Investigations Of High-power Radial Line Helical Array Antenna

With the development of high-power microwave(HPM)technology,more attention has been progressively paid to the function of HPM antenna as the terminal of HPM system. Due to particularities of HPM,HPM antenna shall meet some special requirements as high-power capacity on the premise of ensuring favorable radiation.Therefore,many researches have been made at home and abroad,and such HPM antennas as mode converter with radiant horn,Vlasov antenna and mode-transducing antenna(like COBRA antenna,etc.) have been put forward.However,they are subject to some disadvantages more or less,and they can not perfectly meet the requirements of HPM system that become greater.Array antenna has its specific advantages applied in HPM field,which can probably solve many problems exist in HPM radiation.But the traditional array antenna can not be used directly into HPM field due to limit of power-handling capacity of power dividers and phase shifters. Based upon the above background,a new-type high-power radial line helical array antenna is put forward,and further theoretical analysis,numerical simulation,and experimental research have been carried out,through which,the feasibility of the design idea of the new antenna has been proved,antennas that fulfill high-power capacity,high efficiency,small size and circularly-polarized directional radiation have been realized and a new means for HPM radiation has therefor been provided.High-power radial line helical array antenna adopts short helical antenna which radiates circularly-polarized wave at its axial direction as radiation unit,uses radial line as feeding waveguide,applies new-type coupled probe to feed energy from radial line to unit antenna. Scheduled excitation magnitude and radiation phase can be reached by adjusting the coupling factor of the probes and rotating the radiation units,and in which way,directional radiation of microwave can be achieved.The whole antenna avoids occurrence of dielectric material and it is contained in a random placed upon the helical antennas to make it stay in vacuum and reach comparatively high power-handling capacity.The use of new-type coupled probe is one of the important technical innovations.The Paper focuses on idea of using new-type coupled probe instead of E-coupled probe,puts forward different probe forms including H-coupled probe and L-type EM coupled probe, analyzes the feasibility and advantage of them comparing with E-coupled probe,researches their basic coupling elements and coupling rules,and applies them on designs of high-power radial helical array antenna successfully. Theoretical elements related to the antenna are summarized and ameliorated systemically based upon the basic principle of high-power radial array antenna.The Paper focuses on the research of basic features of radial line and cylinder horn waveguide that involves filed equation,transmitting and cutting-off conditions of each mode,transmission power and attenuation constants,etc.,gives the description of radiation mechanism and far-field radiation field of cylinder helical antenna,analyzes the physical foundation of.axial mode helical antenna as phase shifter,the favorable radiation conditions of circularly-polarized wave conditions at axial direction of short helical antenna and analyzes the impact of unit polarisation on array antenna on the basis of basic elements of concentric array antenna.Mode matching method is used in the Paper for calculation of waveguide conversion procedures under the condition of that probes exist in the radial line and the relations between the orders of reflection mode and transmission mode and the number of the probes in conversion section are then obtained.Meanwhile,analysis over transmission features of production modes is made to obtain final results of the conversion procedures.In this way, production reasons and restraining conditions of high mode in radial line are known and the principle to be followed during the determination of array arrangement is determined.Coaxial-line to radial-line junction,unit antenna and array arrangement,etc.are optimized rationally to make them meet high-power application requirement,based on which,36-unit single-layer and double-layer radial-line helical array antennas are designed and experimental research on the latter one is made.It is shown from the experimental result that the antenna has a gain of 20.95dB,an aperture efficiency of 57.96%,a VSWR of 1.2 under 4.0GHz,and a gain over 20.2 dB,an aperture efficiency over 45%,a VSWR below 1.5 under the frequency range of 3.8～4.2GHz.The experimental result is consistent with the calculated one basically,which shows the feasibility of high-power radial line helical array antenna.Meanwhile,the impact of high mode on unit coupling capacity is revealed through comparison,and the advantages and disadvantages of single-layer and double-layer radial line feeding are analyzed.Analysis over power-handling capacity of 36-unit double-layer radial-line helical array antenna is made,which reveals that its power-handling capacity can not reach GW grade due to unequally-distributed field intensity of antenna aperture.Power-handling level of array antenna is improved through optimizing short helical antenna,improving form of coupled probe and optimizing array arrangement.Based upon the above,H-coupled 4-circle 48-unit radial helical array antenna and L-type E&M coupled 3-circle 48-unit radial line helical array antenna are optimized through simulations,and experimental researches on them are made.Simulated and experimental results are compared in the Paper,reasons for the differences in the results are discussed,and the relation between array arrangement and antenna performance is pointed out.It is shown from the experimental result of the latter that the antenna has a gain of 24.61dB,an axial ratio of 1.4dB,an aperture efficiency of 77.9%,a VSWR of 1.05 under 4.0GHz,and a gain over 23 dB,an axial ratio below 1.65dB, an aperture efficiency over 68%,a VSWR below 1.5 under the frequency range of 3.8～4.1GHz.At last,a high-power experiment for 3-circle 48-unit array antenna is made through using a GW level MILO as HPM source,which shows that its power-handling capacity exceed 1GW,and circularly-polarized directional radiation of GW level HPM is achieved finally.