A wireless network always consists of several components. The central one is the wireless router. When selecting the router, it is important that it has the quality and performance required for the individual application, i.e. that it has enough integrated wireless modules and the necessary routing performance. It is also clear that the device must be configured in the best possible way.
A wireless router also needs antennas, of course. However, these are often the components in the network to which too little attention is paid - even the best router with an optimal configuration cannot compensate for incorrectly selected or placed antennas, and the network quality is and remains inadequate. Therefore, it is elementary to select antennas with the appropriate functions (MIMO or multiple 4G, 5G , WLAN, GNSS, etc.), the correct frequency ranges, sufficient power, optimal mounting type (design), as well as cable qualities and connectors suitable for the respective frequency ranges in terms of attenuation and crosstalk (shielding effectiveness).
First things first
When selecting the right antenna, the general formula "bigger and more expensive equals better" does not apply. Rather, it depends primarily on the individual application and place of use. Therefore, it is important to answer the following questions before purchasing:
- Which technologies should be used - e.g. 5G/LTE, WLAN or GNSS?
- How many modems will be used, respectively how many antennas are necessary (MIMO)?
- How and where should routers and antennas be mounted - indoors or outdoors?
- What is the distance between router and antennas?
- How large must the range or coverage be?
- Where to transmit and receive - in the countryside, where network coverage is rather poor, or in a city?
- Does the application have to comply with certain standards, e.g. for fire protection, road traffic (E1) or railway (EN 50155)?
Cable lengths are a stumbling block
It is essential to clarify where exactly the router and antennas are to be placed. It is important to choose an optimal antenna position close to the router and with as little shadowing as possible - e.g. not under a car seat, behind metal doors, etc.
After the placement issue is resolved, the required cable lengths are determined. Generally, it is said that a length depending on the cable quality and the highest usable frequency range of 3 meters (from approx. 2 GHz) and approx. 5 meters (up to approx. 2 GHz) is reasonable. Anything beyond this entails considerable losses, which is why special low-loss extension cables with attenuation values of < 0.2 dB/m must be used between the antenna (with short cable) and the router. With this, total cable lengths of over 10 meters can be realized. If the distances become too big, the losses become too great and thus the connection poor. Then a wireless solution is no longer appropriate, and cables must be used.
Combined antennas: Useful?
If different radio technologies are to be used, e.g. LTE and GNSS, you can choose combined antennas for this purpose – such antennas that combine several in one housing.
The advantages of combined antennas are quick, inexpensive installation, little interference with the bodywork of vehicles or the housing of equipment (especially in the case of leased vehicles and equipment), and equal cable lengths.
However, there may also be disadvantages. Depending on the arrangement of the antenna radiators, there may be interference and thus a limitation of the usable bandwidth. This can also interfere with navigation antennas. But: Single antennas only have an advantage over combination antennas here if they are each mounted at a distance of more than 30 cm from each other - the greater this distance, the better.
A special case is WLAN in a vehicle: Because the mobile radio antenna of the router should always be mounted outside the vehicle, a combined mobile radio/WLAN antenna on the roof of an emergency vehicle or a train cannot provide the desired performance, e.g., to supply emergency personnel or passengers in, or around, the vehicle with WLAN. In these cases, it makes sense to separate the antennas and install the WLAN antenna in or on the sides of the vehicle - i.e., where the WLAN is ultimately to be used.
Conclusion
In summary, it can be stated that the functioning of an antenna is strongly influenced by its environment. The aim must therefore be to design this environment as optimally as possible in order to achieve the best possible transmission performance. The overall system of antenna, connecting line and router must always be kept in mind.
In addition, it is important to consider whether and which legal standards, such as road traffic or fire protection standards, may have to be met - both by the router and the antennas.
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