PIFAs in Free Space and Cell Phone
Laptop with an inverted F antenna
Planar Inverted F Antennas in Free Space and Cell Phone
Planar inverted F antennas (PIFAs) are antennas often used in cell phones. This kind of antenna resonates around quarter of used wavelength. It is low profile antenna and it can be easily hidden into the housing of cell phone.
Backward radiation of PIFA can be reduced. In real life, this means that radiation toward cell phone user’s head is lowered (SAR is decreased). It has high gains in both vertical and horizontal polarizations, which is useful if the PIFA position/orientation is changeable.
This paper presents two models of PIFAs, modeled and simulated in free space and in cell phone.
PIFAs in Free Space
Two models of PIFA in free space are created. The first one is PIFA of rectangular shape (Fig. 1) while the other one is curved shape PIFA (Fig. 2).
Fig. 1. Rectangular shape PIFA.
Fig. 2. Curved shape PIFA.
Light blue areas represent metallic parts of the antenna, while the red areas represent dielectric substrate. Both models are created from the scratch in WIPL-D Pro CAD.
Both PIFAs are dual band antennas. They are created in such manner than operating bands are about 0.9 GHz (lower band) and 1.8 GHz (higher band). Since this paper describes an illustrative application, characteristics of PIFAs are not forced to be the same.
PIFAs are simulated in free space. Results (s parameters) are presented in Fig. 3 and Fig. 4.
Fig. 3. PIFAs in lower band – s parameters
Fig. 4. PIFAs in higher band – s parameters
PIFAs in Cell Phone
Model of cell phone is obtained by converting WIPL D Pro CAD phone model to WIPL-D Pro (Fig. 5).
Fig. 5. Cell phone in WIPL-D Pro
PIFAs are converted from WIPL-D Pro CAD to WIPL D Pro and imported in the cell phone WIPL-D Pro model (Fig. 6 and Fig. 7).
Ground plane and electronic devices inside phone are modeled using metallic shape shown in Fig. 6 and Fig. 7. PIFAs’ dielectric substrate is shown here using orange color.
Fig. 6. Rectangular PIFA in cell phone with ground plane and modeled electronic devices inside the phone
Fig. 7. Curved PIFA in cell phone with ground plane and modeled electronic devices inside the phone
PIFAs are simulated in cell phone. Results (s parameters) are presented and compared with results from PIFAs in free space (Fig. 8 and Fig. 9).
Fig. 8. PIFAs in free space and cell phone. Lower band – s parameters
Fig. 9. PIFAs in free space and cell phone. Higher band – s parameters
Radiation Pattern Comparisons
Minimum values of s11 parameter are found for curved and rectangular PIFA, in both lower and higher frequency band. In lower frequency band, rectangular PIFA in cell phone resonates at 910.52 MHz while curved PIFA in cell phone resonates at 896.74 MHz. In higher frequency band, rectangular PIFA in cell phone resonates at 1.79772 GHz while curved PIFA in cell phone resonates at 1.79867 GHz (shown with less decimal digits on markers in Fig. 9).
Radiation patterns for circular and rectangular PIFAs, in free space and in cell phone are presented (Figs. 10-17). Operating frequencies are frequencies where s11 of PIFAs in cell phone models reach for minimal value.
Fig. 10. Rectangular PIFA in free space – radiation pattern at 910.52 MHz
Fig. 11. Rectangular PIFA in free space – radiation pattern at 1.79772 GHz
Fig. 12. Circular PIFA in free space – radiation pattern at 896.74 MHz
Fig. 13. Circular PIFA in free space – radiation pattern at 1.79868 GHz
Fig. 14. Rectangular PIFA in cell phone – radiation pattern at 910.52 MHz
Fig. 15. Rectangular PIFA in cell phone – radiation pattern at 1.79772 GHz
Fig. 16. Circular PIFA in cell phone – radiation pattern at 896.74 MHz
Fig. 17. Circular PIFA in cell phone – radiation pattern at 1.79868 GHz
The most demanding simulation is simulation of quadrilateral PIFA inside the cell phone.
The project requires 29,299 unknowns. It was solved on a computer Intel® Core™ i7 CPU 950 @ 3.07 GHz with 8 GB RAM and GPU card NVIDIA GeForce GTX 470. Total simulation time is about 2 hours for entire frequency range (11 frequency samples).
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