A feed network for the selective excitation of specific characteristic modes on small terminals

We investigate different strategies to realize a feed network for a set of ICEs (Inductive Coupling Elements) on a small terminal for the selective excitation of characteristic modes. The inductive excitation is realized by embedding small rectangular loops into the PCB (Printed Circuit Board) of the terminal. Due to the small dimensions of the ICEs the input impedance of the elements is highly reactive. Therefore, additional matching networks are required. The trade-offs of lumped elements versus distributed transmission lines to match and combine the elements of each set of couplers are investigated. An important result obtained is that the feed network with double-stub tuning offers advantages compared to the feed network with lumped SMD (Surface Mountable Device) components with respect to the efficiency of the entire antenna systems.