Electronics Weekly Electronics Design & Components Tech News
The environment of smart devices presents design challenges. Electronic devices are increasingly being connected to the world through one or more wireless technologies and are commonly referred to as smart devices.
By 2025, it is estimated that more than 75 billion devices will be connected. The integration of multiple wireless technologies into smart IoT devices presents challenges for manufacturers, given environmental requirements such as the need to be waterproof and withstand high temperatures, shock and vibration. Rugged and robust designs, miniaturisation, long battery life and high performance are all critical factors that allow these devices to deliver reliable, seamless connectivity.
Antenna design considerations
Several factors can affect overall antenna performance, including ground plane dimensions, distance to nearby components, antenna position, PCB layout and component selection. Cutting-edge technologies, such as laser direct structuring (LDS) and metamaterial antenna technology, are also providing innovative solutions to free up space in smart devices.
The size of the ground plane is often dictated by the size of the device. For monopole or monopole-based antennas, ground plane size is critical for good antenna performance.
It should be at least λ/4 in size, where λ is the wavelength of the lowest frequency band of the monopole antenna. For lower cellular frequency bands (698-960 MHz), the λ/4 would be around 107mm. A ground plane of this size would not be suitable and possible for most smart IoT devices due to their small form factor. Therefore, a design consideration could be made to avoid monopole-based antennas, which are dependent on the ground plane for good performance.
Other antennas, such as dipole, could be used to overcome the ground plane size problem. Sometimes it is possible to extend the ground plane vertically if the height of the device allows. This technique makes it possible to have a large enough ground plane for monopole antennas for higher frequency bands, such as 2.4GHz or 5GHz.
Distance to components
Most antenna datasheets recommend a clear-out zone for the antenna to deliver optimum performance, as all components in smart devices can have an impact on antenna performance. Some components, such as the battery, display and charging coil, could detune the antenna. Surface-mount components close to the antenna on the PCB could detune and decrease the antenna’s efficiency. Sometimes, however, it is not possible to adhere to the guidelines provided by the antenna manufacturer. In such cases, a custom antenna design that mitigates the impact of nearby components may be necessary to achieve optimum antenna performance in the given environment.
Position is critical for antenna performance in small devices. Having a battery positioned a few millimetres away from the antenna would require a custom-designed antenna to mitigate the impact.
In small smart IoT devices, it is usually not possible to respect the clear-out zone requirements for the antenna. One solution could be to choose an antenna with a cable of a certain length to be mounted on the device housing away from the PCB. Another option would be to print the antenna on the inner or outer side of the housing, creating additional free space around the antenna and decreasing the impact from other components.
With printed antennas, it is very important to make sure that the housing material does not affect the antenna parameters and is not lossy on the desired frequency bands of operation.
For PCB layout it is critical to have a ‘clean’ RF ground plane without any signal routing on the antenna ground plane. High-speed data lines should be kept away from the RF lines.
The choice of components mounted on the PCB is very important in miniaturisation. By selecting smaller components and connectors it is possible to create more free space for the antenna and greater physical and electrical distance from other components. This helps in providing higher isolation and lower mutual coupling.
Laser direct structuring
LDS technology is used to create moulded interconnect devices and can save valuable space by integrating high frequency, mechanical and electrical functionality into one component. Laser structuring enables 3D design/routing capability, versus the limiting 2D capability on a PCB or other common substrates. LDS allows for improved antenna performance because antennas can be placed in the design where they have more room for better bandwidth and efficiency. The use of LDS technology is not limited to antennas, but can also be used for electromechanical, shielding and other components across an array of applications.
As we move into a world of devices that are handheld, wearable and wireless, the technologies that power these electronics must perform at higher proficiencies in smaller packages. This has created a rapidly expanding trend of miniaturisation. One of the main drivers for miniaturisation is the continually decreasing PCB size in IoT applications. Given reduced board real-estate, engineers require products with a compact form factor. The smaller the connectors are, the more that can fit into a reduced space, thus increasing the utility of the board.
PCB clearance is also a driving factor. Not only are PCBs smaller, but increasingly there are more per application and they need to be packed into a cavity that may have a unique or very thin shape. Connector protrusion of a board then becomes an important consideration, making low profile connectors a choice solution.
