CC2400_08 Datasheet, PDF (57/84 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
48 Antenna Considerations
CC2400 can be used together with various
types of antennas. A differential antenna
like a dipole would be the easiest to
interface not needing a balun (balanced to
un-balanced transformation network).
The length of the λ/2-dipole antenna is
given by:
L = 14250 / f
where f is in MHz, giving the length in cm.
An antenna for 2450 MHz should be 5.8
cm. Each arm is therefore 2.9 cm.
Other commonly used antennas for short-
range communication are monopole,
helical and loop antennas. The single-
ended monopole and helical would require
a balun network between the differential
output and the antenna.
Monopole antennas are resonant
antennas with a length corresponding to
one quarter of the electrical wavelength
(λ/4). They are very easy to design and
can be implemented simply as a “piece of
wire” or even integrated into the PCB.
The length of the λ/4-monopole antenna is
given by:
L = 7125 / f
where f is in MHz, giving the length in cm.
An antenna for 2450 MHz should be 2.9
cm.
Non-resonant monopole antennas shorter
than λ/4 can also be used, but at the
expense of range. In size and cost critical
applications such an antenna may very
well be integrated into the PCB.
Enclosing the antenna in high dielectric
constant material reduces the overall size
of the antenna. Many vendors offer such
antennas intended for PCB mounting.
Helical antennas can be thought of as a
combination of a monopole and a loop
antenna. They are a good compromise in
size critical applications. But helical
antennas tend to be more difficult to
optimize than the simple monopole.
Loop antennas are easy to integrate into
the PCB, but are less effective due to
difficult impedance matching because of
their very low radiation resistance.
For low power applications the differential
antenna is recommended giving the best
range and because of its simplicity.
The antenna should be connected as
close as possible to the IC. If the antenna
is located away from the RF pins the
antenna should be matched to the feeding
transmission line (50 Ω).
SWRS042A
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