Broadband Antennas And Arrays For Millimeter-wave Wireless Communications

Recently,with the rapid development of mobile communications,there are more and more demands for higher data rate,and much more requirements for frequency spectrum to support new communication services.To meet these demands and requirements,the millimeter-wave(mm Wave)wireless technology is one of the hottest research areas for the up-coming 5th generation mobile communication systems(5G).As the antenna is one of the most essential devices of mm Wave communications,the studies and applications of antennas and arrays need to be widely and deeply carried out.This dissertation focuses on the study of broadband antennas and beamforming reflectarrays for mm Wave wireless communications,and the dissertation is organized as follows:First,a low-profile wideband antenna with the broadside radiation pattern is proposed based on the theory of microstrip antenna,which overcomes the challenge of the narrow bandwidth for the conventional microstrip antenna.As one of operation mode for the patch antenna,the TM₁₀ mode can realize a broadside radiation pattern,but the conventional TM₂₀mode cannot.To achieve a broadside radiation pattern,a longitudinal slot is etched on the patch,which changes the original E-field distribution of the TM₂₀ mode and rarely affects the E-field distribution of the TM₁₀ mode.This longitudinal slot leads to the broadside radiation pattern for modified TM₂₀ mode without affects broadside radiation pattern for TM₁₀ mode.Moreover,two symmetrical transverse slots are etched on the patch to suppress TM₁₂ mode,which has a small effect on the two designed modes and further broadens the bandwidth of the radiation pattern.The proposed antenna with one longitudinal slot and two transverse slots has a symmetrical E shape,which can achieve 45.6%impedance bandwidth for|S₁₁|less than-10 d B and features a stable pattern with less than-16 d B for the cross-polarization during the working bandwidth.The peak gain and the 3-d B bandwidth of the antenna are 8.5 d B and larger than30%,respectively.Furthermore,a cross-slot quadrate patch is proposed using the multimode resonance,and an 8×8 planar antenna array is designed using the proposed patch,which realizes29.3%working bandwidth and 26.3 d Bi peak gain.Then,a broadband endfire magnetoelectric(ME)dipole antenna array with the substrate-integrated coaxial line(SICL)is proposed based on the theory of ME dipoles.The broadband feeding network and broadband antenna are designed respectively and then combined together,which overcomes the challenge of the broadband endfire antenna array design.The influence of defected ground structure for the ME dipole and the planar L-probe are studied,and the broadband endfire ME dipole with a defected ground is proposed.The proposed broadband endfire ME dipole with defected ground structure is excited by a planar L-probe,which can achieve 53.0%impedance bandwidth.By the broadband impedance conversion and T-shaped power divider structure,a 16-way low loss SICL feeding network is designed,which achieves109.6%working bandwidth with the|S₁₁|less than-10 d B and the insertion loss less than 13.4d B.A 1?16 endfire antenna array is designed by combining the proposed antenna element and feeding network.The array has 57.6%bandwidth for the|S₁₁|less than-10 d B,and 54.5%bandwidth for the 3-d B gain bandwidth,while the peak gain is 19.0 d Bi.Next,the independently controllable orthogonal dual-linearly-polarized reflectarray antennas are proposed,which overcomes the challenge of the realization for independent dual-linearly polarized control.Based on the principle of the 1-bit unit cell,a broadband 1-bit reflective unit cell with reconfigurable potential is proposed by controlling the frequency of the magnetic resonance and the electrical resonance,which achieves 61.6%working bandwidth for the 180±20-degree reflective phase difference between two states.Within this working bandwidth,the cross-polarization is less than-30 d B with high polarization isolation.Using the proposed unit cell,the spatially separated dual-polarized reflectarray antenna for 45-degree incident waves and the independently controllable dual-polarized reflectarray antenna are respectively designed.The first one can separate 45-degree incident waves into-15-degree horizontally polarized reflective waves and 25-degree vertically reflective polarized waves.For the horizontal polarization,the peak gain and the 1-d B beamwidths are 23.5 d Bi and 14.5%,respectively.For the vertical polarization,the peak gain and the 1-d B beamwidths are 24.2 d Bi and 11.4%,respectively.The second one can realize-15-degree beamforming for horizontally polarized incident waves and 20-degree beamforming for vertically polarized incident waves.The gains at 33.0 GHz are 25.0 d Bi and 25.8 d Bi for the horizontally polarized beam and the vertically polarized beam,respectively.The 1.5-d B bandwidths for both polarizations are20.6%.Finally,a pre-phased 1-bit reflective metasurface is proposed based on the theory of array synthesis,which alleviates the inherent limitation of single-beam forming for the conventional1-bit reflective metasurface under plane incident waves.The normally incident plane waves are discussed as an example.A theoretical analysis is presented to show that,under the normally incident plane waves,single-beam patterns can be achieved by introducing a fixed pre-phase distribution with two values in the 1-bit metasurface.Compared with conventional 1-bit reflective metasurfaces,the proposed scheme alleviates the inherent limitation of single-beam patterns on 1-bit reflective metasurfaces under the normally incident plane waves.To verify the proposed scheme,three pre-phased 1-bit reflective metasurfaces with single beams pointing separately at 0,15,and 30 degrees are designed for normally incident plane waves.The simulated and measured results show that the proposed pre-phased 1-bit metasurface can achieve single-beam patterns under normally incident plane waves.