Radio signals are transmitted and received using an antenna. An antenna can be mounted vertically, horizontally, diagonally, or in a combination of orientations.

Essentially, the orientation of the transmitter and receiver must match in order to get the best possible signal. For every degree of separation that the transmitter and receiver are out of alignment, signal loss and noise start to occur within your datalink.

For the best possible datalink, you will want the strongest signal with the least amount of interference (noise) – this is referred to as the Signal-to-Noise ratio (or SNR). The higher the SNR, the better.

A vertically polarised antenna at the transmitter communicating with a vertically polarised antenna at the receiver will provide a good, clear signal. Lots of signal, low background noise.

A vertically polarised antenna at the transmitter communicating with a 45° slant polarised antenna at the receiver will provide a poor signal.

A vertically polarised antenna at the transmitter communicating with a horizontally polarised antenna at the receiver will provide no signal.

The antenna images above are for illustrative purposes only. It should be noted that antennas can be electrically polarised in a different orientation to their physical appearance. For example, the new Wave Relay ANT-2037 horizontally polarised antenna is physically vertical in appearance but transmits and receives an electrically horizontally-polarised signal.

Wave Relay ANT-2037 Horizontally Polarised

Wave Relay ANT-2005 Vertically Polarised

Why not have all three antenna always vertically polarised then?

Because there are lots of environmental and other unseen RF interference’s operating in the same frequency space as the transmitter and receiver over which you have no control. This interference is inevitable and not something that can be easily prevented. RF airspace rarely exclusive, and you are likely to have to share your RF space with other users, such as mobile phone network operators, TV broadcast operators, WIFI hotspots, etc. Just like your own datalink, these other RF signals will have a polarity – some will be vertical, some horizontal, some diagonal, and various degrees of separation and combinations of each.

The interference is likely to differ in each and every scenario. In some environments, vertically polarised antenna might be more susceptible to interference than horizontally polarised ones (because there might potentially be lots of other vertically polarised transmitters & receivers within the local vicinity, for example).

What is antenna diversity and how does it help?

The Wave Relay® MPU5 radio has three antenna ports. These antenna ports can be used to connect different polarity antenna giving your data the best possible chance of reaching its destination.

The Wave Relay® MPU5 radio in this image is fitted with two ANT-2005 vertically-polarized antennas, whilst the centre antenna has been replaced with an ANT-2037 horizontally-polarized antenna.

Because the Wave Relay® MPU5 makes use of spatial multiplexing and space-time block coding MIMO techniques, the same data is sent three times (once per antenna) and re-assembled at the receiving end of the datalink.

If there is interference on the horizontally-polarised antenna, data sent via the vertically-polarised antenna still has a very good chance of being received.

In field tests, having an antenna combination such as this has proven to almost double the bandwidth of the datalink.

Note that the two ANT-2005 antennas aren’t entirely vertical, but slanted. Again, this antenna diversity lessens the chance of interference, and increases the signal-to-noise ratio.

Make use of antenna diversity in your MANET network design to optimise it for best performance.