Designs of Magnetoelectric Dipoles in the Millimeter-Wave Band

在毫米波頻段的磁電偶極子設計

Student thesis: Doctoral Thesis

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Award date2 Oct 2019

Abstract

This thesis presents some novel designs of magnetoelectric dipoles (ME-dipoles) for use as antennas and metasurfaces at millimeter-wave (MMW) frequencies. These ME-dipoles are excited by three techniques: aperture excitation and transmission line excitation (TLE) for antennas and free-space excitation for metasurfaces. The use of ME-dipoles enabled all designs to exhibit wide operating bandwidths, and all antennas possess stable antenna gains and stable radiation patterns with low cross-polarization and low back radiation. Because the antennas incorporated substrate integrated waveguides (SIWs), they were easy to fabricate and operate at MMW frequencies.

First, an aperture-coupled ME-dipole antenna is developed to generate broadside circularly polarized (CP) radiation. The antenna consists of a cylindrical cavity, an electric dipole, a pair of metalized vias and a slot etched on the upper broad wall of a short-ended SIW. This ME-dipole is excited by the aperture of the etched slot of the SIW. A prototype was fabricated by using printed circuit board (PCB) and plated-through-hole (PTH) technologies. Measurements show that the proposed antenna can achieve an overlapping impedance and axial ratio (AR) bandwidth of 21.9% from 53.6 to 66.8 GHz with a broadside right-handed CP (RHCP) gain from 5.3 to 8.6 dBic.

Second, another aperture-coupled ME-dipole antenna is developed to generate end-fired CP radiation. Its operating mechanism is like that of the last one. The antenna element consists of an open-ended SIW, an electric dipole, a double-sided parallel-strip line (DSPSL), and two metal blocks. This ME-dipole is excited by the aperture of the open end of the SIW. It has a simple configuration and can achieve wide impedance and AR bandwidths, stable gain, and radiation patterns, as well as having low back radiation. To increase the gain, a 1×8 antenna array is formed by integrating eight antenna elements with a planar 1-to-8 SIW feed network. A prototype was fabricated by using a single-layered PCB with PTH technology and metal blocks. Measurements show that the proposed antenna can achieve an overlapping impedance and AR bandwidth of 23.8% from 56.3 to 71.5 GHz with an end-fire left-handed CP (LHCP) gain from 14 to 15.3 dBic.

Third, a series of TLE ME-dipole antenna arrays are demonstrated with differential feeds. Each proposed antenna is composed of ME-dipole arrays enclosed by a cavity. Each ME-dipole is excited by a transmission line in the form of a coplanar stripline (CPS) on the top metal layer of the PCB. The first design is introduced to illustrate the potential of the TLE technique to realize a broadside ME-dipole array by using a single-layered PCB. The second TLE ME-dipole antenna array design is developed from the first design to generate CP radiation. Two more TLE ME-dipole antenna array designs are also developed from the first design to achieve higher gains. A novel differential feed network was introduced to measure these differentially fed antennas. Measurements show that the proposed antennas retain all of the salient features of ME-dipoles, in having broad bandwidths and stable broadside gains, as well as stable radiation patterns with low cross-polarization and low back radiation.

Fourth, a set of ME-dipole metasurfaces are proposed. Each metasurface is composed of two layers of PCBs. For the unit cell of each metasurface, there is a slot on the middle metal layer with an ME-dipole on its each side. Each ME-dipole comprises four metalized vias and four metallic patches with a strip/cross-strip. The first metasurface is a frequency selective surface (FSS). It is introduced to illustrate the potential of the ME-dipole in metasurface designs. One of the linearly polarized (LP) ME-dipole of the FSS unit cell is replaced with a CP ME-dipole to form a linear-to-circular polarizer as the second proposed ME-dipole metasurface. The lengths of the patches and the slot of the FSS unit cell are simultaneously tuned to change the transmission phases to form a transmitarray as the third ME-dipole metasurface. Measurements show that the proposed metasurfaces retain the salient feature of ME-dipoles in having broad bandwidths.