“…Regarding the feeding networks, we can distinguish between those that use switches [10,13], phase shifters [11,12,20,31], phase shifters with switches [17,21,29], vector modulators (reconfigurable amplitude and phase) [18,19,[22][23][24][25][26]30,32], IQ data separately encoded transmitters [14,27], retrodirective array [28] and a Fourier Rotman lens [15,16]. Some of the reported architectures [14][15][16]27,28] do not require a synthesis method for the antenna weights since the feeding network generates DM straightforwardly. Among the reported synthesis methods, we can find some that make use of brute force and explore all the possible combinations allowed by the architecture by searching for those that generate the desired constellation in the secure direction [10,13,20].…”