2.4-GHz Inverted F Antenna (Rev. C)

Application Report
SWRU120C – April 2007 – Revised February 2017
2.4-GHz Inverted F Antenna
ABSTRACT
This document describes a printed-circuit board (PCB) design that can be used with all 2.4-GHz
transceivers and transmitters from Texas Instruments™. The maximum gain is measured to be +3.3 dBi,
and the overall size requirements for this antenna are 25.7 × 7.5 mm. Thus, this antenna is compact, low
cost, and high performance.
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2
3
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Contents
Description of Inverted F Antenna Design ................................................................................ 2
1.1
Implementation of Inverted F Antenna ........................................................................... 2
Results ........................................................................................................................ 3
2.1
Radiation Pattern ................................................................................................... 3
2.2
Reflection ........................................................................................................... 10
2.3
Bandwidth .......................................................................................................... 10
Conclusion .................................................................................................................. 11
References .................................................................................................................. 11
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Description of Inverted F Antenna Design
1
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Description of Inverted F Antenna Design
Because the impedance of the inverted F Antenna (IFA) is matched directly to 50 Ω, no external matching
components are required.
1.1
Implementation of Inverted F Antenna
It is important to make an exact copy of the antenna dimensions to obtain optimum performance. The
easiest approach to implement the antenna in a PCB CAD tool is to import the antenna layout from a
gerber file or a DXF file. Such files are included in CC2430DB reference design [1]. The gerber file is
called Inverted_F_Antenna.spl and the DXF file is called Inverted_F_Antenna.dxf. If the antenna is
implemented on a PCB that is wider than the antenna, avoid placing components or having a ground
plane close to the end points of the antenna. If the CAD tool being used does not support importing gerber
or DXF files, see Figure 1 and Table 1.
Figure 1. IFA Dimensions
Table 1. IFA Dimensions
H1
5.70 mm
W2
0.46 mm
H2
0.74 mm
L1
25.58 mm
H3
1.29 mm
L2
16.40 mm
H4
2.21 mm
L3
2.18 mm
H5
0.66 mm
L4
4.80 mm
H6
1.21 mm
L5
1.00 mm
H7
0.80 mm
L6
1.00 mm
H8
1.80 mm
L7
3.20 mm
H9
0.61 mm
L8
0.45 mm
W1
1.21 mm
Because there is no ground plane beneath the antenna, the PCB thickness will have little effect on the
performance. The results presented in this document are based on an antenna implemented on a PCB
with a 1-mm thickness.
2
2.4-GHz Inverted F Antenna
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Results
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2
Results
All of the results presented in this section are based on measurements performed with CC2430DB [1].
2.1
Radiation Pattern
Figure 2 shows how to relate all of the radiation patterns to the orientation of the antenna. The radiation
patterns were measured with the CC2430 device programmed to 0-dBm output power.
Figure 2. Relating Antenna to Radiation Patterns
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Results
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Figure 3 shows the XY plane vertical polarization.
Figure 3. XY Plane–Vertical Polarization
4
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Results
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Figure 4 shows the XY plane horizontal polarization.
Figure 4. XY Plane–Horizontal Polarization
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Results
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Figure 5 shows the XZ plane vertical polarization.
Figure 5. XZ Plane–Vertical Polarization
6
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Results
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Figure 6 shows the XZ plane horizontal polarization.
Figure 6. XZ Plane–Horizontal Polarization
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Results
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Figure 7 shows the YZ plane vertical polarization.
Figure 7. YZ Plane–Vertical Polarization
8
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Results
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Figure 8 shows the YZ plane horizontal polarization.
Figure 8. YZ Plane–Horizontal Polarization
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Results
2.2
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Reflection
Figure 9 shows that the IFA ensures less than 10% reflection of the available power for a bandwidth of
more than 300 MHz. A large bandwidth makes the antenna less sensitive to detuning because of plastic
encapsulation or other objects in the vicinity of the antenna.
Figure 9. Measured Reflection at Feed Point of Antenna
2.3
Bandwidth
Another way of measuring the bandwidth after the antenna is implemented on a PCB and connected to a
transmitter is to write test software that steps a carrier across the frequency band of interest. By using the
maximum hold function on a spectrum analyzer, the variation in output power across frequency can easily
be measured.
10
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Conclusion
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Figure 10 shows how the output power varies on the IFA when the PCB is horizontally oriented and the
receiving antenna has horizontal polarization. This measurement was not performed in an anechoic
chamber, thus the graph shows only the relative variation for the given frequency band.
Figure 10. Bandwidth of IFA
3
Conclusion
The PCB antenna presented in this document performs well for all frequencies in the 2.4-GHz ISM band.
Except for two narrow dips, the antenna has an omni directional radiation pattern in the plane of the PCB.
These properties will ensure stable performance regardless of operating frequency and positioning of the
antenna. Table 2 lists the most important properties for the IFA.
Table 2. Summary of IFA Properties
Gain in XY plane
1.1 dBi
Gain in XZ plane
3.3 dBi
Gain in YZ plane
Reflection
Antenna size
4
1.6 dBi
< –15 dB
25.7 × 7.5 mm
References
1. CC2430DB Reference Design
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Revision History
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Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from B Revision (April 2008) to C Revision .................................................................................................... Page
•
•
12
Changed +3.3 dB to be +3.3 dBi ........................................................................................................ 1
Changed dB in Table 2 to dBi .......................................................................................................... 11
Revision History
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