Low profile and wideband planar inverted-F antenna with polarisation and pattern diversities

A low profile (height = 3 mm) and wideband dual coplanar feed planar inverted-F antenna (PIFA) is proposed for diversity applications over the frequency range of 2.35-3.25 GHz with a fractional bandwidth of 32%. It covers LTE bands 7, 38, 40, 41 and WiFi frequency bands. The design is based on a comparative study on the mutual coupling between different feed arrangements such as the parallel feed, coplanar feed and orthogonal feed. The results show that the coplanar feed arrangement exhibits a lower mutual coupling level. As a result, the coplanar feed is employed in the proposed antenna and the polarisation diversity is achieved by exciting two orthogonal radiation modes; the antenna fed by Feed 1 uses open ground plane slot in the horizontal plane, while the antenna fed by Feed 2 is linked to PIFA. The modified top plate provides a self-matching circuit for Feed 2. The isolation between the feeds is achieved by an L-shaped ground plane slot. Both simulated and measured results are obtained, and the results demonstrate that the proposed antenna is a very good candidate for mobile diversity and multiple-input and multiple-output applications.