Figure 1

Scattering parameters of an example compact branch-line coupler (consider in “Example 1: Miniaturized branch-line coupler (BLC)”). The target operating frequency is 1.8 GHz, marked using a vertical line. This target is attainable by means of local search when starting from the design represented using the black lines; however, it is not attainable from the design marked using the gray lines. The latter is due to the fact that the operating bandwidth of the circuit is too far away from the target frequency.