Compact and Gain-Enhanced Directive Endfire Higher-Order-Mode Meander Dipole via Asymmetrically Loading Stubs

A directive planar endfire antenna with high gain and miniaturized size is proposed. By utilizing the higher-order-mode currents of the dipole, the antenna achieves the endfire radiation pattern without parasitic elements (directors or reflectors) loading. The antenna keeps the position of the current null at the bend, and the higher-order-mode currents change to both forward and reverse directions by meandering. It utilizes loading stubs to get the desired phase difference between each section of higher-order-mode current, resulting in a compact endfire 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">$0.15\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> is the wavelength at the lowest frequency in free space) and a measured high gain of 6.28 dBi. Furthermore, by merely introducing a sawtooth director, the quasi-Yagi antenna has a compact 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">$0.38\lambda $ </tex-math></inline-formula> and a measured endfire gain of 8.32 dBi without a reflector. Both antenna operation frequencies cover the industrial, scientific, and medical (ISM) 5.8-GHz (5.725–5.875 GHz) band. The proposed antennas are excellent candidates for portable device systems that require miniaturization and high gain.