Figure 4: Different antennas are available to suit various IoT applications. Image source: Amphenol
optimized for the target wireless interface’s RF band, for example, NB-IoT for multiple bands between 450 megahertz (MHz) and 2200 MHz, LoRa for 902 to 928 MHz in North America, Wi-Fi for 2.4 gigahertz (GHz) and 5 GHz, and Bluetooth LE for 2.4 GHz. Antennas employ different electrical concepts. Examples are monopole, dipole, loop, inverted F antenna (IFA), and planar inverted-F antenna (PIFA). Each suits a particular application. There are also single-ended and differential antennas. The single- ended type is unbalanced, while differential antennas are balanced. Single-ended antennas receive or transmit a signal referenced to ground, and the characteristic input impedance is typically 50
Ω. However, because many RF ICs have differential RF ports, a transformation network is often required if a single-ended antenna is employed. This balun network
Matching the antenna to the application The application and product form factor determine the final choice of antenna. For example, if an IoT product is space-constrained, a PC board antenna can be incorporated directly into the PC board circuitry. These antennas are an excellent choice for 2.4 GHz applications such as Bluetooth LE or Wi-Fi sensors in smart home devices, including lighting, thermostats, and security systems. They offer reliable RF performance in a low- profile architecture. Still, PC board antennas are tricky to design. An alternative is to source the pc board antenna from a commercial vendor. It can then be attached to the PC board using an adhesive backing.
transforms the signal from balanced to un balanced.
A differential antenna transmits using two complementary signals, each in its own conductor. Because the antenna is balanced, no balun is required when the antenna is used with RF ICs with differential RF ports. Finally, antennas come in several form factors, such as pc board, chip or patch, external whip, and wire. Figure 4 illustrates some sample applications.
An example of a PC board
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