Theoretical Investigation of Radiation in the Normal Direction for a Metaloop Antenna

Radiation in the normal direction for a metaloop antenna is discussed. First, the radiation field generated from an N-type current distributed along a loop, E
_N
, is investigated. The investigation clarifies the behavior of the unbalance between the left-handed circularly polarized (LHCP) component of E
_N
at frequency f
_(-)
and the right-handed circularly polarized (RHCP) component of EN at frequency f
₍₊₎
, where the loop circumference at these frequencies is one guided wavelength. Secondly, the radiation field generated from a C-type current, E
_C
, is investigated. The second investigation, when combined with the first investigation, leads to an inference that balanced radiation (and hence balanced gain) will be obtained when the N-type current over a certain region of the loop is replaced with a C-type current. Thirdly, to check this inference, a radiation field generated from a composite of the N-type and C-type currents, E
_NC
, is formulated. Using this formulation, the ratio of the gain for an LHCP wave to the gain for an RHCP wave, G
_r
, is derived. Fourthly, a metaloop antenna simulation model that has a balanced gain is created using practical N-type and C-type metaatoms that realize the composite current. Finally, a metaloop antenna is fabricated on the basis of the antenna simulation model. Measurements confirm that the fabricated metaloop antenna has a balanced gain in the normal direction. As supplementary data, the radiation pattern and VSWR of the fabricated metaloop antenna are also presented, together with the radiation efficiency and some comments.