A high directivity, compact, omnidirectional horizontally polarized (OHP) antenna array is developed for wirelessly powering internet-of-things (IoT) devices. The antenna array is realized by seamlessly inserting several phase inverters inside an electrically long TE0.5,0 mode open waveguide. The phase inverter consists of a meandered slot and eight shorting vias. The meandered slot creates an interdigitated structure on the top surface of the waveguide; it introduces capacitance. The eight shorting vias are placed in an alternating pattern on the two sides of the slot; they produce inductance. The combination of the slot and vias forms a bandpass effect and inverts the electric fields in the waveguide. Consequently, a collinear and in-phase magnetic dipole array is realized. A compact eight-element OHP magnetic dipole array is designed, fabricated and measured. The measured results confirm the design concept and high directivity (10.4 dBi), omnidirectional HP radiation pattern has been achieved.