AN2731 Freescale Semiconductor / Motorola, AN2731 Datasheet - Page 19

• Manufacturer Part Number: AN2731
• Description: Compact, Integrated Antennas: Designs and Applications for the MC13191 and MC13192
• Manufacturer: Freescale Semiconductor / Motorola

8.2
Numerous chip antenna designs exist. It is recommended to carefully follow the manufacturers
recommendations regarding ground, keep-out areas, etc. Only one example is shown, indicating that some
tuning will be necessary. The chip antenna, AT9520-B2R4HAAT from ACX, has been mounted on the
board as shown in the following figure.
Without any tuning, the antenna has a resonant frequency at 2.85 GHz and the return loss at 2.45 GHz is
very bad (about –2 dB). The antenna can be tuned either by inserting a chip coil in series with the feed
point, or adding a PCB track to the opposite end to lower the resonant frequency to 2.45 GHz. It turned
out that a tuning coil of 5.6 nH or a PCB track of 6 mm was optimal.
8.3
Two full-size designs have been tested.
The shape assures a reasonable omnidirectional coverage while feeding and matching is done by a hairpin
design. In one particular design, separate TX and RX antennas were placed on top of each other, one on
each side of the PCB. Performance in this design has been adequate. This dipole has also been bent to
improve the omnidirectional characteristics. Impedance match to 200 Ohms is improved by using a folded
design, with uneven track within the antenna. Gerber data is available for both antennas.
Freescale Semiconductor
1. A printed balun and 50 ohm connector for use with the RF Daughter Card, 13192RFC-A00.
2. A printed balun on the MC13192-SARD which is included in the 13192DSK-A00, (Developer’s
Starter Kit).
Chip Antennas
Dipole Antennas
The chip antenna, which is the helix-type, has been mounted perpendicular
to the ground plane and there is considerable clearance around the antenna.
Both factors ensure good efficiency.
Compact Integrated Antennas, Rev. 1.2
Figure 17. Chip Antenna
NOTE
Design Examples
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