6 LPWAN Antenna Placement Tips for Optimal Range
When it comes to radio communications, antennas are a powerful component we can use to improve signal propagation and coverage. An antenna is a specialized transducer that converts radio frequency (RF) fields into alternating current or vice versa. Antennas can transmit and/or receive radio signals. Proper antenna setup and installation can drastically improve radio transmission distance and penetration capability. If you’re planning to deploy LPWAN for long-range applications, here are 6 LPWAN antenna placement best practices to consider.
1. Choose the Right Antenna Size
Ideally, the antenna length should be equivalent to the wavelength of a signal. However, this is often not practical given the very long wavelength of LPWAN signals. As a rule of thumb, antenna size of ½ or ¼ wavelength will produce good results.
The wavelength (m) is calculated as v/f where v is the wave speed (m/s) and f is the frequency (Hz). In the air, electromagnetic waves travel at the speed of light, which is approximately 300,000,000 m/s. That means the LPWAN wavelength at 915 MHz (North America) is 32.76 cm and as such, desirable antenna lengths are 16.38 cm and 8.19 cm, respectively. Similarly, recommended antenna sizes for LPWAN operation at 868 MHz (Europe) are 17.27 cm and 8.63 cm.
2. Select the Right Antenna Type
Antennas are broadly categorized into two types: omnidirectional and directional. Omni-directional antennas radiate or receive equal radio power in all horizontal directions, forming a donut-shaped radio pattern. The antenna resides at the center of the donut. On the other hand, directional antennas radiate or receive greater radio power in a specific direction. A typical example is the Yagi antenna.
Given the inherent trade-off between utility and signal power, the choice of antenna type typically depends on your network and applications. Omnidirectional antennas offer ease of installation and greater flexibility in terms of device and gateway locations. Therefore, they are ideal for LPWAN gateways that need to pull data from numerous nodes at all directions. These antennas are also used in applications with moving end devices and when transmission directions should be flexible.
If your transmitter and gateway are fixed and the direction of data communications is well defined, you may want to consider a directional antenna like the Yagi. Compared to omnidirectional antennas, directional antennas offer much better signal strength. This is because the transmission energy is concentrated in one direction rather than distributed all around. As such, unwanted interference can be reduced, and less energy is required for better signal strength. On the flip side, they are more complex to install.
3. Optimize Line-of-Sight
As obvious as it sounds, the importance of line-of-sight – or optical visibility between transmitter and receiver antennas – may sometimes be overlooked. Radio waves lose signal strength when traveling through dense materials, which explains why LPWAN performance in rural and urban areas greatly differ. Physical obstructions such as buildings, hills, walls, and metal blocks, absorb and/or reflect/refract the RF signal, thereby reducing range.
In structurally dense environments, line-of-sight can be achieved by increasing the height of the gateway antenna, the transmitter antenna or both. Furthermore, the use of an external outdoor antenna, particularly at the gateway, considerably improves line-of-sight and signal reception. Elevating the outdoor receiver antenna above all obstacles (e.g. installing the antenna on a rooftop or tower) is the most practical way to improve the range of an entire network.
4. Clear Obstacles in the Antenna Vicinity
Walls, electrically conducting objects and electronic devices (e.g. PC, monitor, LED lighting…) located in the immediate vicinity of an antenna “detune” and degrade its performance. For the transmitter antenna, these obstacles absorb power from the radiation field, thereby decreasing the effective transmission power and operating distance. For the receiver antenna, they influence its directivity and raise the noise level.
While the absolute minimum distance is 6 cm, a common best practice is maintaining at least 70 cm distance between antennas and any obstacles. External antennas must be mounted on a pole rather than at the side of a building.
Transmitting equipment (e.g. mobile phones, wireless headphones) should be completely avoided in the vicinity of the receiver antenna, as they can cause radio interference and intermodulation.
5. Orient the Antenna Properly
Accurate antenna orientation is vital to ensure maximum coverage. Due to variation in radiation patterns, different antenna types should be oriented differently. For example, omnidirectional antennas should be oriented vertically to obtain the best range. If the antenna must be placed horizontally, it should not be directed at the receiver. Yagi antennas, on the other hand, should be mounted horizontally pointing in the direction of its counterpart.
Also, make sure that the polarization of the receiver antenna matches that of the transmitter antenna to optimize signal reception. Polarization refers to the direction of the radio waves produced by the antenna. For example, if you use a vertically polarized, omnidirectional antenna at the gateway and a Yagi antenna at the transmitter, the Yagi antenna should be mounted horizontally with its elements in the vertical position for vertical polarization.
6. Use Low-Loss Connectors and Cables
When installing external, outdoor antennas, the use of any extension cables reduces signal strength to some extent. Selecting high-quality connectors and cables with optimal insulation and shielding can help minimize signal losses in the material. On top of that, the length of the cable should be kept as short as possible to circumvent extra losses.
While there are multiple factors that influence the range performance of a radio link, appropriate antenna size, type and placement are key to obtain the best network coverage and deep penetration capability of LPWAN signals.
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