CC2400-RTR1 datasheet(57/84 Pages) TI2

57 / 84 page

CC2400

SWRS042A

Page 57 of 83

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).

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