Investigations Of High Power Linear Polarized Radial Waveguide Array Antenna

With the development of high-power microwave (HPM) technology, the HPM antenna has become an important part of the HPM system. Due to paticularities of HPM, HPM antenna shall satisfy some special requirments.At the early times, slot antennas which can radiate linear or circular polarized waves by certain arrangement are used as cells of the radial line array antenna. Patch microstrip antennas and low-profile helical antennas are used later. As there are slow wave structures and media in this kind of array antennas, they can't be used in HPM areas. However, with the development of HPM antenna, a novel HPM radial line helical array antenna as a new kind of HPM antennas is proposed recently. In this antenna, a new kind of coupling probes is adopted which avoid the presence of media. These characteristics of the probe establish base for design of high-power radial line array antenna. At the same time, this antenna as a new means for high-power microwave radiation can fulfill high-power capacity, high efficiency, miniaturized. But this array form realized circular polarized radiation only, therefore HPM linear polarized radial line array antenna becomes another important aspect in research. In this paper, HPM linear polarized radial line array antenna is proposed firstly on the basic of radial line feed, and series of exploration and research are made in this paper.The novel coupling probe requires the feed port of the cell antenna is coaxial feed, so linear polarized cell of coaxial feed become the most inportant aspect of the reseach. At first, series of requirements to the linear is proposed to the cell based on the radial line feed system and characteristic of the whole array antenna. Then, in the area of the linear polarized antennas are investigated based on the requirements in these two aspects:(1) a lot of basic antenna shapes including dipole and loop antennas and their new form etc. are investigated; (2) antennas of linear polarized radiation composed by circular polarized antennas are investigated on the other side. Finally, a planar single circular linear polarize antenna is chosen which satisfies each characteristic as a radiation cell by contrast.To realize the characteristic of the maximal radiation in coaxial direction and satisfy the requestment of linear polarized stimulation, single circular grid radial line array antenna which has a simple form becomes the best choice. In this array, each radial position of the probes is the same and the magnitude and the phase of coupling waves is the same. As the number of the array cell is limited, the gain of the antenna is low. To improve the gain, the number of the cells and the circles is need to increase, as a simple single circular grid can't meet all the requestments. However, there is a most important question when using multi-ring grid array to realize HPM linear polarized radial line array antenna. Only when the distance of the wave path of the radial lines isλ(wavelength in the waveguide), the differencing of coupling wave phase is±2π(as a matter of fact, it's the same), it is possible to realize highest resultant field intensity of the maximum of the linear polarized radiation on these positions by regulating the amplitude of the coupling wave and simulating the same cells; On the other side, from the characteristic of the planar array antenna it is known that when the spacing isλ(wavelength in the waveguide), there are more than one grid lobes appear. To restrain the grid lobes, the distance of the cell must be reduced which make the coupling port have some phase differencing.(which is not equal±2π), simulate on the same radiation cells cannot realize same magnitude and phase simulation. To improve the gain of the array antenna, this is the most important question.To solve this question, this paper proposed two solutions to the key problem by analyzing. Solution 1:Radial line is fed in series, in this project, the layout of circular grid is still adopted, while the radial line bent to a certain extent which is in order to increase the wave-path in the internal of the waveguide. There can be 2πphase-difference among different circles by adjusting the dimension properly, finally the linear polarized antenna is excited by the excitation with equal amplitude and phase. Solution 2:Radial line is fed in parallel, in this project, In order to make every microwave route in the feed system have the same wave-path, grid form of array antenna is changed and multi-layer feed is adopted. Finally the excitation of linear polarized element antenna is in-amplitude and in-phase.As the effect of complex wave mode characteristics of the bend radial line and the coupling probes, the analysis of first solution is difficult. So second solution is investigated in this paper, combined with the horizontal ring cell antenna, parallel connection feed HPM linear polarized radial line array antenna is formed. Meanwhile, theoretical elements related to the antenna are summarized and ameliorated systemically based on the basic principle in this paper including these aspects:the connection between the overall arrangement of the array and antenna performance is analysed, basing on this analysis, parameters in the array design are abtained; characteristics of the microwave high frenquency are comprehend; the infection to S11 parameter by the mode in the coaxial-line-radial-line junction is theoretic analyzed and calculated, knowledge about this structure is deeply recognized which establish theoretical base for the mode analysis of the whole array antenna.Base on this reasonable design of the primary power divider, array unit divider and the cell antennas etc, numerical simulation and measurement of the HPM linearly-polarized radial line array antenna of L-band is simulated. Simulation results indicate that this structure is feasible to realize the linear polarized radial waveguide array antenna. The Gain of the antenna is 19.97dBi at the frequency of 1.57GHz, The aperture efficiency is 50.5%,the axial ratio is-52.06dB. In the range of 1.37 GHz to1.77 GHz, the gain is over 18.64dBi, The aperture efficiency is above 37.2%, the axial ratio is below-46.45dB; In the range of 1.53 GHz to 1.76 GHz, the reflecting coefficient is below 0.2 (which is the same as VSWR is 1.5). The resules above prove that this antenna is feasible, but there are some questions in this antennas, the reflection of this antenna is a little high and the aperture efficiency is low, the power capacity is not big enough. To solve these questions, optimum simulation is carried on in the chapter 5. The simulation results indicate that the Gain is 18.8dBi at the central frency of 1.57GHz, the aperture efficiency is above 64.26%,the axial ratio is-40.07dB, in the range of 1.37 GHz tol.77 GHz, the Gain is over 17.58dBi, the axial ratio is below-40.07dB, in the range of 1.17 GHz to 1.68 GHz, the reflecting coefficient is below 0.2(which is the same as the VSWR equals 1.5); the power capacity can reaches 1GW.Finally, experiment is carried on the basic of the results of the numberical simulation. It shows that on the central frequency of 1.57GHz, the gain of the array is 17.65dBi, the aperture efficiency is 58.6%, the VSWR is 1.19; In the range of 1.47 to 1.77 GHz, the Gain is over 17.31dBi, the axial ratio is below-38.6dB. The aperture efficiency is over 54%, and the VSWR is lowre than 1.4. The experimental results is almost accorded with simulated results which means that HPM radial line array antenna can meet the property of a linear polarized radiation.