Research On The Coupling Output Of Multichannel High Power Microwaves

As high power microwave (HPM) technologies gradually matured, the technologies for enhancing the output capacity of HPMs are becoming more and more attractive. Efforts have been made on increasing the output power, pulse duration, conversion efficiency and the frequency spectrum of the HPM devices. However, limited by physics and technology, the approaches for enhancing the output capacity with a single HPM source have encountered difficulties. An alternative method for enhancing the output capacity of HPM sources is taking advantage of coupling output of multichannel HPM sources. In this dissertation, a detailed research on the coupling output of multichannel HPMs is presented. The theoretical and experimental research results reveal that, the research on the coupling output of multichannel HPMs conceives a promising prospect for the development of HPM technologies. The detailed contents and innovative work are listed below.1. The filed-enhancement reduction and spatial-harmonic selection of the spatial-filtering diplexer for linearly polarized microwaves are investigated, and the coupling output of dual-channel gigawatt level HPMs is realized.In the dissertation, the plane wave expansion based mode matching method is employed for the analysis of the spatial diplexer consisting of rectangular rods. Based on this method, the influences of the external dimensions, frequencies of the incident waves, incident angles and the other factors on the performances of the diplexers are obtained. Some experiments on the diplexer consisting of rectangular rods have been carried out in our laboratory. The preliminary experiments reveal that, the diplexer exhibits a good performance for the coupling output of S/X band HPMs, however, affected by the field enhancement of the rectangular rods, when the microwave power increase to 2.0GW with pulse duration of 30ns, the pulse shortening and surface flashover are observed.In order to design a practical diplexer for high power, long pulse operations of S/X band HPMs, a diplexer consisting of cylindrical rods is proposed and employed in the HPM coupling output system. The corresponding rules for selecting the spatial harmonics of the scattered waves generated by the cylindrical-rod array are obtained. In the further low power and high power experiments, the designed diplexer consisting of cylindrical rods exhibits a relatively better performance for the coupling output of S/X band microwaves. The reflection and transmission efficiencies are as high as 97% and 97.5%, respectively. When the diplexer consisting of cylindrical rods is illuminated with 1.8GW HPMs of 100ns duration, no microwave breakdown has been found. For the sake of validating the feasibility of the simultaneous operation of S/X band high power microwaves, the high power performances of the diplexers consisting of cylindrical rods which are immersed in dielectric environment are discussed. The results reveal that, the diplexer consisting of cylindrical rods immersed in SF6 gas is capable of being applied for the simultaneous operation of S/X band HPMs with power level of 5.5GW.2. The enhancement of both the power handling capacity and transmission efficiency and the suppression of the higher order modes in the waveguide-filtering diplexer are studied, and the coupling output of dual-channel gigawatt level HPMs in the same frequency band and polarization direction is realized.According to the characteristics of TEm0 mode, an important concept to enhance the power handling capacity of the waveguide components consisting of H-plane discontinuities by enlarging the heights of the main waveguides without any affects on its transmission properties is proposed. A prototype waveguide diplexer is designed and analyzed systematically by the finite element method. The numerical calculations reveal that, the designed diplexer has its transmission efficiency higher than 98% at 9.38GHz and 9.60GHz, the frequency bands with efficiency higher than 90% are more than 120MHz. The low power experiments show that, the transmission efficiencies are higher than 97% at 9.38GHz and 9.60GHz separately. The frequency band with transmission efficiency higher than 90% is more than 100MHz, which is in agreement with the numerical simulation. In the high power experiments, the radiated powers of the beat waves are measured to be about 4.3GW, 40ns, the frequencies are about 9.41GHz and 9.59GHz. These results demonstrate that, the diplexer is applicable to the generation of GW level beat waves and the power combining of HPMs.3. Based on the previous work, the hybrid filtering method is employed to realize the coupling output of multichannel HPMs. As an example, the coupling output of the S/X/X band HPMs is investigated for the validating of this method. The theoretical analysis reveals that, when the spatial filter is immersed in SF6 of 1atm, the ultimate power handling capacity of the multichannel coupling output system reaches over 10GW. The further experiments are designed for the operations of the 3.6GHz, 9.41GHz and 9.59GHz HPM sources. The low power experiments reveal that, the transmission efficiencies of each channel from the feeding port to the radiating port are as high as 96% for the operation frequencies. When fed with GW level HPMs, there is no obvious microwave breakdown. Thus, the feasibility for the coupling output of S/S/C/C/X/X band six-channel HPMs is preliminarily demonstrated.4. The feasibility for the coupling output of circularly polarized microwaves is discussed in the end. The improved strip circular polarizer and the diplexer for circularly polarized microwaves are employed for the coupling output of circularly polarized HPMs. With theoretical analysis and numerical simulation, the coupling output of S/X band four-channel circularly polarized HPMs is preliminarily validated.