Dual-Band, Orthogonally-Polarized LP-to-CP Converter for SatCom Applications

A systematic design of dual-band, orthogonally-polarized linear-to-circular polarization (LP-to-CP) converters is proposed. This class of polarization converters can transform linearly polarized waves into right- and left-hand circularly polarized (RHCP and LHCP) waves in two separate non-adjacent frequency bands. The reported polarizer is made of three cascaded bianisotropic sheet admittances, spaced by two isotropic dielectric slabs. The electromagnetic problem is studied using impedance boundary conditions. A transmission-matrix analysis of periodically-loaded transmission lines is employed in the design. An analytic model is developed, and closed-form expressions are derived for the frequency response of each sheet admittance. This method avoids the use of multi-parameter optimization procedures. An example of a dual-band, orthogonally-polarized LP-to-CP converter is proposed for satellite communication applications in the K-/Ka -band. The polarizer separately performs LP-to-LHCP and LP-to-RHCP conversions over the transmit (TX) and receive (RX) channels of the K-/Ka -band. The design is validated with a prototype. Under normal incidence, the polarizer exhibits axial ratio (AR) lower than 3 dB over the 18–22.2 (~21%) and 28.7–30.4 GHz (~6%) bands. The total transmission is above −1 dB within the same two bands. The performance is stable for scanning angles up to ±45°. For a 45° angle of incidence, the AR is lower than 3 dB in the bands 17–22 (~25.6%) and 28.6–30 GHz (~4.7%) with a total transmission higher than −1.2 dB.