A Compact Cross-Structured Dynamic Antenna for Reconfigurable Directional Modulation

A compact cross-structured dynamic antenna is presented for antenna-level physical-layer security using reconfigurable information-beam control rather than conventional radiation beam steering. The antenna uses four printed meander-line monopoles in a planar cross structure and a switching network that realizes two complementary excitation states for each dynamic mode. By switching between opposite or diagonal port groups, the aperture introduces apparent two-dimensional phase center displacement and supports four information-beam directions: $\varphi=0^\circ$, $45^\circ$, $90^\circ$, and $135^\circ$. An average--differential array factor formulation shows that the average component preserves broad omnidirectional coverage, while the odd-symmetric differential component creates angle-dependent magnitude and phase distortion that determines where the constellation remains recoverable. The recoverable information region is therefore reconfigured without phased-array beamforming, multiple RF chains, or mechanical motion. A 5.05-GHz prototype on Rogers RO4350B is fabricated with an electrical footprint of $0.57 \times 0.47λ_0^2$. Measured 16-QAM results show that low bit error rate is confined to the intended E-plane information-beam sectors, while off-beam angles exhibit large magnitude and phase errors, elevated BER, or unrecoverable constellations despite high received SNR. The measured H-plane cuts maintain low BER over nearly the full angular range, confirming omnidirectional information recovery in the orthogonal plane.

A Miniaturized Dynamic Array for Antenna-Level Physical Layer Security

A compact dynamic omnidirectional array is proposed for antenna-level physical-layer security through directional modulation. Unlike conventional directional-modulation transmitters based on phased-array beam synthesis or multiple RF chains, the proposed architecture uses a single RF input and a switching-controlled four-element printed meander-line monopole array operating at 5.05 GHz. The state-dependent excitation introduces controllable magnitude and phase perturbations in the radiated field, producing angle-dependent constellation distortion and bit error rate behavior. Reliable information recovery is confined to a narrow broadside region in the E-plane, whereas the H-plane remains quasi-static and omnidirectional, providing a full 360-degree information-recoverable region. The antenna is implemented on a single-layer Rogers RO4350B substrate with a compact footprint of 0.57 x 1.11 lambda_0^2. A four-path switching network based on commercial RF components is used for experimental validation. Communication measurements using 16-QAM at 5.05 GHz demonstrate BER-defined E-plane information beamwidths of 30 to 36 degrees for calibrated switching modes under a BER <= 10^-3 criterion, while no bit errors are observed in the measured H-plane and the SNR remains above approximately 33 dB. Feed-phase offsets are also used to steer the BER-defined information-recoverable sector, demonstrating information-beam steering with the same antenna-level switching mechanism. These results show that compact antenna-level directional modulation can provide angularly selective information recovery in one principal plane while preserving omnidirectional coverage in the orthogonal plane.

A Compact Omnidirectional Meanderline Antenna Array for Wireless Security Using Dynamic Magnitude and Phase Pattern Modulation

A compact dynamic four-element array with omnidirectional H-plane coverage is presented for planar physical-layer security using antenna-level directional modulation. The proposed approach achieves angularly selective information transmission without phased-array beamforming or multiple RF chains by dynamically switching the excitation paths of a four-element array. The antenna comprises four printed meander-line monopole elements operating at 5.05 GHz with independently controlled differential power excitation, which introduces magnitude and phase pattern modulation and dynamic motion of the apparent element spacing, resulting in strongly angle-dependent signal distortion and bit error rate (BER) performance. Reliable information recovery is confined to a narrow broadside region in the E-plane, while significantly elevated BER is observed at off-broadside angles. In contrast, the H-plane radiation remains static and omnidirectional, enabling full 360-degree information-recoverable coverage in the orthogonal plane. The antenna is fabricated on a single-layer Rogers RO4350B substrate with a compact footprint of 0.55 x 1.73 lambda_0^2. A four-path switching network implemented using commercial RF components validates the concept experimentally. Communication measurements under high-SNR conditions above 19 dB using 16-QAM demonstrate a planar information beamwidth below 24 degrees, confirming effective antenna-level directional modulation with angle-dependent BER characteristics and omnidirectional H-plane coverage.

Spatial-Spectral Modeling of the Array Pattern of a Two-Element Dynamic Antenna Array with Differential Amplitude Modulation

We present a theoretical model for a two-element dynamic phased array and characterize the transfer of information as a function of angle. The array is based on a two-state switched structure with phase shifting to support beamsteering. Dynamic motion of the phase center of antenna arrays generates time-varying radiation patterns that, when appropriately designed, support directional modulation, or the transfer of information to regions of space that are narrower than that covered by the energy radiated by the array. We evaluate the impact of switching frequency and steering on the spatial width of the information beam, which is the region of space where information is recoverable. The concepts are evaluated through simulation and experiment using a 0.75$λ$ two-element array operating at 2.5 GHz.

A Compact Dynamic Omnidirectional Antenna

We propose a novel omnidirectional antenna design incorporating directional modulation 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 information secure region, the proposed antenna is fed by differential power excitation of two ports with real-time dynamic switching. This leads to phase pattern modulation only along the electrical polarization, resulting in directionally confined information recoverable region in the E-plane, while maintaining 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 $0.36 \times 0.5 , \lambda_0^2$ at 2.7 GHz and easy integration. To validate the wireless communication performance, the fabricated antenna is directly fed with a 10 dB 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. Experimental results demonstrate that 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. These results confirm that the proposed antenna offers a simple yet effective approach to enhance planar physical information security with a compact dynamic antenna system.