Ultra-broadband omnidirectional printed dipole arrays

The paper presents a novel antenna concept based on combining the logarithmic-periodic antenna with the loop antenna. This concept allows realization of very broadband antennas with unique radiation properties -omnidirectional radiation pattern and horizontal polarization. The antenna concept is derived from a small loop antenna by replacing the wire of the loop by small dipoles arranged on a circumference and fed in phase along the circumference. This small dipole structure is then extended to antenna structures with half-wavelength dipoles incorporating different feeding techniques. The logarithmic-periodic principle is then applied to attain ultra-broadband radiation properties. The obtained antenna designs can be used alone or in combination with a vertically polarized antenna as a multi-band indoor base station antenna with horizontally polarized or dual-polarized omnidirectional radiation patterns.