Depending on the application and bearing in mind applicable legal requirements (see p.11), a
variety of antenna types may be used with the TX3A and RX3A.
Integral antennas
generally do not perform as well as externally mounted types, however
they result in physically compact equipment and are the preferred choice for portable
applications. The following can be recommended:
Whip (¼-wave).
This consists simply of a piece of wire or rod connected to the module at one
end. The lengths given below are from module pin to antenna tip including any
interconnecting wire or tracking. This antenna is quite simple and performs well, especially if
used in conjunction with a ground plane. This will often be provided by the PCB on which the
module is mounted, or by a metal case.
Base-loaded whip.
This is a shortened whip, tuned by means of a coil inserted at the base.
This coil may be air-wound for maximum efficiency, or a small SMT inductor can be used if
space is at a premium. The value must be carefully chosen to tune the particular length of
whip in use, making this antenna more difficult to set up than a ¼-wave whip.
Helical.
This is a compact but slightly less effective antenna formed from a coil of wire. It is
very efficient for its size, but has high Q and tends to suffer badly from detuning caused by
proximity to nearby conductive objects. It needs to be carefully trimmed for best performance
in a given situation and the required dimensional tolerances can be difficult to achieve
repeatably, nevertheless it can provide a very compact solution.
Loop.
A loop of PCB track, tuned and matched with 2 capacitors. Loops are relatively
inefficient but have good immunity to proximity detuning, so may be preferred in shorter
range applications where very high component packing density is necessary.
L
RF
1/4-wave whip
wire, rod, PCB track
or a combination of these
L (mm) = 71250 / freq(MHz)
RF
Base-loaded whip
shortened wire, rod, PCB track etc.
with loading coil.
SMT inductor may be used if reqd.
RF
Helical
RF
wire spring, dia 3mm approx.
trim wire length, number of turns
and turns spacing for best results
C
match
C
tune
RF-GND
track width = 1mm
2
area 100 - 400 mm
capacitors 0.5-5pF variable or fixed
(values depend on loop dimensions)
Loop
Fig.8: Integral antenna configurations
Radiometrix Ltd, TX3A & RX3A Data Sheet
page 10
RADIOMETRIX [ RADIOMETRIX LTD ]
