Compressed Dipoles Resonating at Higher Order Modes With Enhanced Directivity

A compressed dipole operating at higher order modes is proposed and investigated for the enhancement of boresight directivity. Compared with conventional dipoles in free space, the length of the proposed dipole is compressed although the currents on the compressed dipole still sinusoidally distribute. The traces of calculated compressed dipole's directivity against compressibility show that the directivity of a compressed dipole operating at higher resonant modes is larger than conventional dipoles for the well selected compressibility. This paper shows that printing the dipole onto a piece of dielectric substrate can achieve the desired compressibility. The relationship between the compressibility and relative permittivity of the dielectric slab provides the guidance to realize the selected compressibility. As an example, a thin linear compressed dipole resonating at the third mode is designed, fabricated, and measured to validate the method. The measured broadside gain of the proposed compressed dipole reaches up to 4.6 dBi, 75% or 2.45 dBi higher than a conventional dipole.