AN2731 Freescale Semiconductor / Motorola, AN2731 Datasheet - Page 14

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

Potential Issues
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Numerous things can go wrong with an antenna design. The following list provides a few do’s and don’t’s
which may server as a good checklist in a final design. Many of these items seem obvious to the
experienced antenna designer, but many of these issues are routinely encountered in practice. This is
obviously not a complete list.
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Two antenna designs are employed for the MC13192/93 hardware.
However, most antenna designs are intended to interface with the usual 50 Ohm industrial standard. This
is certainly true for all chip antennas. For interfacing the MC13191/92/93 to a single-ended 50 Ohm
antenna, it has been shown that the smallest and most cost-effective solution are two ceramic baluns and
an RX/TX switch.
The MC13192-EVB, which is included in the MC13193EVK-A00, provides an example of this setup.
Users can omit the RX/TX switch and add two chip antennas, but in most cases the switch is less costly
than another antenna. Any other 50 Ohm, single ended antenna design can be added if required. This
includes among others the F-antenna, monopole, helical, and the usual commercially available chip
antennas. The single-port, 50 Ohm solution has the added advantage that by adding a ceramic bandpass
filter for improved performance is easy. For a very low cost, low bill of materials (BOM) count solution,
users should consider interfacing the antenna(s) directly to MC13191/92/93, and integrate both antennas
and matching components into the PCB.
This setup does have some unique requirements, due to the input/output requirements of the
MC13191/92/93. To achieve a good match to the MC13192/92/93, the antenna should include the
following properties:
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1. Dipole (lowest cost implementation)
2. F-antenna
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Potential Issues
Never place ground plane or tracks underneath the antenna
Never place the antenna very close to metallic objects
Be careful about the wiring in the finalized product, not too close to the antenna
A monopole antenna should have a reasonable ground plane to be efficient
Do the final tuning in the end product, not in free air
Never install a chip antenna in a vastly different layout than the reference design, and expect it to
work without tuning
Do not use a metallic enclosure or metallized plastic for the antenna
Test the plastic casing for high RF losses, preferably before production
Never do a cut and paste antenna design and expect it to work without testing
Never use low-Q loading components, or change manufacturer without retesting
Do not use very thin PCB tracks, the tracks should be fairly wide
Recommended Antenna Designs
Balanced design
Compact Integrated Antennas, Rev. 1.2
Freescale Semiconductor