Compound Metaloop Antenna for Circularly Polarized Beam Steering

A metaloop antenna (1FD-MetaLPA), made of $C$ -type metaatoms and having a single feed point, $F_{\mathrm {L}}$ ’, is created to radiate a left-hand circularly polarized (LHCP) axial beam at a frequency of $f_{\mathrm {LH-1FD}} =2.55$ GHz and a right-hand circularly polarized (RHCP) axial beam at a frequency of $f_{\mathrm {RH-1FD}} =3.45$ GHz. It is revealed that the maximum gains at $f_{\mathrm {LH-1FD}}$ and $f_{\mathrm {RH-1FD}}$ 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 $f_{\mathrm {LH-1FD}}$ and 29% at $f_{\mathrm {RH-1FD}}$ . Next, a large metaloop antenna that radiates a conical beam and has a feed point, $F_{\mathrm {O}}$ , 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 $f_{\mathrm {LH-1FD}}$ and an RHCP tilted beam at $f_{\mathrm {RH-1FD}}$ . The angle of depression (tilt angle) using equal amplitude excitation is $\theta _{\mathrm {max}} = 20^{\circ }$ at $f_{\mathrm {LH-1FD}}$ and $\theta _{\mathrm {max}} = 15^{\circ }$ at $f_{\mathrm {RH-1FD}}$ . These tilted CP radiation beams are rotated around the antenna axis with change in the excitation phases at points $F_{\mathrm {L}}$ ’ and $F_{\mathrm {O}}$ . 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.