A U-Shaped Low-Profile Metaline Array Antenna for a Circularly Polarized Fan-Beam Across Two Frequency Bands

A novel low-profile array antenna composed of two U-shaped metalines I and II is realized for a circularly polarized (CP) fan-beam. First, the radiation from metaline I is investigated. The investigation reveals that the metaline generates a right-hand (RH) CP broadside beam at two design frequencies of f(low) = 2.6 GHz and f(high) = 3.6 GHz. The half-power beamwidths (HPBWs) in the E- and H-planes are almost the same: approximately 100 degrees at f(low) and 90 degrees at f(high). Next, the two metalines I and II are simultaneously excited in equal-amplitude with out-of-phase. The HPBW in the E-plane becomes narrower than that in the H-plane: 44 degrees in the E-plane and 102 degrees in the H-plane at f(low), whereas 45 degrees in the E-plane and 96 degrees in the H-plane at f(high). That is, a CP fan-beam is formed. The 3 dB axial ratio bandwidths are approximately 10.4% and 9.6% around f(low) and f(high), respectively. Across these bandwidths, the reflection coefficients (S11 and S22) are less than -10 dB and the mutual coupling (S21) is less than -15 dB. The fabricated antenna confirms the validity of the simulated results.