Integration of Planar Antennas Considering Electromagnetic Interactions at Board Level

In compact wireless modules, electromagnetic (EM) interactions occurring between planar antennas and transmission lines (TML) sharing the same substrate may cause a high amount of undesired coupling and may also detune the antenna characteristics. In this paper, an approach for defining a block-out region around the planar antenna, where no components should be placed is developed, thereby ensuring that the antenna characteristics remain within tolerable limits when the antenna is integrated at board level. This region is comparable to the reactive near-field, but is determined by evaluating the reactive EM power density excited on the ground plane and deducing a threshold value. Its boundary will be termed the EM antenna boundary. Furthermore, a method for efficient estimation of EM coupling from the antenna to terminated TMLs routed outside the EM antenna boundary is developed. This method is based entirely on a postprocessing step to field simulations, i.e., the coupling is calculated based on the previously computed magnetic field distribution excited by the antenna on the ground plane. The coupling model uses the theory of field excited TMLs together with the Baum-Liu-Tesche integral equations for obtaining the terminal voltages of the TML and, hence, the coupling terms.