Wireless and Antenna Selection Priorities in IoT Applications
Illustration: © IoT For All

The Internet of Things (IoT) has influenced almost everyone’s life and work in recent times. For some, their engagement with IoT is as simple as using a smartwatch to track their eating or exercise habits. They may also take advantage of the utility company’s smart meter to save energy and keep bills under control. These engagements underscore the significance of wireless and antenna selection in IoT applications.

At the other extreme, it has become possible to connect everything, including appliances, lighting, heating, door locks and security, and solar panels, controlled and managed through a home digital assistant.

Outside of domestic environments, industrial and business use cases are typically more diverse. These aim at automating building systems to improve efficiency and reduce carbon footprint. They also involve collecting vast amounts of data to enhance process control, business planning, asset management, equipment maintenance, and more. This data aids in improving energy and waste management and even new-product conceptualization and design.

Latest Wireless Protocols

Wireless technologies offer several inherent strengths for connecting IoT devices. Flexibility stands out as a key advantage, enabling the deployment of devices in various locations, unconstrained by physical cabling. Installing new wires in the home, office, or factory can be disruptive. Wireless and antenna selection is often cost-effective, especially for large-scale IoT deployments, and allows easy, inexpensive scalability.

Mobility is another advantage, offering a powerful enabling factor in applications like wearables and asset tracking. Additionally, the power efficiency of wireless technologies can be important in battery-operated IoT devices.

Wireless Selections

Standardized wireless technologies commonly used in IoT applications include NFC, which is ideal for data exchanges of short duration over distances of a couple of centimeters. The energy contained in the RF field emitted by an NFC reader device can be enough to power the receiver circuitry to retrieve and transmit memorized data as requested.

Bluetooth connectivity offers mobility and allows flexibility to engineer the data rate, range, and power consumption to meet the requirements of a given application. It allows point-to-point and mesh connections and the latest versions also support direction finding and location sensing. Conceived from the outset for mesh networking, Zigbee has similar characteristics.

Users may prefer Wi-Fi in cases where a longer range, higher data rates, or larger connection capacities are needed. Several Wi-Fi generations remain in service, up to Wi-Fi 6, which has a theoretical maximum data rate of 9.6Gbps. Wi-Fi 6 also features flexible channel allocation and techniques to reduce interference and waiting times to connect to the network. Additionally, its beam forming can improve data-transmission efficiency and enhance WPA3 security.

In IoT applications that need longer range and greater mobility, choices include cellular and low-power wide-area network (LPWAN) technologies such as LoRa and Sigfox. As legacy networks switch off, older 2.5G and 3G data connections give way to standards like LTE-M and NB-IoT that use the latest LTE and 5G networks. These are optimized to meet the needs of IoT applications, which typically call for frequent exchanges comprising small quantities of data.

Devices such as asset trackers can rely on navigation-satellite constellations (generically termed global navigation satellite systems, or GNSS). Examples include GPS, Galileo, GLONASS, and BeiDou. Multi-constellation receivers can benefit from a more rugged and robust availability of location data.

Some receivers can offer access to special high-accuracy services provided by satellite operators. A tracker can calculate location using the embedded GNSS subsystem and share this information with the host IoT application over a wireless connection such as LPWAN or cellular.

Wireless and Antenna Selection

Essentially, an antenna transfers signals between the electromagnetic and electrical domains, leveraging resonance at the RF carrier frequency. This requires the antenna’s effective length to be a specific fraction of the carrier signal’s wavelength.

Hence, size is important when considering wireless and antenna selection. The size is directly related to the frequency band at which the antenna operates. This depends on the chosen wireless technology and associated operating frequency.

In addition, antenna packaging is a critical issue that affects component selection. IoT devices can be subject to stringent size limitations. This calls for antennas to be small while offering high performance. Sealing is often required, particularly in items like remote sensors and smart meters, which can be exposed to harsh conditions and are expected to remain in service for extended periods.

A portfolio that offers a choice of PCB-mount, internally mounted, and external antennas, optimized for specific frequency bands and wireless technologies often used in IoT applications, can help designers choose the best type for their application. Such portfolios offer different types and sizes, choices such as soldered or coaxial connections, and parts optimized for specific technologies such as NFC and GNSS antennas.

NFC Antennas

Several factors influence the selection of wireless and antenna for NFC applications. NFC operates at 13.56MHz, so the antenna must be designed to resonate at this specific frequency to ensure optimal communication. Wire-wound antennas and loop antennas are commonly available as off-the-shelf components.

While the effective antenna length is related to the operating frequency, NFC antennas also have a role in harvesting energy from the RF field emitted by reading devices to power up the IoT device’s embedded microcontroller, memory, and additional hardware that may include a security IC, to gather and transmit the data requested by the reader.

Final selection can depend on variables like the form factor of the device and the desired read range. Typically, smaller antennas are compact but offer shorter read ranges, while larger antennas provide longer read ranges. The available space within the device or application will dictate the antenna size.

Generally, some NFC antennas can be more sensitive to orientation than others, which can require extra care when selecting a specific model and determining its optimal position in the device. It may be integrated into the circuit board or affixed to the enclosure.

Metal objects, electrical interference, and other environmental factors can affect antenna performance. Shielding or appropriate placement may be necessary. Proper impedance matching between the NFC chip/module and the antenna is essential to maximize power transfer and minimize signal loss.

Antennas for Commonly Used Technologies

For wireless technologies such as Bluetooth and Wi-Fi operating at 2.4GHz, as well as cellular and LPWAN technologies, there is a broad selection of PCB-mount, internal, and external antennas. The choice depends on factors like the device’s form factor, size constraints, and the desired range of communication.

Chip-size antennas are available for Bluetooth and Wi-Fi 2/3/4 applications in the 2.4GHz frequency bands for industrial, scientific, and medical applications (known as ISM bands).

External antennas tend to be of either monopole or dipole design. A monopole type consists of a single wire that requires a ground plane to reflect the radio waves and help shape the radiation pattern. The pattern is omnidirectional.

The dipole type has two conductive elements separated by a gap. These are often half-wavelength antennas, usually longer than a monopole, although the gain is typically greater, and the radiation pattern is bidirectional. The antenna’s gain directly affects the device’s range and coverage. Antennas with higher gain can provide a longer communication range.

Many opt for cellular connectivity for small devices like trackers mounted on movable assets such as cars, vans, or construction vehicles. In these applications, an internal antenna may be appropriate to permit less obtrusive installation or to keep fragile parts out of harm’s way. On the other hand, a larger external antenna may be suited to a device such as a gateway designed to direct data from multiple IoT endpoints into the cloud via a cellular connection.

GNSS Antennas

GNSS antennas come in various styles, such as ceramic patch antennas. As a type, they have circular polarisation that ensures high sensitivity to the satellite signals. When designing equipment such as asset-tracking devices with satellite locations, designers must ensure that the chosen antenna supports the relevant constellations.

Conclusion

Size and packaging are critical issues to consider when choosing an antenna for an IoT application. Large external antennas tend to offer the most favorable RF performance. On the other hand, internal mounting is often preferred to withstand environmental challenges and allow easier use and portability, while surface-mount antennas can offer a solution when size constraints are extreme. Choice is the designer’s friend in the search for the best combination of electrical and physical properties.

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