Design and Evaluation of a PIFA Array for MIMO-Enabled Portable Wireless Communication Devices Rashid A. Bhatti*, Mingoo Choi, JangHwan Choi, and Seong Ook Park Information and Communications University, Yuseong-gu, Daejeon, Korea E-mail: {rashid, layers, jhchoi, sopark}@icu.ac.kr Introduction Performance of MIMO-enabled portable devices is heavily dependent on the characteristics of its antenna arrays [1]-[2]. A typical MIMO antenna array for portable devices should have compact structure, high radiation efficiency, and low spatial correlation in addition to the required bandwidth and nearly omni-directional radiation pattern. Various MIMO antenna arrays for portable devices have been reported in the literature where mostly the frequency of interest is either 2.4 GHz or 5.2 GHz [3]-[8]. In this paper, design and experimental characterization of a four-element PIFA array for MIMO-enabled portable devices is presented. Basic element of the array is a compact PIFA structure with a volume of 0.16 cm 3 . PIFA elements are symmetrically located at the corners of a rectangular PAD-sized ground plane. The antenna array is initially characterized by measuring scattering parameters and radiation patterns at the individual antenna ports. In order to measure channel impulse responses, indoor MIMO measurements under line-of-sight (LOS) and non-line-of-sight (NLOS) propagation conditions are then performed for a linear array of monopoles and the PIFA array. The measured channel data is then post-processed to evaluate spatial correlation and capacity for the two arrays. Power azimuth spectrum (PAS) at LOS and NLOS locations is estimated to determine the angle-of-arrival information for the significant multipaths. Capacity and spatial correlation for the PIFA array under both propagation scenarios are compared to that of the standard quarter-wave monopole array. Design of PIFA Array The proposed MIMO array consists of four elements symmetrically located at the corners of a PDA-sized ground plane. Basic element of the array is a single band PIFA with L- shaped slot in the horizontal part of the radiating element. Slot is created to increase the surface current path length. The PIFA structure is bent at the slot for further compact construction resulting in a total volume of 0.16 cm 3 . The antenna has a 1 mm wide short- circuiting strip and is fed through a semi-ridged coaxial cable. PIFA element and the array are shown in Figure 1(a) and (b) respectively. Spacing between the feed and short points is adjusted for impedance matching over the desired frequency band of 3.7 GHz to 4.2 GHz. Dependence of the antenna operating frequency on slot length is shown in Fig. 2(a). S-parameters of the array are shown in Fig. 2(b). The antennas were fabricated using a copper sheet of 0.2 mm thickness. The PIFA array was then characterized initially by measuring scattering parameters and radiation patterns and finally through indoor MIMO measurements. Radiation patterns of PIFA-1 in the array environment are shown in Fig. 3. A four-element linear array of quarter-wave monopoles was also constructed and used to measure the channel matrix for comparison purposes. Spatial correlation and capacity are calculated through the measured channel matrix data for both the proposed PIFA and the monopole arrays. 978-1-4244-2042-1/08/$25.00 ©2008 IEEE