**3.2 Meandered PIFA design**

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

**3. Design of general printed-F antenna (PIFA)**

The printed inverted-F antenna (PIFA) is one of common planar antennas used in the commercial and medical devices because of its small size, low profile and low cost [13–20]. The typical PIFA structure is shown in **Figure 4**. Its working principle is same as monopole antenna with quarter-wave long along the main resonant line in **Figure 4**, therefore, the size of the ground plane is also an important part of antenna. It has a shorting feed point at the end of the main resonant line. This folded part introduces capacitance to the input impedance of the PIFA which is canceled by the shorting feed point. This foldable part, therefore, reduces the

*(a) Sinusoidal current distribution for L = 0.5*λ *1. (b) Triangular current distribution for L = 0.1*λ *2 [9].*

**3.1 Printed inverted-F antenna (PIFA)**

**52**

antenna size.

**Figure 3.**

**Figure 4** shows a typical PIFA structure on a printed circuit board (PCB) which is indicated with the dotted area at the PCB upper layer. Meandering line is commonly used to increase the total length in antenna design. The meandering line in **Figure 5** is used to replace the main resonant line in PIFA shown by combination of horizontal and vertical lines to form multiple turns.

The requirements of the PIFA are the operation frequency, power transmission efficiency, size and even cost. Simulation, fabrication and measurement are conducted until the antenna fulfills the defined application requirements. In general, a well-designed PIFA has the feature of having resonance at the operation frequency and good return loss, i.e., effective power transmission to antenna and compact in size.

**Figure 4.** *Typical PIFA structure [13].*

**Figure 5.** *PIFA with meandering line.*

High directivity sometimes is considered in certain situation. However, it will not be discussed here since most of planar antennas are omni-directional transmission and reception instead of unidirectional antennas. The basic design rules and antenna performance characterization methods are addressed by case study in 2.4 GHz ISM band. The operation frequency of the antenna is governed by the basic dispersion relation *c = fλ*. The letter *c* represents the speed of electromagnetic wave in the air, which is a constant if only consider the wave traveling in single medium. In previous section, it shows that a dipole antenna resonates when the physical length of antenna equals to the quarter wavelength of incident signal and a sufficiently large ground plane form the mirror image under the plane. The length of the resonant line occupies a considerable area on the PCB, which is around one third of a wireless module. Proper selection of traces' length and width reduces the occupied area and impedance matching network for maximum power transfer [13].
