WSN Manual
Page 31 of 34
Rev. G
– 4 March 2007
7.4 ANTENNAS, COAX FEEDERS & PERIPHERALS
7.4.1
Antennas
Apart from the radio modem, the antenna is probably the most important part of the system. The
wrong choice or a bad installation will almost certainly impede the product’s performance.
Depending on the application either an omni-directional or directional antenna will be required.
7.4.2
Types of Antennas
We can offer a complete range of antennas to suit all applications; details of some of the more
popular ones are outlined below:-
Antenna Types
Typical
Gain
Polarisation
Use
Vertical Whip
0dB
Vertical
In-house testing and local use
Helical
- 3dB
Vertical
End Fed Dipole
0dB
Vertical
Local Scanner or Multi-point system
Folded Dipole
0dB
Vertical/Horizontal
6dB Co-linear
+6dB
Vertical
Wide area Scanner
3dB Co-linear
+3dB
Vertical
12 Element Yagi
+12dB
Vertical/Horizontal
Outstation or point to point link
4 Element Yagi
+8dB
Vertical/Horizontal
Corner Reflector
+10dB
Vertical/Horizontal
Outstations in areas of bad
Interference or where radiation must
be kept to a minimum
Patch Antenna
0dB
Vertical/Horizontal
Kiosk or Wall mounting
7.4.3
Directional Antennas
For point-to-point communications, a directional Yagi or corner reflector is probably the best
type of antenna to use, as directional antennas provide relatively high gain in the forward
direction within a limited beamwidth and very good rejection of unwanted signals at the rear.
The number of elements and hence the size, will depend on the gain and beam width required.
Yagi antennas can be used in the vertically polarised or horizontally polarised, but
communicating products should be fitted with antennas of the same polarisation. If not a loss of
signal strength will occur. Use of both vertical and horizontal propagation can be very useful on
single or repeater sites where isolation is required between communication paths. Using
differently polarised antennas for each path will increase the isolation, which will reduce
possible interference between the paths.
7.4.4
Omni-Directional Antennas
With approximately 360-degree radiation pattern, this type of antenna is ideal for the central site
of a scanning station or where communication to a group of widely dispersed outstations is
required.
7.4.5
Patch or Plate Antennas
The patch or plate antennas are normally rectangular or round, with a back plate of aluminium
or stainless steel. A polycarbonate or ABS cover is fitted to protect the antenna from the
environment. This type of antenna can be produced in different sizes with various radiation
patterns to suit the application. Depending on the construction and radiation pattern, the gain is
usually between -3dB to + 3dB. Their use is very popular on roadside kiosks, buses, trains,
aircraft, or where covert communication is required.
