Enabling the I in IoT: Antennas in IoT Product Development

The importance of antennas in IoT product development cannot be overstated. The antenna is the device’s interface to the outside world; it is the component that enables the “I” in IoT. Since the capabilities of an antenna is directly tied to most – if not all – of the integral features, it’s also one of the most important components that shape the customer’s perception of a product.

This text will freshen you up on some of the basic theory on the subject. Following that, we’ll delve into different strategies that could improve the communication capabilities of a device. As a conclusion, we’ll use some real-world examples to illustrate how the performance of an antenna significantly influences the success of wireless and IoT products.

Let’s start with the basic structure. The antenna is a part of a system that conveys RF energy from a transmitter to a receiver. The system as a whole is quite complex, and includes many parts: the transmitter, the method of feeding RF energy to the antenna, the antenna, the signal propagation path from the transmit antenna to the receive antenna, the receive antenna, the means of feeding RF to the receiver, and finally the receiver.

For this complex system to work, a sufficient level of signal must arrive at the receiver. Otherwise, the transmission cannot be successfully decoded. What constitutes a “sufficient signal level” depends on the noise level at the receiver. That level is expressed as a signal-to-noise ratio (SNR) in decibels (dB). “Noise” in this context means any unwanted signal, such as interference generated by other electronics. Gains and losses are expressed in decibels; transmitted and received power levels are normally referenced to a level of 1 milliwatt and expressed as dBm.

We calculate the performance of the whole system using an equation. This is a simplified, illustrative example. Tx and Rx are abbreviations for the transmitter and the receiver.

Rx power (dBm) = Tx power (dBm) – Tx feed loss (dB) + Tx antenna gain (dB) – propagation loss (dB) + Rx antenna gain (dB) – Rx feed loss (dB)

This equation is known as the link budget. We calculate the signal received at the receiver and compare it to the noise level, giving an SNR. If the SNR is high enough, the signal will be successfully decoded.

Now that we have a basic understanding, we can theorize different strategies on how to improve the connection. From the previous equation we can surmise, that we want to…

• maximize the positive factors (Tx power, Tx antenna gain and Rx antenna gain) of the received signal
• minimize the adverse factors (Tx feed loss, propagation loss and Rx feed loss) of the received signal
• minimize noise at the receiver to improve SNR

One initial idea could be to increase transmitter power, but unfortunately no transmitter is 100% efficient. Power is wasted as dissipated heat, and even doubling power equals to only about a 3dB increase. Most devices also lack the battery capacity and heat dissipation for high transmit power.

RF engineers can not really affect the NOISE in the environment, since the SNR is DICTATED by all of the electronical components of the device. What we can do, however, is to circumvent the problem! Even if the amount of noise stays the same, changing the location of the Rx antenna can maximize the reception of wanted signals, whilst minimizing noise reception from other parts of the products.

Propagation loss depends on the distance between Tx and Rx antennas, and what the signal must pass through. Signals propagate more easily through open air than metal, concrete or people. This is a vital part of product design: signal propagation is affected by the way the product is used, as well as everything in and around the product. This is especially important to understand when developing wearable and mobile devices.

The proportion of RF energy actually radiated depends on whether or not the antenna is correctly tuned for the used frequency. Without proper tuning, a portion of the transmitted power is reflected back to the transmitter, rather than being radiated by the antenna. The antenna must also be designed for efficient performance at the required frequencies; designers should not choose a location where the antenna becomes de-tuned by any factor, such as the product’s housing or components, or the body of the user.

If we move on to the antenna selection, the simplest (theoretical) antenna is the isotropic radiator. It emits a uniform signal in all directions, like an expanding sphere. This is also known as the “antenna pattern”. No matter how the antenna or the product itself is oriented, the same signal will be received at the receiver. However, no practical antenna is truly isotropic: every antenna radiates more signal in one direction compared to others. This might even be desired, particularly when the device is stationary. Remaining in a fixed position also helps the antenna yield more gain. On the other hand, if the antenna of a wearable or mobile device produces a non-uniform pattern (meaning that the signal is emitted unevenly between directions), there is a risk that the communication may suffer because of it.

To summarize, a well-engineered antenna provides:

• Increased radiated signal without consuming additional battery power
• Consistent signal propagation in all directions for wearable, handheld and IoT devices
• Maximized signal level while minimizing reception of noise through optimal location (particularly to minimize noise reception from other components in the product, avoid signal shielding from the product or housing and to ensure the antenna is not de-tuned)

Note that there are two antennas involved in each communication – the Tx antenna and the Rx antenna! Therefore any improvement in a product’s antenna performance drives a two-fold improvement in the received SNR.

It’s also important to understand the corresponding effect: by improving the Rx power, we naturally improve the SNR as well. Improved SNR will then improve the data rates, range, safety and security; everything factoring into a better overall user experience. These factors enhance product performance, and in the end, customer satisfaction.

Every device is different. This is another fundamental principle that must be taken into account. Some product developers may try to CUT CORNERS by implementing and older antenna design for a cost-effective APPROACH, but unfortunately this is rarely a truly cost-efficient. Reference implementations do not take into account product-specific factors such as housing and component layout. Reference designs are intended to provide guidance, rather than be an optimized, customer-ready solution. They may even work on the test bench, but that is not an adequate solution in a competitive market where wireless/IoT products depend on effective communication for customer satisfaction.

In 2010, the manufacturer of a well-known smartphone released a new product with a (now notorious) antenna design flaw. If the phone was held in a certain angle, the proximity of the customer’s hand or fingers caused the 2.4GHz Wi-Fi signals to be attenuated. The reason behind this occurrence? The composition of the human body. 2.4GHz signals are absorbed by water, and more than 50% of the human body consists of water. Although this issue was fixed in later models, the problem had already caused significant reputational damage and prompted customers to avoid the product. The issue was completely preventable, and should have been identified during the testing phase.

In 2019 a different manufacturer of smart phones and tablets released a product that exhibited problems in the 2.4GHz Wi-Fi performance, when held in a particular angle. This issue may have been caused by the placement of the customer’s hand or by a non-uniform antenna radiation pattern – or both. Whatever the underlying problem ended up being, the performance issues received widespread coverage in media and product reviews, causing huge reputational damage to the manufacturer.

These examples are not one of a kind. Modern devices that use groundbreaking technology have a million moving parts, and as such there are a million and one problems that can happen – that’s something we can’t really do anything about. What we can do, however, is minimize unnecessary risks. With professional antenna engineers, we can design a reliable device with improved and consistent performance.

Read more about Radientum’s IoT-related services or contact one of our account managers about design work for your product.