Dual-Band, Wide-AR Beamwidth, CP Antenna With Artificial Reflecting Surface for Hypersonic Vehicles

In integrated communications and navigation systems on hypersonic vehicles, circularly polarized (CP) antennas require wide axial-ratio (AR) beamwidths to ensure the reception of signals at low elevation angles, even when embedded in a thermal protection system (TPS). This paper analyzes electromagnetic interactions between CP antennas and TPS through the reciprocal and transmission line (TL) theories. A method is proposed to design an artificial reflecting surface (ARS) by calculating its optimal equivalent circuit. The designed ARS restores the CP properties of an embedded antenna by substituting its perfect electric conductor (PEC) ground. A dual-band 3/7 GHz CP antenna is designed and fabricated to verify the proposed theoretical method. By loading a double-layer ARS with serpentine loop and serpentine slot units, several negative effects of TPS are mitigated, resulting in resonance depth restoration and AR bandwidth widening. In particular, the 3 dB AR beamwidth of the proposed CP antenna covered by a double-layer TPS is significantly broadened, whose AR beams are widened to 110° on average in the frequency range of 2.91-3.16 GHz and to 65° on average in the frequency range of 6.69-7.22 GHz. The realized CP gains of the antenna are more than 5.0 dBc throughout the working bands.