The importance of an IoT product’s antenna cannot be overstated. It is the interface to the outside world. In this article I will discuss why the antenna is important and how good or poor antenna performance can shape the customer’s perception of a product and thereby influence the product’s success.
I will begin by refreshing some basic theory. Next I will consider some of the strategies that a designer might use to improve communication, and illustrate that good antenna design is the most effective option. Finally I will illustrate how antenna design choices can have a significant impact on the success of a wireless or IoT product.
The antenna is one part of a system that conveys RF energy from a transmitter to a receiver. That system includes the transmitter, a method of feeding RF energy to the antenna, the antenna itself, the signal propagation path from transmit antenna to receive antenna, the receive antenna, a means of feeding RF to the receiver and the receiver itself.
For this system to work a sufficient level of signal must arrive at the receiver to allow the transmission to be successfully decoded. What constitutes a “sufficient” signal level depends on the noise level at the receiver so that level is expressed as a signal-to-noise ratio (SNR) in decibels (dB). (Noise is simply 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 can calculate the performance of the whole system using an equation like this (simplified example, using the standard abbreviations Tx and Rx for transmitter and 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 a link budget. We can calculate the signal received at the receiver and compare to the noise level, giving an SNR. If the SNR is high enough the signal will be successfully decoded.
Possible Strategies for Improving Wireless Communication
From this equation it is obvious that we would want to maximize the factors that have a positive impact on received signal (Tx power, Tx antenna gain and Rx antenna gain) and minimize the adverse factors (Tx feed loss, propagation loss and Rx feed loss). We would also wish to minimize noise at the receiver to improve SNR.
Transmitter power could be increased, but no transmitter is 100% efficient (wasted power is dissipated as heat) and doubling power equates to only a 3dB increase. Most projects lack the battery capacity and heat dissipation for high transmit power.
As RF engineers we can do little about noise in the environment but we can ensure the Rx antenna is located so as to maximize reception of wanted signals and minimize noise reception from other parts of the product.
Propagation loss depends on the distance between Tx and Rx antennas and what the signal must pass through. Signals propagate more readily through open air than metal, concrete or (in some cases) people. We must consider if anything in the product or how the product might be used could impair signal propagation.
The proportion of RF energy actually radiated by an antenna depends on whether or not it is correctly tuned for the frequency in use. If the antenna is not correctly tuned a proportion of the transmitted power is reflected back to the transmitter rather than being radiated by the antenna. The antenna must be designed for efficient performance at the required frequencies and designers should take care not to locate the antenna so that it becomes de-tuned by (for example) the product’s housing, it’s components or by the user’s body (such as the customer’s hand in the case of a handheld device).
The simplest (theoretical) antenna is the isotropic radiator. It emits a uniform signal in all directions, like an expanding sphere. That is known as the antenna “pattern”. No matter how the product, or antenna, is oriented the same signal will be received at the receiver. However no practical antenna is truly isotropic, they all radiate more signal in some directions than others. Sometimes this is desirable – for example if the product is fixed in one location – and yields more gain. But if the antenna on a wearable, handheld or mobile product exhibits a non-uniform pattern (meaning signal is emitted more in some directions than others) there is a risk that communication may be lost when the product is in certain orientations.
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Importance of Antenna Design in a Wireless or IoT Product
The importance of good antenna design, testing and integration should be apparent. A well engineered and tested antenna contributes to the success of a product by:
Providing gain (where appropriate, such as for fixed products) which increases radiated signal while consuming no additional battery power; and
Ensuring relatively consistent signal propagation in all directions (for wearable, handheld and IoT products) so that communication is not lost due to movement; and
Maximizing signal level while minimizing reception of noise through optimum 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); and
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 received SNR.
Improving the Rx power, and therefore SNR, will improve data rates, increase range, enhance safety & security and overall improve user experience. These factors not only promote customer satisfaction they enhance product performance in reviews and head-to-head testing as part of a product selection process.
We cannot rely on antenna designs from a reference implementation. Such designs 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 work on the test bench, but that is not adequate in a competitive market where wireless/IoT products depend on effective communication for customer satisfaction and, ultimately, success.
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 way the proximity of the customer’s hand or fingers caused 2.4GHz WiFi signals to be attenuated. This occurred because 2.4GHz signals are absorbed by water and the human body is more than 50% water. Although this issue was fixed in later models, the problem caused significant reputational damage and prompted customers to avoid the product. It was entirely preventable and should have been identified during simulation and/or testing.
In 2019 a different manufacturer of smartphones and tablets released a product that exhibited 2.4GHz WiFi performance problems when held in a particular orientation. This issue may have been caused by placement of the customer’s hands, or by a non-uniform antenna radiation pattern, or by a combination of both issues. The problem received widespread coverage in media and product reviews, causing reputational damage to the manufacturer.
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Disclaimer: The views and opinions expressed in this article are those of the author. It is intended only as a sharing of antenna design knowledge for educational purpose.