A Compact Dynamic Antenna for Physical-Layer Wireless Security

Wepropose a novel omnidirectional antenna design incorporating directional modulation at the antenna pattern level for secure narrow planar information transmission. The proposed antenna features a compact size and stable omnidirectional radiation performance by employing two tightly spaced, printed meander line monopole antennas, acting as a single radiating element. To achieve a narrow secure information region, the antenna is fed by differential power excitation at the two ports with real-time electronically controlled dynamic switching. This leads to phase pattern modulation only along the electrical polarization, resulting in a directionally confined region where information is recoverable in the E-plane, while maintaining a highly constant or static omnidirectional H-plane pattern, inducing a 360$^\circ$information recoverable region. The dynamic antenna is designed and fabricated on a single layer of Rogers RO4350B which provides a miniaturized planar size of 0.36×0.5$\lambda _{0}$$^{2}$at 2.7GHz. The fabricated antenna is directly fed with a 10dB power ratio by a radio frequency (RF) switching system and evaluated for 16-QAM and 256-QAM transmission in a high signal-to-noise ratio (SNR) environment. For 16-QAM transmission, a narrow E-plane information beam (IB) of approximately 34$^\circ$and omnidirectional H-plane IB are obtained, and a narrower E-plane IB is achieved around 15$^\circ$for 256-QAM.