Emitting phased array RF systems have to contend with an ever-increasing number of eavesdroppers as technological advancements provide lower cost and/or more capable radios. Often, eavesdroppers can accumulate sufficient information transmitted in sidelobes by integrating over long enough periods. Directional modulation (DM) disrupts this capability by inducing a randomized walk through IQ-space to reach a pertinent location which corresponds to a symbol of particular amplitude and phase. This results in higher secrecy capacity. The path taken by the cumulative element contributions are determined by the complex weights of individual transmitters. Because large phased arrays support a large number of available paths, repetitions of applied weights are not concerning. The same cannot be said for arrays that consist of only a few elements, e.g. WiFi routers. We introduce a computationally efficient and flexible framework for DM that utilizes real-valued phase rotations of element weights. It supports a wide family of modulation schemes in phase and/or amplitude. Using state-of-the-practice orthogonal noise injection framework, we demonstrate a richness of unique paths resolving concerns about repeated weights. In our proposed scheme, there is a small reduction in received power compared to traditional beamforming, as little as 1 dB, which is an advantage over conventional directional modulation which typically sacrifices 6 dB of power. Also, there is a significantly larger set of possible element weights than that of the conventional scheme. This feature protects against the possibility of eavesdroppers breaking the distortion-based obfuscation of symbols over repeated observations. Our approach provides more secrecy capacity than conventional directional modulation via increased power delivery and increased receiver SNR and does so with resilience to advanced eavesdropping threats.

8 pages, 11 figures. Full version of paper submitted to 2024 IEEE Phased Array Conference