Range is perhaps the most basic parameter that can help when determining the most appropriate protocol for a given application. This will cover short, medium and long range, spanning less than 10cm to many kilometres, respectively. Range is also closely related to data rate and this can often be a bigger determining factor than range, although of course the two are both largely dependent on power. Some protocols support only very low data rates but over long distances and at relatively low power levels, while higher data rates are typically restricted to shorter distances but may still require more system power to function.
Operating frequency is also defined by the protocol and most engineers will be at least somewhat familiar with the license-free bands allocated for Industrial, Scientific and Medical (ISM) applications and, within these, the 2.4-GHz band used by many of the most popular protocols. Despite using the same part of the spectrum, these protocols offer various ranges and data rates, which influences both their relative power requirements and the overall cost of radio devices. It is important to realise that the RF electronic circuitry defines the protocol, whereas the antenna simply receives and transmits RF signals fed to it by the electronics, irrespective of the protocol used.
This means that while the RF SoC/SiP used may differ between protocols, it is actually possible to use the same antenna design for any protocols that operate at the antenna’s intended frequency, such as those operating at 2.4 GHz (WiFi, Bluetooth, Zigbee, etc.). This means, of course, that one antenna can support several protocols. Having said that, there remain other relevant considerations when selecting an antenna, such as the physical space available and its location within the product. This will define the shape of the antenna, which may need to conform to a given profile in order to support the required frequency or bandwidth.