concluded that there is large combinations (ideally n P n , here n ϭ 6, the number of shorting straps) of the frequency tuning of the PIFA. A log circuit loaded with the appropriate algorithm can handle such a sequential operation.
Radiation Pattern of PIFAThe radiation measurements were conducted at Nanyang Technological University's Anechoic Chamber. The RF switches are supplied with a Ϯ5-V DC bias voltage source. Figure 9 shows the copolar (solid line) and crosspolar (dotted line) E-and H-plane radiation patterns at 1.9 GHz, respectively. Both copolar and crosspolar E-and H-plane radiation patterns yield very wide beamwidth, except for the single directional distortions in the patterns. The front-to-back radiation ratio is about 10 dB, which is good for users with lower radiation absorption in brain tissues. This may be due to the finite ground plane of the PIFA and the parasitics of the RF switches. Similar radiation patterns are obtained at the lower frequency band.
CONCLUSIONThe design and development of a shorting-strap tunable single-feed dual-band stacked-patch PIFA have been presented. RF switches were integrated to one side of the PIFA's shorting straps to design a frequency-agile antenna in a compact package. The tunable PIFA yielded 13% frequency tunability BW at the 900 MHz band and 21% BW at the 1.9-GHz band. The measured radiation patterns are fan shaped with lower backlobes, as compared to those of the standard PIFA. Because there are many applications associated within the frequency band of 800 -2000 MHz, it is highly desirable to have a single antenna cover all applications in an integrated electronic gadget. Finally, the presented antenna's performance is very promising for present and future wideband applications.
ACKNOWLEDGMENTThe final-year-project students working on tunable PIFA helped in the fabrication and measurement of the antenna.
INTRODUCTIONDue to the widespread use of personal communications systems, much public concern has arisen about the possible dangerous effects of electromagnetic radiation on human health, stemming mainly from mobile telephones and base-station antennas. For this reason, many countries have adopted guidelines for limiting that exposure [1, 2] by defining "reference levels" in terms of electric and magnetic field strengths, E and H, and equivalent plane-wave power density. Field-strength limits can be exceeded if compliance can be shown with respect to "basic restrictions" in terms of specific absorption rate (SAR) limits [1].In the operational environment of a base-station antenna, the presence of scatters does not allow the use of an equivalent free-space formulation. The fields in a given region may appear due to direct illumination from the antenna, and reflections and diffractions by obstacles nearby. In a previous work [3], the TDPO technique, which can be improved by the physical theory of diffraction in combination with the FDTD method, has been used to calculate the energy absorbed by a human head exposed to an electromagnetic field in the presence...
