Small IoT devices face new challenges!

Designing antennas for compact IoT devices is a tricky task, but one that is becoming increasingly important. Learn more about this challenge and how to address it.

The Internet of Things (IoT) is a paradigm-shifting technology trend that is transforming everyday objects from refrigerators to watches into smart devices with internet connectivity. These objects can share data with each other, allowing for automation and enhancement of many aspects of daily life.

Antennas play a key role in these devices. An antenna is a device that converts electromagnetic radiation into electrical current and vice versa. This feature is critical in enabling IoT devices to wirelessly communicate and exchange data with each other, thus contributing to the interconnectivity that defines the IoT.

However, integrating antennas into these small IoT devices (Figure 1) is a significant challenge given the many limitations and considerations.

In the world of IoT, small is the new big: consumers crave compact, unobtrusive devices, and manufacturers strive to comply. These size limitations pose significant obstacles to antenna integration.

An antenna works by resonating at a specific frequency, and its size is usually proportional to the wavelength of the frequency at which it is designed to operate. For example, a dipole antenna operating in the 2.4 GHz band ideally needs to be approximately 6.25 cm long, a size that is generally not feasible for compact IoT devices.

Space within small IoT devices is very crowded, which creates a complex task for antenna integration. Antennas must function in close proximity to other components such as processors, batteries, and sensors. These components may interfere with the operation of the antenna, affecting its performance and ultimately the functionality of the device.

For example, the battery's metal casing, often the largest component in a compact IoT device, can interfere with the operation of the antenna in two ways: it can detune the antenna, changing its operating frequency, or due to its size, it can shield the antenna . antenna, reducing the effective radiation pattern and impairing device connectivity.

Similarly, processors, especially those running at high frequencies, generate large amounts of electromagnetic noise. When an antenna is brought closer, it picks up this noise, interfering with the reception and transmission of its signal.

The push for smaller, more compact IoT devices is great for portability and style, but has drawbacks when it comes to antenna performance. As these devices become smaller, the antennas inside them need to shrink as well. This reduction in size can negatively impact many important characteristics of how the antenna operates.

Some adverse effects of miniaturization on antenna performance include:

• Reduced Resonance Efficiency: Antennas work by resonating with a specific wavelength, and the size is usually proportional to that wavelength. As the size of an antenna decreases, its ability to effectively resonate with wavelengths is affected, resulting in reduced signal strength and reduced transmission range.

• Reduce bandwidth: Bandwidth refers to the range of frequencies that an antenna can effectively handle. Smaller antennas generally have more limited bandwidth due to their size. This means they can handle less data at any given time, which can slow down data transfer rates and hinder the overall functionality of the device.

• Increased susceptibility to detuning: In compact devices, the antenna is closer to other components. This close range can cause detuning, a change in the antenna's operating frequency caused by interference from other components, especially metal components.

• Impaired radiation pattern: An antenna’s radiation pattern, which describes the direction and strength of the signal it emits, can also be negatively affected by miniaturization. Smaller antennas often have less ideal radiation patterns, which can result in weaker and less reliable connections.

There are several potential solutions to these challenges:

An SoC integrates a microcontroller unit (MCU) and RF front end into a single silicon chip. By merging these two functions, SoCs can make good use of the limited space inside IoT devices. This space efficiency advantage is a key reason why IoT devices are increasingly being designed around wireless MCUs.

Despite these benefits, SoCs do not solve all problems: the physical size of the antenna is still limited by the wavelength of its operating frequency, and detuning (changes in the antenna's operating frequency caused by nearby components) remains a significant problem.

Another potential solution is to pair the SoC with a PCB trace antenna or chip antenna.

A PCB trace antenna is an antenna with conductors etched onto the PCB surface (Figure 2). They are cost-effective but take up considerable space, resulting in bulky IoT devices. Chip antennas, on the other hand, are smaller surface-mount components that save space. However, depending on whether they are connected to the ground plane, they may require a large amount of clearance area.

When using these antenna types, designers need to consider various factors to estimate the size of IoT devices. These include the required PCB dimensions for the antenna, the necessary clearance area, and the distance between the antenna and the edge of the device enclosure.

However, this approach comes with its own set of challenges. This often results in higher development costs as specialized RF design skills and equipment are required to design, test and tune. Additionally, there are certification fees to consider.

So, while pairing an SoC with these antennas can solve some space issues, it requires careful planning and may also increase time to market due to design, testing and certification requirements.

SiP is a module that integrates multiple components such as a microcontroller unit (MCU), radio frequency (RF) front end and antenna into a single package. SiP modules offer the compactness of an SoC while containing all necessary passive components, eliminating RF design challenges for engineers.

In addition to their compactness, SiP modules uniquely solve the notorious detuning problem in antenna integration. The antenna arrangement within these modules is designed for optimal performance even when placed close to the plastic housing. This design flexibility enables engineers to place SiP modules anywhere on the device, which helps reduce the overall size of the device.

The process of integrating antennas into small IoT devices presents significant challenges. These difficulties mainly arise from device size limitations and the negative impact of miniaturization on antenna performance.

Several solutions have been developed to address these challenges to some extent.

For example, combining an SoC with PCB traces or chip antennas can solve space constraints. However, this approach may extend the product's time to market due to the additional time required for the design, testing and certification process.

SiP provides a more comprehensive and user-friendly solution for antenna integration. These off-the-shelf devices feature integrated antennas, eliminating the need for complex RF design. In addition, they can effectively solve the antenna detuning problem commonly associated with compact IoT devices.