9.4 ANTENNAS, COAX FEEDERS & PERIPHERALS
9.4.1
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.
9.4.2
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
Helical
-3dB
Vertical
In-house testing and local use
End Fed Dipole
0dB
Vertical
Folded Dipole
0dB
Vertical/Hor
izontal
Local Scanner or Multi-point system
6dB Co-linear
+6dB
Vertical
3dB Co-linear
+3dB
Vertical
Wide area Scanner
12 Element
Yagi
+12dB
Vertical/Hor
izontal
4 Element Yagi
+8dB
Vertical/Hor
izontal
Outstation or point to point link
Corner
Reflector
+10dB
Vertical/Hor
izontal
Outstations in areas of bad Interference or where
radiation must be kept to a minimum
Patch Antenna
0dB
Vertical/Hor
izontal
Kiosk or Wall mounting
9.4.3
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
vertical (vertically polarised) or horizontal (Horizontally polarised) but communicating products should
be fitted with antennas of the same orientation, if not a loss of signal strength will occur. Vertical and
horizontal propagation can be very useful on single or repeater sites where isolation is required between
communication paths. Using polarised antennas for each path will increase the isolation which will
reduce possible interference.
9.4.4
OMNI-DIRECTIONAL ANTENNAS
With approximately 360 degree radiation pattern, this type of antenna is ideal for a scanning station or
where communication to a group of widely dispersed outstations is required.
9.4.5
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
URT500 Manual
Page 37 of 42
Rev. C – 6 August 2008
