The high power microwave (HPM) synthesis method is presented in this paper for gigawatt level. The gigawatt level HPM could be synthesized from two separate input wave-guides according to the coupled-wave and orthogonal polarization theory. The synthesizer is used by two back to back circular wave-guides. The main channel is the circular wave-guide connected to the output port, which transmits horizontal polarization TE 0 11 mode. The operating bandwidth is only limited by the barrier wave-length λ c of circular wave-guide. The sub-channel transmits vertical polarization TE 0 11 mode and the operating bandwidth is up to several hundred MHz. The energy of sub-channel could be coupled into main channel through continuous long-slit coupling structure. The synthesizer can be analyzed using numerical simulation method, which focuses on the power capability. The simulation results indicate that the transmission efficiency of the main channel is above 99%, the coupling efficiency of the sub-channel is above 96%, which also validates the reasonability of synthesizer design. At the same time, the prototype of synthesizer is designed and the HPM experiment system is established. The transmitting and coupling efficiency are both greater than 95% in cold test condition and they are also greater than 90% in gigawatt class test condition, the power capability of the synthesizer reaches about 1.2GW. The test results validate the feasibility of synthesizer for gigawatt class HPM.
Geosynchronous (GEO) synthetic aperture radar (SAR) has an orbit height of 36 000 km which results in long round-trip time. Thus, the 'Stop-Go' assumption and the conventional slant range model for low-Earth-orbit (LEO) SAR lose effectiveness in GEO SAR. A concise signal propagation delay equation of GEO SAR is presented and furthermore an equivalent slant range model is proposed. To verify the accuracy of the proposed model, the dichotomy method is applied to obtain the real slant range. In addition, the effects of the 'Stop-Go' assumption on GEO SAR are analysed by theoretical analysis. Promising results were obtained by several experiments.Introduction: The concept of geosynchronous (GEO) synthetic aperture radar (SAR) was first put forward to overcome the disadvantages of the long revisit cycle and limited swath coverage in low-Earth-orbit (LEO) SAR by Tomiyasu and Pacelli [1]. Although this concept provides significant advantages, it brings a lot of technology challenges. Owing to the increase of orbit height and the effects of earth rotation, GEO SAR has a long round-trip time and complicated relative motion trajectory, resulting in the conventional 'Stop-Go' assumption and slant range model for LEO SAR losing effectiveness in GEO SAR. Tian and Yu [2] considered the error brought about by the 'Stop-Go' assumption and gave an accurate slant range model of GEO SAR, but it is based on the circle orbit and not an analytical solution. Although Hu et al. [3] gave the error caused by 'Stop-Go' assumption and derived a new frequency-domain focusing method, the accuracy of the range model is not verified by the real slant range and the lack of theoretical analysis with the 'Stop-Go' assumption. This Letter derives a concise signal propagation delay equation of GEO SAR and gives an equivalent slant range model. Then, the dichotomy method is applied to obtain the real slant range. In addition, the error of the 'Stop-Go' assumption is analysed by theoretical analysis. The proposed approach is verified to be feasible through computer simulation.
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