Texas Instruments | 2.4-GHz Inverted F Antenna (Rev. D) | Application notes | Texas Instruments 2.4-GHz Inverted F Antenna (Rev. D) Application notes

Texas Instruments 2.4-GHz Inverted F Antenna (Rev. D) Application notes
Application Report
SWRU120D – April 2007 – Revised January 2019
2.4-GHz Inverted F Antenna
ABSTRACT
This document describes a printed-circuit board (PCB) antenna design that can be used with all 2.4-GHz
transceivers and transmitters from Texas Instruments™. The maximum gain when used on the reference
board is measured to be +3.3 dBi, and the overall size requirements for this antenna are 25.7 × 7.5 mm
(not including ground plane).
1
2
3
4
Contents
Description of the antenna Design ........................................................................................ 2
Measurement Results ....................................................................................................... 3
2.1
Radiation Pattern ................................................................................................... 3
2.2
Reflection ........................................................................................................... 10
2.3
Bandwidth .......................................................................................................... 11
Conclusion .................................................................................................................. 11
References .................................................................................................................. 11
Trademarks
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All other trademarks are the property of their respective owners.
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1
Description of the antenna Design
1
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Description of the antenna Design
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.
The antenna impedance is tuned to 50 ohm on the reference board. The impedance will however be
affected by different size and shape of the ground plane, objects in the antenna nearfield such as
mechanical assemblies (housing, batteries, etc.), PCB thickness, PCB material and so on. It is therefore
recommended to add a pi-network close to the antenna feedpoint for impedance matching.
The results presented in this document are based on an antenna implemented on a PCB with a 1-mm
thickness using standard FR-4 material.
Figure 1. IFA Dimensions
Table 1. IFA Dimensions
2
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
2.4-GHz Inverted F Antenna
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Measurement Results
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2
Measurement Results
All of the results presented in this section are based on measurements performed with the CC2430DB [1]
evaluation board.
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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Measurement Results
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Figure 3 shows the XY plane vertical polarization.
Figure 3. XY Plane–Vertical Polarization
4
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Measurement Results
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Figure 4 shows the XY plane horizontal polarization.
Figure 4. XY Plane–Horizontal Polarization
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Measurement Results
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Figure 5 shows the XZ plane vertical polarization.
Figure 5. XZ Plane–Vertical Polarization
6
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Figure 6 shows the XZ plane horizontal polarization.
Figure 6. XZ Plane–Horizontal Polarization
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Measurement Results
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Figure 7 shows the YZ plane vertical polarization.
Figure 7. YZ Plane–Vertical Polarization
8
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Figure 8 shows the YZ plane horizontal polarization.
Figure 8. YZ Plane–Horizontal Polarization
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9
Measurement 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
10
2.4-GHz Inverted F Antenna
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Measurement Results
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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.
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 C Revision (February 2017) to D Revision ............................................................................................. Page
•
•
12
Update was made in the Abstract of this document. ................................................................................. 1
Update was made to Section 1. ......................................................................................................... 2
Revision History
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