Broadband Dual-Polarized Metal Lens With Theoretically Arbitrarily Variable Focal Diameter Ratio Using 3-D Printing Technology

Abstract

A wideband dual-polarized metal lens is proposed in this article for millimeter-wave (mm-wave) applications. Compared with the traditional lens, the focal length of the proposed novel metal lens can be of any value in theory; in other words, the focal diameter ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f/D$ </tex-math></inline-formula> ) can be arbitrarily adjusted. The metal 3-D printed technology is used to reduce the fabrication cost. The unit cell of the lens is a square open-ended waveguide. Since the phase velocity of the electromagnetic wave in the metal waveguide is faster than that in the air, the phase compensation can be controlled by adjusting the height of each unit of the lens. It helps to realize the conversion from the quasi-spherical wave of the feed source to the plane wave radiation of the lens. Due to the use of symmetrical elements, the lens can support different dual-polarized radiation (dual-linear polarization and dual-circular polarization). Considering the processing cost and design difficulty, a metal lens with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9\times $ </tex-math></inline-formula> 9 unit cells was processed to verify our design. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f/D$ </tex-math></inline-formula> is selected as 1. Simulated results for the lens antenna show a peak aperture efficiency (AE) of 43.8% and 38% for linearly polarized (LP) and circularly polarized (CP) radiation, respectively. The antenna shows a stable pattern and wide 3 dB gain bandwidth (26–40 GHz), which covers the entire Ka-band. The measured results of the lens demonstrate a peak gain of 24 dBi and 23 dBic for LP and CP radiation with an aperture of about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.5\,\,\lambda \times 7.5\,\,\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 free space wavelength at 30 GHz). The proposed lens features a wide gain bandwidth with dual polarization, low cost, and good radiation performance, which is well suited for mm-wave wireless applications.