Linear-to-Circular Polarization Converter With Wide Angular Stability and Near Unity Ellipticity—Application to Linearly Polarized Antenna Array
Mohammad Ayoub Sofi, Kushmanda Saurav, Shiban K. Koul
Abstract
A transmission type linear-to-circular polarization converter is proposed using split-rings and metallic strip printed on the both sides of the dielectric substrate and is further utilized to obtain a circularly polarized (CP) antenna array with high gain. The size of the unit cell of the converter is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.394\times 0.374\times 0.15\,\,\lambda _{o}^{3} $ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{o}$ </tex-math></inline-formula> is the free space wavelength with respect to 29.85 GHz). The axial ratio bandwidth (ARBW) and ellipticity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${e}$ </tex-math></inline-formula> ) of the polarization converter remain relatively stable under both the transverse electric (TE) and transverse magnetic (TM) polarization up to oblique incidence of 60° and 45°, respectively. The proposed converter exhibits a measured ARBW of 9.67% (29.50–32.50 GHz). Furthermore, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${e}$ </tex-math></inline-formula> lies in the range of 0.94–0.98 in the operating band of the converter. The CP antenna array with an overall size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.38\times 4.38\times 0.75\,\,\lambda _{o}^{3} $ </tex-math></inline-formula> is obtained by placing a 45° rotated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15\times15$ </tex-math></inline-formula> array of converter’s cells broadside to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times4$ </tex-math></inline-formula> linearly polarized (LP) patch antenna array and exhibits measured peak gain of 18.7 dBic. The proposed polarization converter and CP antenna array can find applications in the uplink Ka-band fixed-satellite services (29.5–30.0 GHz).