Optimisation of a PIFA Antenna Using Genetic Algorithms Pedro Pinho, J. F. Rocha Pereira Instituto de Telecomunicações - Universidade de Aveiro, 3810 Aveiro, Portugal Abstract This work presents the optimisation of PIFA (Planar Inverted-F Antenna) antennas in order to achieve a large bandwidth in the 2 GHz band, using an optimisation technique based on genetic algorithms. During the optimisation process, the different antenna models have been evaluated using the finite-difference time domain (FDTD) method. As a result of this optimisation, a simple PIFA antenna was obtained with a bandwidth of 460MHz and an even greater bandwidth of 570MHz was achieved with a double PIFA antenna with the same overall dimensions. I. INTRODUCTION The increase in the capacity and quality of the new services provided by mobile communications requires the development of new antennas with wider bandwidths. At the same time, due to the miniaturisation of the transceivers, the antennas should have small dimensions, low profile and the possibility to be embedded in the terminals. In this context, PIFA antennas are able to respond to such demands [1]. Its conventional geometry, i.e., the simple PIFA is shown in Figure 1a and an alternative geometry, the double PIFA, is shown in Figure 1b. y x z x y z h Ground Plane Wire h1 Ground Plane h Wire (a) (b) s l w f x f y (c) Fig. 1 Geometry of the PIFA antennas (a) Simple PIFA (b) Double PIFA (c) Top view As seen in Figure1, PIFA antennas have several parameters such as the heights h and h 1 of the radiating plates, the feed position f x and f y , the radius r o of the feeding wire, the width s of the short circuit plate, etc.. All these parameters play a key role in the performance of the antennas, as has been shown by the authors in previous works [2], [3], and as it shown, for a particular case, in Figure 2. 1,0 1,5 2,0 2,5 3,0 1,8 1,9 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 Frequency (GHz) VSWR fx=6 fy=0 h=10 fx=4 fy=2 h=8 fx=4 fy=4 h=8 (in mm) Fig. 2 Influence of the feed position in the input impedance In order to achieve optimal performance from these antennas for a particular application, the geometry of the antenna must be optimised. The search for the best geometry requires an optimisation tool, and one promising tool for this purpose is based upon genetic algorithms. These algorithms are global numerical-optimisation methods, patterned after the natural process of genetic recombination and evolution, [4]. This work follows a sequence of previous work done by the authors and it describes the optimisation of two PIFA antennas to achieve the largest bandwidth in the 2 GHz band, using an optimisation technique based on genetic algorithms. During the optimisation process, the different antenna models were evaluated to determine their performance. The finite- difference time domain (FDTD) method was used to carry out this evaluation [5], [6]. II.METHOD OF ANALYSIS AND EVALUATION The authors have already used the FDTD method for the simulation of PIFA antennas in previous works [2], [3]. The derivation, as well as the practical implementation of this algorithm, are well covered in literature [5], [6] and therefore will not be covered in this paper. The general features of the present algorithm are as follows: the spatial region where the fields are computed was divided by a three dimensional rectangular grid with cell size ∆x, ∆y, ∆z in the x, y, and z directions, respectively. For the results that follows, cell sizes were ∆x=∆y=∆z=2mm, with the time increment at the Courant limit. The outer boundaries of the FDTD computational space were terminated by second-order Mur numerical absorbing boundaries to reduce the reflection of scattered fields. The absorbing boundaries were at 20 cells away from the antenna in all directions. The structure modelled for this work consists of rectangular