A Compact Ultrawideband Circularly Polarized Antenna Array With Shared Partial Patches

Abstract

In this letter, a compact ultrawideband circularly polarized (CP) antenna array is proposed. The antenna array consists of four cross dipoles with asymmetric elliptical arms and a wideband 1-to-4 feeding network. By employing the ellipses of different sizes as the arms of the cross dipole, the operating bandwidth of the antenna array element can be enhanced. Rotating four of these elements in sequence can obtain an antenna array with symmetrical radiation patterns. The size of the antenna array can be reduced by shortening the distance between adjacent elements and exchanging the upper and lower layers patches of the second and fourth elements to partially overlap between adjacent elements. In addition, the axial ratio (AR) bandwidth can be further expanded because of the sequential rotation topology and the wideband feeding network with a 90° phase difference between adjacent elements. A prototype is fabricated to verify the design principle. The measured and simulation results show that the proposed antenna array has great CP characteristics. The measured impedance bandwidth for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$|S_{11}|$</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">$&lt; $</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB and 3 dB AR bandwidth are about 104.4% and 111.8%, respectively. The peak gain is 13.2 dBic at 4.5 GHz. The overall size of the antenna array is only 0.88 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> × 0.88 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> × 0.14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> refers to the wavelength of the lowest operating frequency in free space).