Finite-difference time-domain analysis of a stacked dual-frequency microstrip planar inverted-F antenna for mobile telephone handsets

We describe a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work in two frequency-bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz, respectively. The proposed microstrip DF-PIFA is fed by a coaxial line, as opposed to two separated feed lines used in the conventional design. The design is carried out in a systematic manner and involves two steps. We begin with an initial configuration of the PIFA that is based on a standard design for a microstrip patch antenna fed by a coaxial line and is derived from an empirical approximation in conjunction with a transmission line model. Next, we employ a computer-aided design (CAD) tool, based on the nonuniform finite-difference time-domain (NU-FDTD) Maxwell solver, to optimize the performance characteristics of the DF-PIFA, including the return loss, the matching of the input impedance, and the far-field radiation patterns.

I. Introduction

IN recent years, there has been an explosive growth in the market demand for cellular communication systems. In many parts of the world, two operating systems are being simultaneously used for mobile communication, viz., the GSM and DCS 1800 systems, operating at 0.9 GHz and 1.8 GHz, respectively. Thus, it is highly desirable to design a built-in antenna for cellular telephone handsets so that it operates at two discrete frequency bands, and yet concurrently meets the stringent requirements on both the electrical performance and the physical dimensions of the allocated space for the antenna. Various types of the planar inverted-F antennas (PIFAs) have been proposed for this application, because they are compact in their dimensions, are easy to manufacture, and exhibit good electrical performance [1]–[5]. The primary design tool, employed in the previous works, is the finite-difference time-domain (FDTD) method, owing to its capability, flexi-bility, and accuracy in modeling a complex geometry [6].