Connector selection
Connectors for miniaturised applications support key functions, such as data transfer, input/output (I/O), power and display. Proper connector selection with a holistic approach to device integration early in the design phase is paramount in meeting spatial, weight and performance requirements, as well as helping reduce late-stage changes that hinder speed to market.
Flexible printed circuit (FPC) connectors are suitable for miniaturised applications and connect to flexible PCB boards with chemically-etched traces that can conduct current. They come in low profiles (1mm height) and very fine pitches (0.25mm/0.3mm), although 0.5mm is the most common in the market and used primarily for LCD displays, which are increasingly being incorporated into smart devices. FPC connectors allow for flexible cable orientation, more creative routing options and custom PCB designs.
Fine pitch board-to-board and board-to-FPC connectors are optimised interconnects for small, thin electronic devices. They include a small centre line, narrow body and low mating height.
Free height connectors are two-piece, open pin field connectors designed for use in parallel stacking or mezzanine style board-to-board applications. They are offered in various combinations of plug and receptacle height, providing design flexibility with the ability to vary spacing between parallel boards; pitch from 0.5-1.25mm with stacking height from 1.5-20mm and from 20 to 440 positions.
Compressive board-to-board connectors enable connection to a gold-plated secondary board by compression of the contacts. This one-piece connector is designed for transmission of power and signal in miniaturised form factor applications. It is also scalable in a range of positions, height and pitch.
Catering for signals
High performance interconnects can be used where signal or low power needs to be routed through a device, that is, connecting ancillary items such as a fan, motor, sensor or switch. Centre lines range from 1-2.5mm and mounting options are vertical and horizontal (right angle). A locking option ensures secure mating retention, which is critical in applications that require high reliability or have high vibrations. Square-peg technology enables compatibility with industry standard products so they can be used at any point in the customer’s design cycle as a close alternative, or in some cases as a drop-in replacement.
A USB Type-C connector
Modular jacks are engineered to make secure and reliable I/O connections and include a variety of designations, configurations, sizes and beneficial features to address diverse design requirements. Shielded and unshielded registered jack connectors offer a one-piece construction with preloaded contacts, providing a quick-to-install, space-saving solution.
USB Type-C connectors are engineered to an industry standard that provides a sleek, slim and compact format for handheld devices and small home appliances, yet robust enough for industrial applications. These connectors feature a reversible mating interface and receptacle designed to accept a plug in any direction, which enables easy, reliable mating. They support a variety of protocols and, with the use of adapters, are backwards compatible to HDMI, VGA, DisplayPort and other types of connections from a single USB Type-C port. A distinctive EMI design on the back of the receptacle shell helps eliminate unwanted EMI leakage, while offering enhanced board retention features. Waterproof and splashproof options can deliver improved performance and reliability in rugged environments.
Spring fingers (also known as shield fingers, grounding springs or universal ground contacts) are single-contact, surface-mountable internal connectors with multiple functions on a PCB. As applications become more compact and miniaturised, spring finger contacts offer the best choice for grounding, antenna feeding and EMI shielding, given their small footprint and scalability. Most importantly, this allows for a scalable size spring finger that can use the same footprint, thereby minimising the need for a board redesign.
As the demand for smaller smart devices increases, so too will the need for even more miniaturised components that perform reliably and in harmony with other device components. Approaching the design phase with a holistic view of the impact of all components, including antennas and PCB connectors, is a critical step to avoiding unanticipated performance issues that can result in late-stage design changes, higher expense and delayed time to market. Consulting early and frequently with the antenna and PCB connector manufacturer is essential to identifying the right standard or custom-engineered components for an application’s requirements.
Metamaterial antenna technology
MetaSpan antennas use metamaterial antenna technology and are intrinsically designed with capacitive coupling and inductive loading, and offer benefits including:
* Enhanced low-band bandwidth and efficiency
* Reduced antenna size
* Intrinsic matching
* Improved stability compared to body loading
* Confined currents on or near the structure to prevent coupling with adjacent RF components or other antennas.
Combining the strengths of LDS and MetaSpan antenna technology deliver the ability to selectively and repeatably plate three-dimensionally. Other benefits are:
* Space savings
* Ability to produce thin (0.15mm) traces
* Improved antenna performance
* Applied cost savings
* Faster time to market
* Flexibility for pattern changes during production
* Simpler/faster/lower cost tooling.
