Latest developments in antennas for M2M communications
Machine-to-machine (M2M) communications has undergone phenomenal growth in recent years. Product performance and usage information is collected via uplinks. Downlinks deliver control and software updates. Growth in the much-heralded “Internet of Things” (IoT) will accelerate the trend. Analyst Gartner predicts that there will be some 26 billion connected devices in the world by 2020. Wearable electronics will account for the biggest chunk of this but there will be many other consumer and industrial applications. Connectivity will become increasingly reliant upon wireless, rather than wired networks. Local networks are usually implemented using industry-standard protocols, with wide-area connectivity handled over public cellular networks or dedicated private links.
This growth in wireless networks will mean that an understanding of antennas and radio propagation is becoming essential for electronic system designers who may previously have had little or no experience of these technologies. And selecting the most effective antenna for a given application will not just be about finding the smallest, or the cheapest. Antenna selection, like most design decisions, will be about trade-offs in form-factor, size, performance, and cost. Where cellular networks are employed, the choice of antenna becomes more complex with each new generation, as do the system certification testing and compliance requirements.
For many systems, the choice of antenna will be the single most important decision for the electronics designer. Doubling the power output of a transceiver only increases signal strength at the receiver by 3dB, but doubles the rate at which energy is drawn from a battery. If an antenna that provides gain in one or more directions can be used, both the effective transmitter power and receiver sensitivity can be greatly enhanced, with no penalty in battery consumption. Alternatively, the right antenna may enable a system to operate effectively, with adequate signal-to-noise ratio (SNR) and range, at much lower input power levels, extending the system’s operating life between battery charges, or battery swap-outs.
You don’t need a multi-element array like a UHF TV aerial to achieve gain from an antenna. A single-element antenna that is omnidirectional in the horizontal plane delivers gain over an isotropic source - one that radiates equally in all directions, including up and down. Unless a radio is going to be completely static, single element antennas are usually the preferred option. If you want to find out more about basic theory, here’s a great primer on antennas from Ian Poole.
One of the key decisions in designing a radio link is whether to go for single channel or Multiple Input Multiple Output – MIMO for short. MIMO uses several antennas so that reflected signals can be captured. It’s much more complex than a single channel link but yields advantages in terms of data throughput and robustness in the presence of both physical obstructions and EMI. MIMO delivers several signals to the receiver using diversity of one kind or another. If a signal becomes deficient, the idea is that the link is maintained by one of the others. These signals can be separated by time, frequency or physical space.
One of the most comprehensive sources of information on MIMO is “MIMO Wireless Networks”, a book by Bruno Clerckx, an assistant professor at Imperial College London, and Claude Oestges, a professor at ICTEAM UCLouvain in Belgium. It’s available as an e-Book or in print.
These are the most popular frequency bands and applications used in M2M communications:
- GSM, CDMA and WCDMA (850/900/1800/1900 MHz)
- UMTS (2100 MHz)
- GPSBT/802.11
- Dual-band GSM900/1800 MHz
- Dual-band GSM850/1900 MHz
- Tri-band GSM900/1800/1900 MHz
- Tri-band GSM850/1800/1900 MHz
- Quad-band GSM850/900/1800/1900 MHz
- Penta-band GSM850/900/1800/1900/2100 MHz
- Tri-band GSM + GPS
- Tri-band GSM + BT
- LAN
- WiMax: 2300 to 2700 & 3300 to 3800 MHz
- ISM 900/ZigBee®: 902 to 928 MHz
- Bluetooth®/ZigBee®: 2400 to 2483.5 MHz
- UWB: 3168 to 10560 MHz
- GPS: 1565 to 1585 MHz
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In many IoT designs, fitting the antenna into the device will be one of the prime considerations. Antennas can be tracks printed onto a PCB, surface mount chip components, externally mounted ‘fingers’ or a host of things in between. Whichever type you choose, the smaller the antenna for a given frequency range the less effective it is. You do find small, high-efficiency antennas, but they tend to have very narrow bandwidth, which may not be sufficient for some types of radio link.
The Molex range is one of the most comprehensive. The neat dual-band dipole (2.4 and 5GHz) antenna (left) doesn’t need a ground plane and is easily mounted by simply peeling off its backing tape and sticking it to a convenient surface. Part of the 47950 series, it’s 70% efficient at 5GHz and 80% efficient at 2.4GHz.
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Our TE Connectivity antenna selector guide (right) provides information on over 21 types of antenna covering most of the applications and frequency bands mentioned earlier. It kicks off with a basic guide to antenna specifications, so is particularly useful if you’re new to the subject.
For access points, routers and small base station applications that can accommodate external antennas, Pulse Electronics offers a nice range of 4G swivel-blade antennas with SMA connectors (down).
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These tools are a great starting point for selecting the right antennas for your application design, however if you have specific needs and would like to speak to one of our regional technical specialists, click the Ask an Expert button to get in touch.
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