Multi-band planar inverted-F antenna with microstripline coupling to open-end ground slots

In this paper, a new excitation technique for a printed planar inverted F antenna (PIFA) is described to obtain multi-band operation. In the proposed technique, the printed PIFA is fed from a microstrip line which is coupled to open-end slots in a finite ground. A strong coupling between the microstripline and the ground slots is responsible for generating new resonant frequencies in addition to the one generated by the PIFA element. In contrast to the traditional coaxial probe feed, the use of the microstrip feed allows for coupling to arbitrarily located and orientated ground slots. The advantage of the proposed technique is demonstrated in design examples of multi-band PIFA operating within the 2.4 to 6 GHz frequency band. In the proposed design strategy, the PIFA element of quarter wave length is designed for operation at 2.45 GHz while the location and dimensions of open-ended ground slots are selected to obtain operation at higher frequencies. Two configurations of open-end slots in the ground plane are demonstrated. In the first configuration, an open-end ground slot is chosen to be parallel while in the second configuration the ground slot is selected to be perpendicular with respect to the PIFA element. The multi-band PIFA performance is assessed in terms of return loss, radiation pattern and distribution of surface currents around the primary radiating element and the ground slots at resonant frequencies. The antennas have been fabricated and the experimental results are in good agreement with the simulation.