Radio Transmitter & Receiver Modules
Antenna Design
T6 / R6
The design and positioning of the antenna is as crucial as the module performance itself in achieving a good
wireless system range. The following will assist the designer in maximising system performance.
The antenna should be kept as far away from sources of electrical interference as physically possible. If
necessary, additional power line decoupling capacitors should be placed close to the module.
The antenna ‘hot end’ should be kept clear of any objects, especially any metal as this can severely restrict
the efficiency of the antenna to receive power. Any earth planes restricting the radiation path to the antenna
will also have the same effect.
Best range is achieved with either a straight piece of wire, rod or PCB track @ ¼ wavelength. Further range
may be achieved if the ¼ wave antenna is placed perpendicular in the middle of a solid earth plane
measuring at least 16cm radius. In this case, the antenna should be connected to the module
via some 50 ohm characteristic impedance coax.
Loop Antenna
Loop Antenna Area
600mm
2
PIN 1
PIN 2
C1
C1 = 1pF @ 433MHz
C1 = 1pF @ 868MHz and halve loop area
Loop Antenna:
The loop antennae, is the
cheapest and most compact of the three
antennas. The antenna always takes up the
form of a track on a PCB, the antenna consists
of a feeder capacitor C1 which is connected
directly to the transmit pin on the radio module,
and a loop track which is grounded. This
antenna gives the poorest performance of the
three, and thus is essential that the tuning
capacitors are adjusted for the best system
performance.
Helical Antenna
RF
Helical Antenna:
The helical antenna provides
a more compact antenna for mobile radio
systems. The antenna must be connected
directly to the transmit pin of the radio module.
20mm @ 868MHz
∅
= 5mm (inside)
Whip Antenna
PIN 1
7cm @ 868MHz
Whip Antenna:
The whip antenna simply consists
of a metal rod with a length of ¼ of the wavelength
of the signal which you wish to transmit. The whip
must be directly connected to the transmit pin on
the module.
DS306-3
May 03
2003
REG No 277 4001, England.
Page 6
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