Investigation on the reactance loading and EM coupling feed for a design of a dual frequency planar antenna

We investigate the design method for a compact antenna composed of an exciting loop and parasitic loops which are electromagnetically coupled for a dual frequency operation. First, we presented a useful formula for determining the reactance load which makes the parasitic loop to be resonant or nearly resonant. Electromagnetic coupling mechanism were analyzed by using impedance matrix between antenna elements and design formulas for adjusting impedance matrix elements were also presented. Based on the presented formulas, the prototype planar antenna printed on a FR-4 PCB was fabricated and the comparison between calculated and measured results ensured the validity of the design method.