Physical layer security incorporates security features embedded in the communication channels without the need to exchange cryptographic keys. Interest in exploiting such mechanisms has been increasing rapidly for 5G and beyond, due to the low overhead and low-latency properties of such encoding. Although phased arrays, by their nature of the focused beams to users, introduce secrecy, they are still vulnerable to eavesdropping at the sidelobes. In this article, we present a class of spatio-temporal modulated arrays (STMAs) with custom CMOS integrated circuits (ICs) and packaged antennas operating in the 71–76-GHz range that creates secure cones in space by preserving signal fidelity in the intended direction while emulating a time-varying channel outside the secure cone. At unintended directions, the architecture intentionally spectrally aliases signals to create noise-like features and scrambles constellations with a one-to-many mapping (including infinite constellation splitting), making it challenging to invert the mapping by eavesdroppers. Through the architecture, the secure cone can be reconfigured in space on demand and narrowed when we increase the number of elements. We also show how reconfigurable time modulation (such as through frequency chirping) can create a non-repetitive mapping of the constellation to protect against colluding attacks.