Research On The Technology Of Air-Fed Phase-Shifting-Surface Array Antennas

The high-gain antenna is one of key components in wireless systems such as radar,satellite communication,and space exploration.With the rapid development of wireless technology,the performance,size,and weight of antennas are increasingly required.Air-fed phase-shifting-surface arrays combine the characteristics of classical air-fed antennas and microstrip array antennas,they have been widely concerned by many scholars at home and abroad because of their simple structure,low profile,easy machining,and flexible beam design.Air-fed phase-shift-surface array antennas are expected to become a new choice to replace the classical air-fed antennas and microstrip array antennas in some fields in the future,so the research of air-fed phase-shift arrays has far-reaching significance.This dissertation focuses on the transmitarray（TA）antenna,including the high-efficiency TA and wideband TA,tri-band transmit-reflect array,dual-band TA with independent polarization control,dual-band low-profile air-fed arrays,polarization-decomposition TA and mode-conversion TA.The main innovations of this dissertation are summarized as follows:1.A high-efficiency dual-linearly polarized TA is designed.The element comprises only two layers of patches printed on a dielectric substrate and four vias.Through the combination of cross dipole and spiral dipole,the 360°phase shift range is achieved.To improve the transmission efficiency,symmetrical metal vias and L-shaped patches are introduced.The transmission magnitude is kept within-1 d B,showing low-loss characteristics.A square TA using this element is designed.The experimental results show that the TA has a gain of 29.18d Bi at 14.25 GHz,and the corresponding aperture efficiency（AE）is 60.3%.The 1 d B gain bandwidth of the antenna is 6.8%.2.A metal-only wideband TA is designed.The element is made of metal only,avoiding the performance instability that can be caused by using dielectric substrates,enabling it to be used in more stringent environments.The element consists of three pure metal layers,the upper and lower layers are polarizer grid layers,and the middle layer is the polarization-conversion layer.After passing through the upper grid,the polarization of the incident wave is rotated by the middle polarization-conversion layer and then is radiated again from the lower grid.The phase of the outgoing wave can jump 180°by rotating the polarization-conversion layer 90°,which extends the phase-shift range.The bandwidth of element transmission magnitude within-2 d B is 6 GHz（12 GHz to 18 GHz）and the phase is linear,which is conducive to the wideband design of TA.The final TA designed with this element achieves a peak AE of 46.8%and a 1 d B gain bandwidth of 20.5%.3.A multifunctional tri-band bidirectional-radiation transmit-reflect array is designed.Through the clever integration of cross dipoles with the ground and double square rings,a bidirectional-radiation air-fed array with transmission at Ku-band and reflection at K and Ka-bands is designed.The antenna has dual-polarized characteristics in each band.The experimental results show that the TA achieves a peak AE of 40%in the Ku-band,and the 1d B gain bandwidth is 6.5%.In the K-band,the peak AE is 44%and the 1 d B gain bandwidth is 7.3%.In Ka-band,the peak AE is 47%and the 1 d B gain bandwidth is 7.1%4.A dual-band dual-polarized TA with independent control of polarization is designed.Cross dipoles and rectangular patches are utilized to control the transmission characteristics at Ku and K-bands,respectively.The phases can be controlled independently at both bands because of the band independence of the element.The vertical polarization（VP）and horizontal polarization（HP）phases at each band can also be controlled independently because of the polarization independence of the element.Under horizontally or vertically polarized excitation,the beam directions of the designed TA are（30°,0°）and（-30°,0°）at13.5 GHz,and（30°,90°）and（-30°,90°）at 22 GHz.The antenna is fabricated and measured,and the experimental results are in good agreement with the simulated results.5.A low-profile dual-band circularly polarized（CP）air-fed array is designed.The antenna consists of a folded TA operating at the K-band and a multi-feed reflectarray（RA）operating at the Ka-band.The dual split rings are used as the TA and RA elements.The TA is placed above the RA.The TA acts as the phase-controlling surface at the K-band and does not affect the transmission of plane waves at the Ka-band generated by the RA.The RA simultaneously serves as the phase-controlling surface at the Ka-band and as the ground for the folded TA at the K-band.The combination of the folded TA and multi-feed RA has a low profile,and the height-to-diameter ratio is only 0.4.The CP patch arrays integrated on the TA surface are used as the feeds in this design,to avoid the complex feed structure of the traditional horn+orthomode transducer（OMT）+circular polarizer,which significantly saves space and cost.The measured results show that the 3 d B gain bandwidths of antenna are 7.2%and 7.3%,and the peak AEs are 22.8%and 22.6%,respectively,at K and Ka-bands.6.A low-profile dual-band linearly polarized folded TA is designed.The dual-band elements consist of orthogonal and interlaced receive-transmit strip patches.Due to orthogonal isolation,the patches of the two bands hardly affect each other.The feed is a dual-band orthogonally polarized patch integrated on the TA,which avoids the use of some waveguide structures.The pure metal is used as the ground of folded TA,and the antenna profile can be reduced by 1/2 by placing the feed on the TA layer.The height-to-diameter ratio of the antenna is only 0.3.The 1 d B gain bandwidths of the antenna are 7.3%and 4%,and the peak AEs are 27%and 24%,respectively,at Ku’s upper and lower bands.7.Polarization decomposition and mode conversion are carried out by the receive-transmit TA.Firstly,the proposed receive-transmit element is analyzed,and it is concluded that the incoming linearly polarized（LP）wave can be decomposed into outgoing left-handed and right-handed circularly polarized（LHCP and RHCP）waves,and the phases of LHCP and RHCP waves are composed of the initial phase and rotational phase.Then,the LHCP and RHCP phases can be compensated independently and simultaneously by adjusting the initial and rotation phases of the element,which means that the LHCP and RHCP beams of the TA can appear simultaneously in different positions in space.Finally,a dual-circularly polarized dual-beam TA with linearly polarized feed is designed,the LHCP and RHCP beam directions are（30°,0°）and（0°,0°）respectively,the gains of the measured LHCP and RHCP beams at20 GHz are 25.7 d Bic and 26.1 d Bic,respectively.The designed antenna can be applied to multibeam coverage under different polarizations and point-to-multipoint microwave systems.Through analysis,it can also be concluded that the incoming LP wave with arbitrary polarization angle can be rotated into the fixed-polarized outgoing LP wave by the element,and the phase of the polarization-conversion beam can be compensated by the initial phase.Thus,a TE₀₁-to-HE₁₁ mode-converting TA and a TM₀₁-to-HE₁₁ mode-converting TA are designed.The gains of TE₀₁ and TM₀₁ mode-conversion TA are 29.68 d Bi and 30.2 d Bi at20 GHz,respectively,and the corresponding AEs are 53.2%and 59.8%,respectively.This TA can avoid the introduction of complex mode converters in a high-power system.