The Research On Broadband And High-Gain Planar Array Antenna

To meet the various engineering application requirements in long-distance communication systems,such as high data transmission rate,portability,low profile,lightweight,and low cost,antennas,as a important transceiver component,have been increasingly demanded.Among kinds of antennas,planar array antennas have been the research focus in recent years due to their intrinsic advantages of low profile,good portability,and easy assembly,as well as the given features of wide bandwidth,high gain,high aperture efficiency,and low side lobe levels.This dissertation focuses on the discussion and research on passive planar array antennas,with resonant antennas as radiating elements.The design issues of wide band,high gain and large-scale array realization is mainly studied.Three planar array antennas and a linear series-fed array antenna are designed,as follows:1.To achieve high aperture efficiency for a large-scale planar array,a cavity planar array antenna is proposed with a sandwich structure.By sharing the metal surfaces,the profile of the array employing the proposed structure is reduced.Furthermore,a highefficiency antenna element is realized at a low price by using the sandwich structure.Firstly,the topology of the hybrid waveguide-microstrip feeding network is discussed and analyzed.The transition structure is deeply analyzed for improving high transmission loss between two transmission lines.An equivalent-circuit model is developed to provide an insight on the transition structure and explain the principle of loss suppressing.By introducing a rectangular patch with four corners shorted on the transition structure,the transmission loss is reduced by about 0.8 d B.Then,a cavity-backed antenna using top feeding is designed.The design ideas and evolution process of the antenna are explained.By conducting a comparison among the proposed antenna element,a microstrip antennas and a conventional cavity-backed slot antenna,the working principle and advantages of the proposed antenna are demonstrated.Finally,an 8 × 16 array is fabricated and tested.The results show that the proposed array achieves a relative bandwidth of 20.8%,a high gain of 28.8 d Bi,and a high aperture efficiency up to 86.1% in the Ku band.2.To solve the challenge of designing planar arrays with special dimensions and significant gain,a millimeter-wave planar array antenna with a large aspect ratio based on series-parallel feeding is studied and proposed.It is the first reported planar array design with such a large aspect ratio.The array has a aspect ratio of 6.25:1,a low side lobe level of-20 d B and an significant gain of 33 d Bi with a aperture efficiency over 60%.This proposed array adopts parallel feeding in the long side direction using a metal Eplane waveguide,which can effectively suppress the leakage of electromagnetic waves from gaps between metal structures and reduce assembly complexity.The waveguide power divider network is designed with an unbalanced structure to achieve parallel feeding outputs that satisfy the Taylor amplitude distribution.The top radiating elements are microstrip patch antennas,which are fed in series to achieve a compact size and meet the requirements of the specific aperture design.The bottom waveguide feeds the top seriesfed microstrip antenna subarrays.The waveguide-to-microstrip transition structure is designed to further reduce the insertion loss at the expense of shortening the bandwidth,with a transmission coefficient of-0.2 d B in the millimeter-wave band.Based on the designed E-plane waveguide network and series-fed microstrip antenna subarrays,a 64 × 12 planar array is realized and tested.The results verify the effectiveness of the design method.3.A novel magnetic current feeding method is proposed to enhance the bandwidth in planar array design.The mechanism of the current feeding and the proposed feeding are described and demonstrated.Based on the working mechanism and equivalence principle,an antenna element and 6-element series-fed array with magnetic current feeding structures are presented,respectively.By testing the fabricated 6-element array antenna,it shows that the proposed method can introduce an additional resonance point in the frequency band,achieving a wide band.Finally,based on magnetic current feeding,hybrid feeding network,and gap waveguide technology,an all-dielectric wideband planar array antenna for the millimeter-wave application is proposed.To address the challenge of low-cost and lightweight requirements,the antenna is designed using substrate integrated gap waveguide,which provides low-loss transmission.The proposed gap waveguide consists of three layers of FR-4 substrates.Double-sided mushroom electromagnetic bandgap(EBG)structures are employed in the gap waveguide and antenna elements to suppress the leakage from gaps between substrates.The utilization of EBG structures eliminates the need of soldering process and simplifies the array assembly.The magnetic current feeding method is employed in the design of radiating elements,and a significant improvement in bandwidth is demonstrated compared to that of the microstrip-fed element.Based on the substrate integrated gap waveguide and wideband substrate integrated cavity elements,an8 × 8 array with four layers of FR-4 and a layer of high-frequency substrates is proposed,fabricated and tested.The usage of FR-4 substrates effectively reduces the manufacturing cost.The results show that the array achieved a impedance bandwidth of 32.9% and a aperture efficiency varying from 55% to 79% within the operating band.