How to avoid antenna-related IIoT wireless module failures

Introduction

The wireless age of industrial automation, factory machines and transportation, otherwise known as the industrial internet of things (IIoT), is now blossoming. There are many wireless standards and technologies to choose from, including cellular standards 2G, 3G, 4G and now 5G. Bluetooth and Zigbee have long been seen in industrial applications, as well as Global Positioning System/Global Navigation Satellite System (GPS/GNSS) and industrial, scientific and medical (ISM) band technologies. Wi-Fi is now emerging with new industrial features, a frequency band at 6 GHz and other use cases, though Wi-Fi has been used in the space for some time, as has low-power wide-area network (LPWAN) technology. These standards are steadily evolving to enable more industrial use cases, improve reliability, enhance efficiency and simplify the processes of deploying state-of-the-art wireless solutions.

However, one component of the industrial wireless module can make or break the solution: the antenna. Without proper design, assembly and installation, even the most advanced antenna designs are not able to compensate for poor antenna performance. It is unfortunately common for new and established industrial wireless solutions providers to make blunders in the selection, placement or installation of wireless antennas that result in unreliable connectivity, weak signal strength, interference and wireless solutions not performing to expectations.

This article aims to highlight the pitfalls of industrial wireless antenna selection, placement and installation, and offers guidance about avoiding these pitfalls, thereby leading to successful industrial wireless solution deployment.

Antennas in industrial wireless solutions

Antennas for wireless telecommunications translate electrical signals sent along conductors to electromagnetic waves traveling through the air, and vice versa. The symmetric behavior of wireless antennas is extremely useful, as an antenna that successfully transmits signals at a given frequency and configuration will also successfully receive them. Antennas feature conductors and dielectrics designed in a geometric fashion to exhibit a specified frequency response. Factors that determine an antenna’s performance include size, design and materials. However, other factors also directly impact antenna performance, especially in cluttered and noisy industrial environments.

Antenna selection for IIoT applications

There are several antenna typologies with various degrees of performance for given functions. Fortunately, sorting through the complexity of antenna options and selecting an antenna can be more straightforward when considering critical electrical and mechanical performance parameters. Note that the assembly and installation of an antenna directly impacts the resulting performance and may only marginally impact the performance or render the antenna inoperable if improperly assembled and installed.

Electrical parameters

The three main antenna parameters to consider are efficiency, bandwidth and gain (directivity). The efficiency of an antenna is a ratio of the radiated power of the antenna at a given frequency compared to the electrical power supplied to the antenna. The innate conductor losses and various aspects of the antenna design ultimately result in a real-world efficiency of less than 100%. A quality antenna designed for high antenna efficiency radiates beyond 50% of the power supplied to the antenna. Antenna efficiency is critical for IIoT applications where a wireless node is powered by renewable energy or a battery, and energy requirements are strictly budgeted. Long range wireless communications also benefit from high efficiency antennas, as higher efficiency antennas require less power to be fed to high power antenna structures and results in lower power and lower cost RF front-end (RFFE) hardware and electrical power operating costs.

Figure 1. Multiband antenna efficiency for various bands. Source: TE Connectivity

The bandwidth of an antenna is the frequency range for which the antenna behaves as specified. Generally, this means the range in which the antenna gain is at a desirable level. Some antenna designs and topologies result in a frequency response that performs better at certain frequencies than others. An antenna’s bandwidth may be a small frequency range for narrowband applications, a very large swath of spectrum for broadband applications, or even several distinct frequency bands for multiband antenna.

The gain and directivity of an antenna are related parameters. The gain of an antenna is how well the antenna radiates compared to an isotropic antenna that radiates equally in all directions. As such, the gain of an antenna is measured according to the direction in 3D space to an antenna radiating perfectly evenly in a spherical pattern. No real antenna does this, but it is used as a standard for comparison, nonetheless.

The directivity of an antenna is a measure of the power density of the antenna in the direction of maximum radiation in 3D space divided by the average of the antenna’s power density. In some cases, an antenna is needed to radiate in a specific direction efficiently. This would generally require a highly directional antenna, which can reach peak gains around 20 dB. However, some use cases require radiation patterns that cover a wide area surrounding the antenna, and an omnidirectional antenna is needed. It is important to note that highly directive antennas have much lower gain in directions outside of the main lobe and may operate poorly if not properly aligned. Omnidirectional antennas may also have a radiation pattern favoring the horizontal direction, which would mean decreased signal strengths in the vertical directions (donut shaped radiation pattern). There are also areas of very weak signal strength of the antenna pattern, known as nulls, and are a reason why matching the antenna pattern to the placement of wireless nodes and gateways is essential.

