Research And Design Of Horn Antennas Based On Stop And Pass Band Characteristics Of The Electromagnetic Band Gap

In recent years,the rapid growth in demands for wireless mobile communications has promoted the development of the fifth-generation mobile communications technology(5G).The capacity of the fifth-generation wireless network will increase by 1,000 times or more than 4G,and the use of the millimeter-wave(mm-wave)band is a key driving force for 5G to achieve this capacity increase,because the mm-wave band can provide continuous spectrums of over 1 GHz,as well as a data transmission rate of several gigabit-per-second(Gbps).On the other hand,the widely used conventional microwave frequency band is facing serious problems of spectrum congestion and exhaustion.The mm-wave frequency band has abundant available spectrum resources,which can effectively solve the system channel capacity limitation caused by the narrow bandwidth in the microwave frequency band.Due to the advantages of mm-wave band,high-performance mm-wave devices should be designed in communication systems.Also due to the disadvantages of rain attenuation and short transmission distance for mm-wave bands,it is necessary to design communication systems and related devices operating across microwave and mm-wave bands to make up for the shortages of mm-wave communications.In view of the above analysis,the main research contents of this paper are as follows:1.When a rectangular waveguide is connected to a mm-wave device,the tiny air gap caused by the not tightly connection has a great effect on the performance,and the same problem is also encountered in the interconnection of mm-wave devices.For the connection of practical mm-wave devices,it is difficult and expensive to fabricate them if tightly connections are ensured.Therefore,an electromagnetic band gap(EBG)structure in the E-plane was proposed,and a transition structure between gap waveguide(GW)and rectangular waveguide was designed based on this structure.The simulation results show that compared with the direct connection method,it has a better tolerance for air gaps that may be caused by machining or assembling.The fabricated transition structure shows a good performance.The testing results show that in the frequency band of 76.4-109.1 GHz(bandwidth 35.3%),the return loss is greater than 13dB,and the insertion loss is less than 0.6dB,which confirms the feasibility of this structure and that can be applied to the connections of mm-wave devices.2.Circularly polarized antennas are widely used in long-distance communication applications,such as radar systems,ionospheric research and satellite communications,because of their advantages of anti-polarization mismatch and multipath interference.A high-performance circularly polarized horn antenna is usually composed of a transmission line,a polarizer and a horn.The polarizer is small in the mm-wave frequency band,and often needs to be disassembled and fabricated;the connection of the various components of the antenna may also cause unnecessary power loss.Therefore,based on the design in research content one,a mm-wave broadband circularly polarized feed antenna based on EBG in the E-plane was proposed.The antenna is composed of a feeding waveguide,a rectangular waveguide to square waveguide converter,a polarizer,a square to circular waveguide converter,and a smooth-wall horn,and the EBG in the E-plane are added at each connection part.The polarizer is split into two parts for processing,and the split surface is added with EBG in the H-plane.The testing results show that the antenna has achieved a return loss of more than 20dB,an axial ratio of less than 2.5dB,an average gain of 19.18dBic,and a normalized sidelobe level of less than-25dB in the frequency band of 75-110GHz(bandwidth 37.8%).3.In order to further combine the advantages of long-distance and stable transmission in microwave bands with the advantages of broadband and high speed in mm-wave bands,a new type of dual-band transmission line:Band gap waveguide(BGW)was proposed.Its structure is composed of an internal Groove gap waveguide(GGW)and an external rectangular waveguide.The stop band of the EBG unit is used to confine the electromagnetic wave in the hollow channel area in the middle to propagate high-frequency signals;the pass band of the EBG unit is further used,so that electromagnetic waves can propagate at low-frequencies in the entire rectangular waveguide.After adding the transition structures,a back-to-back structure was fabricated.The testing results show that the transmission line works in low frequency band(6.8-8.05 GHz)and high frequency band(71-86 GHz),with good impedance matchings and low insertion losses in dual bands.On the basis of this transmission line,a dual-band antenna was further simulated and designed,and the low frequency microwave band has an average gain of 5.7dBi,while the high frequency mm-wave band has an average gain of 18.4dBi.