Further investigation of a dual-element diversity PIFA for MIMO applications at 2.5 GHz band

Multiple input multiple output (MIMO) technology has been regarded as a practical approach to achieve significant increases of wireless channel capacity or reliability. Recently, the antenna´s effect on MIMO system has been investigated intensively, in order to predict the true spectral efficiencies of MIMO systems in a real environment whereby realistic mobile terminals are used. Separation between multiple antenna elements is the most critical parameter affecting mutual coupling. Analytical studies have shown that for minimal or no mutual coupling, the distance between typical antenna elements needs to be at least half wavelength. However, the large separation between antenna elements is not attainable on a mobile terminal. There are a number of suggestions on how to build diversity antennas on a mobile terminal with low mutual coupling. In this context, we have developed a modified planar invert-F antenna (PIFA) and built a dual element array operating in 5.2GHz band with a separation of less than half wavelength (0.35 wavelength) and an isolation better than 28dB, as presented in our previous studies. It is noticed that mutual coupling depends on the frequency of received/transmitted signals since the distance is expressed in terms of the wavelength. Therefore, a dual-element diversity PIFA operating at the lower frequency (2.5GHz band) with an even closer separation (0.17 wavelength) has been studied in this paper.