Circularly Polarized Broadside Beam Radiated From a Large, Low-Profile Metaloop Antenna

Abstract

The area within a loop antenna can be used for inserting additional components (such as mounting hardware) if this does not cause the antenna characteristics to degrade. This article discusses a circularly polarized (CP) metaloop antenna that has a loop circumference of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C} _{\mathrm {LOOP}}= 1 \lambda _{\text {g}}= n\lambda _{0}$ </tex-math></inline-formula> with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n&gt;1$ </tex-math></inline-formula> , thereby creating a large area within the loop, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\text {g}}$ </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">$= 2~\pi /\beta $ </tex-math></inline-formula> ) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </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">$= 2~\pi /k_{0}$ </tex-math></inline-formula> ) are the guide wavelength of the current on the loop and the free-space wavelength, respectively. Values for the propagation phase constant within the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-1 &lt; \beta /k_{0} &lt; 0$ </tex-math></inline-formula> are used in this article. It is found that metaloop antennas for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n = 3$ </tex-math></inline-formula> , 4, and 5 generate a CP broadside beam (axial beam) with gain bandwidths (GBWs) of approximately 6%, 5%, and 4%, respectively. The VSWR across the GBWs is less than two and the axial ratio is less than 3 dB. The radiation efficiencies for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n=3$ </tex-math></inline-formula> , 4, and 5 are approximately 48%, 69%, and 83%, respectively. When a conducting disk (as a generalization for the presence of additional components) is inserted into these metaloop antennas, the antenna characteristics are not degraded until the disk and the metaloop are in close proximity (proximity coupling occurs).