Investigations into Operation of Single- and Multi-Layer Configurations of Planar Inverted-F Antenna

The paper presents a tradeoff analysis between single- and multi-layer (stacked) configurations of a planar inverted-F antenna (PFIA) of fixed overall height, with respect to achieving multi-band operation. The investigations focus on two bands, 800 to 1000 MHz and 1700 to 2600 MHz, which cover a frequency spectrum allocated to most of the present-day wireless systems operating below 2600 MHz. Folding and tapering of a conducting patch in the single-layer configuration, and increasing the number of conducting patches in the multi-layer layer (stacked) configuration, are used to achieve multi-band operation. The results obtained show that the stacked PIFA is able to generate many (four or more) bands within the investigated frequency spectrum. However, it faces difficulty in broadening them, as the coupling of upper plates to the ground is weakened by the presence of middle plates. At the same time, the tuning of one band adversely affects the other bands´ performance. For the single-layer PIFA, the multi-band impedance characteristics are easier to adjust. A significant band widening can be obtained by proper arrangement of a conducting patch, and by introducing cuts or slits in the ground plane. In the designs presented, the antenna volume, measured by its outline, fell under 3 cm³. The resulting radiation efficiencies were 95% at the lower band (900 MHz), and 89% at the upper frequency range (2020 MHz).