Physical parameters

Outside of the electrical parameters, there are several important physical parameters for IIoT antennas to consider. Mainly, these factors have to do with the size, weight and interconnect style of the antenna. There are many different types of IIoT antennas; some are very specifically designed for a given application, and others are more generically designed to be useful for a wide range of applications.

As the size of an antenna directly relates to its electrical parameters, it is important to determine the wireless device performance requirements when deciding on an antenna footprint. Antenna sizes range from miniscule surface mount technology (SMT) chip antennas, onboard printed circuit board (PCB) antennas, antenna “daughter” boards that snap onto a PCB, to discrete antenna modules connected through transmission lines (usually coaxial cable assemblies) to the wireless device PCB or exposed ports. IIoT antennas may have board mount interconnect, soldered planar transmission lines (microstrip) or use discrete coaxial cable assemblies that can be chosen to allow some degree of freedom of the antenna placement in respect to the wireless device.

Antennas must often be mounted in exposed locations that are strategically chosen to offer maximum coverage or range. This often results in an antenna being mounted high up or on overhangs, which make the weight of an antenna critical. The antenna adds to the overall weight of the wireless node or gateway, which may even be small in comparison to the antenna. Therefore, the size and weight of an antenna are essential in determining the type of mounting hardware needed or for designing the wireless device assembly/enclosure.

Assembly and installation

Dielectric and conductive materials placed in close proximity to an antenna will intrinsically interact with, and change, the performance of an antenna. Therefore, it is important to consider antenna placement at every stage of the wireless device assembly and installation to ensure that antenna placement is adequate to meet desired performance requirements. As there are always tradeoffs in design, integrating an antenna will likely not yield results that directly match data sheet performance, and thorough testing is helpful in sorting out these challenges.

Antenna placement

If an IIoT wireless device includes an antenna integrated into the assembly/housing/enclosure, then it is likely that the antenna of the device will be in close proximity to conductors, dielectrics and other electrical circuits. Antennas, mainly conductors and dielectrics, will couple magnetically, electrically and electromagnetically with nearby conductors, which inevitably results in a change of the antenna performance. Moreover, nearby electrical circuits may present loading effects through the coupling that allows for interference to be more efficiently conducted into the external circuits or to the antenna.

Also, placing antennas close to structures that experience or generate shock or vibration can result in undesirable antenna behavior as internal antenna structures or antenna transmission lines may vibrate or shift out of alignment due to excessive mechanical stresses. Similarly, exposing an antenna to thermal cycles or thermal variations beyond manufacturing specifications could also result in degraded antenna performance from thermal expansion or contraction, inducing tolerance changes, derating dielectrics or reducing antenna conductivity.

As any grounded conductor can block the electromagnetic signal path to and from an antenna, understanding that an IIoT needs to be assembled outside of a grounded metal enclosure is needed, which may result in trade-offs of assembly or enclosure design complexity. This is why there are bulkhead coaxial connectors to bridge between a metallic enclosure and a discrete antenna while still providing shielding to the circuits within the enclosure and low loss interconnect to the antenna.

Figure 2. Datasheet guidance on antenna assembly and placement. Source: TE Connectivity

Installation of IIoT wireless solution within a facility

Industrial facilities are typically rife with high power electrical circuits, electromagnetic interference (EMI) from drivers, interface memory and GPU processors and electrical actors, and a diverse range of industrial processes related interference. Considering noise level can help in selecting the appropriate antenna solution, as well as the placement of wireless nodes and gateways. In less noisy environments, the receivers of the wireless devices will be more sensitive and may demonstrate longer range operation.

However, in noisier environments, wireless system range may be reduced due to desensitization of a receiver. In this case, choosing another antenna location or antenna structure together with proper board level shielding would help to guarantee sufficient RF performance. Directive antennas are typically better suited to use in external point-to-point applications, or for use in so-called terminal mount or cabled antennas outside of a device enclosure (which may include EMI shielding).

Conclusion

All of these factors are essential to consider when selecting, assembling and installing IIoT antenna solutions. This is often challenging and there is no one-size-fits-all antenna solution or installation guidance. Experts in IIoT antenna solutions and installation are invaluable partners in achieving a successful IIoT wireless service deployment that is both reliable and meets industrial requirements. Visit the RS Components’ website for more information.

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