the product’s actual housing, and including the effects of the PCB itself.
This application note, explains the S11 measurement at an introductory level, talks about some of the specific tools and techniques which will be useful when measuring and optimizing wireless antennas and their matching networks.