Frequency-Selective Surface-Based Compact Single Substrate Layer Dual-Band Transmission-Type Linear-to-Circular Polarization Converter

In this article, a compact dual-band linear-tocircular polarization converter designed on a single-layer substrate is proposed. The unit cell of the converter has a size of 3.72 × 3.90 × 1.52 mm
³
(0.0072λ
₀
³
, λo is calculated with respect to 20.67 GHz). The converter consists of split rings and a pair of metallic strips printed on both sides of a single-layer substrate for dual-band operation. The proposed converter has a measured 3-dB axial ratio bandwidth of 5.56% (20.10-21.25 GHz) in the lower band and 3.97% (29.12-30.30 GHz) at the upper band. The converter transmits a right-hand circularly polarized (RHCP) wave at the lower band and left-hand circularly polarized (LHCP) wave at the upper band for a linearly polarized (LP) incident wave. The characteristics of the polarization converter are validated by integrating an array of 7 × 7 elements of its unit cell in the endfire direction of a dual-band LP dipole antenna operating in the same frequency bands such as that of the polarization converter. The antenna integrated with the polarization converter exhibits measured circularly polarized (CP) bandwidths of 7.80% and 6.57% in the lower frequency band: 20.10-21.75 GHz and the upper frequency band: 29.4-31.4 GHz, respectively. The integrated antenna can act as a feed source of a high-gain dualband transmit array for uplink (30.0-31.0 GHz) and downlink (20.2-21.2 GHz) of Ka-band military satellite communication.