A novel miniaturized triband PIFA for MIMO applications

Multiband antennas are vital in meeting the modern tele- communication demands of mobile terminals. Using the spatial properties of multipath channels, multiple-input multiple-output (MIMO) communica- tion systems employ antenna arrays to increase their communication capac- ity. This article presents a novel printed inverted "F" antenna (PIFA), which has been used to design a miniaturized triband antenna. In turn, the triband antenna has been used as an element in various arrays of MIMO applications. Specifically, the antenna element has been constructed and applied, in arrays of two and four, in a laptop PCMCIA wireless LAN card. The size of the four element MIMO antenna array is 50 mm 13 mm 8 mm, which translates to 0.4 0.1 0.06 at 2.45 GHz. The input im- pedance of the single element antenna has been measured at UCLA. The antenna has a return loss lower than 10 dB within the 2.4 -2.5 GHz, 5.15-5.35 GHz, and 5.7-5.85 GHz bands. The measured scattering matri- ces of two and four element arrays have been used to calculate the total active reflection coefficient (TARC). TARC has been calculated for different combinations of excitation signals applied at each port. Each excitation signal has a unity magnitude and a random phase, thus leading to innumer- able signal combinations. Our results reveal that "off" diagonal elements of the scattering matrix (couplings between elements) are as important as di- agonal elements in calculating the TARC and the radiation efficiency of arrays. Furthermore, increasing the number of elements in a MIMO system with a limited volume will increase the channel capacity but lower the radiation efficiency. The experimental and simulation results have been in agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 724 -731, 2007; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.22239

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