Miniaturized Ultrawideband Circularly Polarized Antenna With Folded Arms Inspired by the Conventional Vivaldi Antenna

Abstract

A method to reduce the volume of a circularly polarized Vivaldi-inspired antenna array by bending radiation arms is proposed in this paper. Two orthogonal Vivaldi elements form a cross-shaped configuration by rotating sequentially. For miniaturization and impedance match, two arms of the Vivaldi element are bent in opposite directions and then a folded cross-structure antenna is excited by a wideband feeding network with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$90^{\circ }$</tex-math></inline-formula> phase difference. Forty copper columns were mounted evenly along the circumference on the ground, which can enhance mid frequencies gain. To validate results, the designed antenna is manufactured and measured, which depicts a wide impedance bandwidth (IBW) of 110.4% (1.59-5.51GHz) and an axial ratio bandwidth (ARBW) of 111.4% (1.55-5.45GHz). Moreover, the antenna can contribute a stable gain in the 4G LTE band and a high gain in 5G new radio bands (n77, n78, n79) with compact size. And it achieves a peak gain of 6.6dBic at 3.55GHz. Compared with other similar designs, the proposed antenna owns good performance while being greatly miniaturized, and its volume is only 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda }_{l}$</tex-math></inline-formula> × 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda }_{l}$</tex-math></inline-formula> × 0.11 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda }_{l}$</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">${\lambda }_{l}$</tex-math></inline-formula> is the free-space wavelength at 1.59GHz).