Compound Metaloop Antenna for Circularly Polarized Beam Steering

A metaloop antenna (1FD-MetaLPA), made of C-type metaatoms and having a single feed point, F
_L
', is created to radiate a left-hand circularly polarized (LHCP) axial beam at a frequency of f
_LH-1FD
= 2.55 GHz and a right-hand circularly polarized (RHCP) axial beam at a frequency of f
_RH-1FD
= 3.45 GHz. It is revealed that the maximum gains at f
_LH-1FD
and f
_RH-1FD
are unbalanced. Subsequently, a number of C-type metaatoms are replaced by N-type metaatoms. The replacement generates a balanced gain of 7.1 dBi with an LHCP gain bandwidth of 7.7% and an RHCP gain bandwidth of 8.3%. The radiation efficiency under the balanced gain is 75% at f
_LH-1FD
and 29% at f
_RH-1FD
. Next, a large metaloop antenna that radiates a conical beam and has a feed point, F
_O
, is concentrically added to the outside of the gain-balanced 1FD-MetaLPA. This antenna system is designated as the MetaLPA-plus. It is found that the MetaLPA-plus radiates an LHCP tilted beam at f
_LH-1FD
and an RHCP tilted beam at f
_RH-1FD
. The angle of depression (tilt angle) using equal amplitude excitation is θ
_max
= 20
^°
at f
_LH-1FD
and θ
_max
= 15
^°
at f
_RH-1FD
. These tilted CP radiation beams are rotated around the antenna axis with change in the excitation phases at points F
_L
' and F
_O
. During the beam-steering, the gain for an LHCP wave is nearly constant, with a value between 5 dBi and 6.5 dBi. This also holds true for an RHCP wave.