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.