DN007 - 2.4 GHz Inverted F Antenna (Rev. B

Application Reports

REGULATIONS, FCC, ETSI, ARIB, SWRU120B, SWRU120

Texas Instruments, Incorporated [SWRU120,B]

Antenna Specification

Electronic Silk Road (Shenzhen) Tech Co., Ltd 2K615 2APEW-2K615 2APEW2K615 2k615

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Document DEVICE REPORTGetApplicationAttachment.html?id=7632501 
2.4 GHz Inverted F Antenna
Keywords

By Audun Andersen

· CC2400 · CC2420 · CC2430 · CC2431 · CC2500 · CC2510 · CC2511

· CC2550 · CC2520 · CC2480 · PCB Antenna · 2.4 GHz · Inverted F Antenna

Manufacturer: Texas Instruments Address: 16th and 17th floor, Building T8, Qian Hai Kerry Business Center, Qianhai Shenzhen-Hongkong Cooperation Zone, Shenzhen

Frequency Range: 2400~2500MHz Max Gain: 2.2dBi

1 Introduction
This document describes a PCB antenna design that can be used with all 2.4 GHz transceivers and transmitters from Texas Instruments.

2 Abbreviations

CC2480 EM IFA ISM PCB

Z-Accel ZigBee Processor Evaluation Module Inverted F Antenna Industrial, Scientific, Medical Printed Circuit Board

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3 Description of the Inverted F Antenna Design
Since the impedance of the Inverted F Antenna is matched directly to 5 0 ohm no external matching components are needed.
3.1 Implementation of the 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 either a gerber or DXF file. Such files are included in CC24 3 0 DB 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 it is important to avoid placing components or having a ground plane close to the end points of the antenna. If the CAD tool being used doesn't support import of gerber or DXF files, Figure 1 and Table 1 can be used.

Figure 1. IFA Dimensions

H1

5.70 mm W2

0.46 mm

H2

0 . 7 4 mm L1

2 5 . 5 8 mm

H3

1 .2 9 mm L2

16 . 4 0 mm

H4

2 .2 1 mm L3

2 . 1 8 mm

H5

0 . 6 6 mm L4

4 . 8 0 mm

H6

1 .2 1 mm L5

1 .0 0 mm

H7

0 . 8 0 mm L6

1 .0 0 mm

H8

1 .8 0 mm L7

3 . 2 0 mm

H9

0 . 6 1 mm L8

0 . 4 5 mm

W1

1.21 mm

Table 1. IFA Dimensions
Since there is no ground plane beneath the antenna, PCB thickness will have little effect on the performance. The results presented in this design note are based on an antenna implemented on a PCB with 1 mm thickness.

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4 Results
All results presented in this chapter are based on measurements performed with CC2430DB [1]. 4.1 Radiation Pattern Frequency: 2440MHz Unit: dBi
Max Gain: 2.2dBi
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4.2 Reflection
Figure 9. Measured Reflection at the Feed Point of the Antenna Figure 9 show 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 due to plastic encapsulation or other objects in the vicinity of the antenna. 4.3 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 " Max hold" function on a spectrum analyzer the variation in output power across frequency can easily be measured. Figure 1 0 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.
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Bandwidth IFA

2.4

2.4835

0

- 10

-20

Output pow er

-30

Low er band edge

Upper band edge

-40

-50

-60

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Frequency [ GHz]

Figure 10. Bandwidth of IFA

5 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 inverted F antenna.

Gain in XY Plane Gain in XZ Plane Gain in YZ Plane Reflection Antenna Size

2.2dB 1.2 dB 1.6 dB
< - 15 dB
25.7 x 7.5 mm

Table 2. Summery of the Properties of the IFA

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6 References
[1] CC2430DB Reference Design (swrr034.zip)
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7 General Information

7.1 Document History

Revision SWRU12 0 B SWRU12 0 A SWRU12 0

Date 2008-04-04 2008-02-28 2007-04- 16

Description/ Changes Renamed CCZACC0 6 to CC2 4 8 0 Added reference to CCZACC0 6 and CC2 5 2 0
Initial release

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