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

Simulation Time

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).