Investigations Of Square Radial Line Helical Array (Sub-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, 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. Therefore, many researches have been made at home and abroad, and such HPM antennas as mode converter with radiant horn, Vlasov antenna, mode-transducing antenna and High-power radial line helical array antenna have been put forward. The antennas mentioned above have their own characteristics. By analysis and comparison we find High-power radial line helical array antenna have some special advantages, which can probably solve many problems exist in HPM radiation. But this antenna can not meet high gain because the probe coupling energy can not regulate arbitrarily. Based upon the above background, the design idea of a new assembled high-power high-gain array antenna is put forward. And then, focused on its key part——square radial line sub-array antenna, theoretical analysis, numerical simulation, and experimental research have been carried out, through which, the feasibility of the design idea of the anew assembled antenna has been proved, and the sub-array model fulfills high efficiency, small size and circularly-polarized directional radiation.The assembled high-power high-gain array antenna is combined with many square sub-array, which 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 coupling 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.Theoretical elements related to the square sub-array antenna are summarized and ameliorated systemically based upon the basic principle of high-power radial array antenna. The Paper focuses on the far-field radiation field of rectangular array antenna, the research of basic features of radial line, the favorable radiation conditions of circularly-polarized wave conditions at axial direction of low-profile helical antenna and the three plane mode match technique is applied to model the generalized S parameters of coax-waveguide T junctions. In this way, design principles are obtained. Coaxial-line to radial-line junction, unit antenna and array arrangement, etc. are optimized rationally to make them meet requirement of the square sub-array, based on which, a helical assembled square array antenna of 16 elements using L—haped coupled probes is put forward, which is combined with 4 helical square array antennas of 4-element and a 4-way radial line equal power divider.Numerical simulation and measurement are accomplished in detail. Measured result shows that in the range of 3.75 GHz to 3.95 GHz, the directivity is upon 17.5 dB, and the VSWR is below 1.3. But due to the radiation phase of each helix is same, reflectance and axial ratio of the array is not ideal.For the disadvantage mentioned above, an improved model of 16-element helical square array antenna fed from single radial line is designed. A new type of one side post coupling probe and L-shaped probe are used to feed energy from radial line to unit antenna. The experimental research shows that in the range of 3.8 GHz to 4.2 GHz, the directivity is upon 17 dB, and the VSWR is below 1.3, the aperture efficiency is upon 74%, and the axial ratio is below 1.3 dB. Meanwhile, through comparison, and the advantages and disadvantages of the two models are analyzed.