Compact and Wideband Crossed Dipole Antenna Using Coupling Stub for Circular Polarization

Abstract

A novel compact and wideband circularly polarized (CP) crossed dipole antenna is presented. To realize CP radiation, a new design concept of using coupling stub is first illustrated. The coupling stub is equivalent as a combination of a dipole- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${c}$ </tex-math></inline-formula> and dipole- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> . The dipole- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${c}$ </tex-math></inline-formula> not only couples proper energy from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> -axis arranged driven dipole- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> to the orthogonally arranged dipole- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> but also provides quadrature phase delay to the dipole- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> . Therefore, CP radiation is realized for the presented configuration. To improve the input impedance caused by the strong coupling, a long narrow strip is incorporated for the enhancement of impedance bandwidth. Based on the design concept, a compact and wideband CP antenna by using the coupling stub and stepped square loop is developed to further increase the operation bandwidth and realize stable radiation. The designed antenna was finally fabricated for performance verification. Both the simulation and measurement show that the developed antenna can have a wide overlapped impedance and axial ratio (AR) bandwidth from 1.1 to 1.74 GHz with a compact radiator size. In addition, stable antenna gain and radiation patterns are achieved for wireless communications.