When deploying BlueZoo sensors, your antenna selection can significantly impact the accuracy and range of your data collection. While the sensors’ internal antennas work well for most applications, external antennas allow non-spherical detection zones to be defined and are important (even for spherical detection zones) when the sensor is inside a metal box.
Internal vs. External antenna sensors
Both the internal-antenna and external-antenna versions of the BlueZoo sensor have two dipole antennas on the printed circuit board (PCB) at a 90-degree angle. On the PCB of the BlueZoo sensor with external antenna connectors, these on-PCB antennas are electrically isolated. See them at the bottom left and bottom right of the PCB in the photo below.
External antenna connectors
The version of the BlueZoo sensor with connectors for two external antennas is delivered with two 2dbi-gain omnidirectional dipole antennas which connect to the sensor’s two female reverse-polarity Sub-Miniature-A (RP-SMA) connectors. These connectors and corresponding coaxial cables are an industry standard.
Orientation of Dipole Antennas
Despite the marketing photo shown below, you will generally want to position the antennas so that they are at right angles to each other, just as the on-PCB antennas are at right angles to each other. This orientation accommodates the donut-shaped gain pattern of a dipole antenna (see explanation below), making the two antennas more effectively represent an omni-directional pattern. This orientation also better accommodates diverse polarization of smartphones used by consumers.
Antennas can be directly connected to the sensor or through a coaxial cable. While it is slightly preferable to use two antennas, it is fine to run the sensor with only one.
You need to be sensitive to two factors: Faraday cages and antenna radiation patterns.
Faraday Cages
A “Faraday cage” is a volume that is surrounded by a conductive surface, usually metal. Metal enclosures can greatly attenuate the propagation of electromagnetic radiation including microwaves in the frequencies (e.g. 2.4GHz) used by Wi-Fi radios. The canonical Faraday cage is a box covered in sheet metal. The Faraday cage effect also manifests itself when a conductive surface (e.g. metal sheet or plate) is interposed between a transmitter and a receiver. The presence of this conductive surface can significantly attenuate the strength of microwaves, causing a smartphone to appear further from the BlueZoo sensor than is actually the case. Most advertising panels place their electronics inside a metal box.
For this reason, we recommend that BlueZoo customers which mount the BlueZoo sensor inside a metal box place an external antenna on top of the box to provide an unobstructed microwave view of smartphones.
Dipole Antenna Patterns
The “radiation pattern” of a dipole antenna is like a “donut” that encircles the dipole. In the drawing below, the dipole antenna is vertical and the donut wraps around it. More information on Wikipedia
If you have two antennas positioned vertically, you will get a sensing area that will be flatten at the bottom and the top; this is best when you have floors below or above the level the sensor is placed--and that you don’t want to count the traffic at these different floors. That said, floor in commercial buildings generally incorporate metal plates (forming a Faraday cage) so the benefits of two antennas, one vertical and one horizontal, may outweigh the benefit of a flattened sphere.
As mentioned earlier, if you want a more spherical detection zone, then you should have antennas positioned orthogonally (one being perpendicular to the other, i.e. one vertical, one horizontal).
The two 2dbi external dipole antennas provided with our external-connector sensors can be replaced by antennas with a higher gain or other types of antennas (e.g. an outdoor dome antenna such as the one featured below), many of which are themselves dipole antennas.
Non-omnidirectional antennas
It is also possible to use directional antennas with the BlueZoo external connector sensors. While an omnidirectional antenna represents a spherical detection zone, a directional antenna defines a conical detection zone.
If you use directional antennas, you will want to use only a single antenna. You should never use one directional antenna along with an omnidirectional antenna.
While the most common omni-directional antenna technology is a “dipole antenna”, there are many technologies for directional antennas. BlueZoo directional antennas are either “panel” or “patch” antennas. Directional antennas used for telecommunication purposes are often either Yagi or dish antennas.
If you use a directional antenna to define a conical detection zone and want to use a Wi-Fi Internet backhaul, you will almost certainly need to add a USB Wi-Fi dongle so your Internet connection is not constrained by the directional antenna coverage. The following photo shows a panel antenna connected via RP-SMA directly to a BlueZoo sensor, where the sensor has a second Wi-Fi radio with embedded dipole antenna (the “nano” form factor) connected via the sensor’s USB-A port.
Contact our team if you need an advice or have any questions.
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