Low-Profile, Pattern-Reconfigurable, Electrically Small Antenna Based on Equivalent Even and Odd Modes

A pattern-reconfigurable electrically small antenna (ESA) that radiates circularly polarized broadside pattern and linearly polarized omnidirectional pattern is proposed. The ESA consists of four dipole arms on the top layer and five dipole arms on the bottom layer. The two layers are connected by five vertical shorting pins. The connection states between different dipole arms and pins are electrically controlled by three inserted PIN diodes to generate the equivalent even- and odd-mode states, which correspond to reconfigurable broadside and omnidirectional patterns. The measured results demonstrate that in the odd-mode state, the boresight realized gain (RG) and axial ratio, front-to-back ratio, and radiation efficiency (RE) are 3.22 dBic, 2.57 dB, 6.39 dB, and 65.2%. In the even-mode state, the measured RG, out-of-roundness values, and RE of the omnidirectional pattern are 1.55 dBi, 2.19 dB, and 92.2%. Corresponding to the wavelength of 1.616 GHz, the profile is 0.04
λ
₀
, and the cross-section is π × 0.15
²
λ
₀
²
, i.e.,
ka
= 0.98.