本文選題：低頻地波　切入點：時域有限差分方法　出處：《西安理工大學(xué)》2017年碩士論文

【摘要】：低頻地波信號因其傳輸穩(wěn)定、衰減小、繞射能力強、傳播距離遠(yuǎn)等特點而被廣泛應(yīng)用于遠(yuǎn)距離導(dǎo)航、授時和通信等方面。然而,受到傳播路徑地形起伏變化、地物非均勻分布、大氣環(huán)境空時變化等因素的影響,使得實際低頻地波信號的傳播速度、方向和相位等有別于真空中的情況。研究復(fù)雜環(huán)境下低頻地波傳播特性的高精度快速預(yù)測方法是提高低頻地波導(dǎo)航授時系統(tǒng)精度的關(guān)鍵。現(xiàn)有的時域有限差分方法(Finite-Difference Time-Domain Method,FDTD)能夠模擬實際信號的傳播過程,但長距離應(yīng)用時存在數(shù)值色散誤差大、計算機(jī)消耗過大等問題;時域偽譜方法(Pseudo-spectral Time-Domain Method,PSTD)能夠處理電大尺寸電磁計算問題,但對復(fù)雜結(jié)構(gòu)及媒質(zhì)突變問題處理困難。針對上述問題,本文提出一種“FDTD+PSTD”頻域空域結(jié)合的數(shù)值預(yù)測方法,通過將傳播區(qū)域進(jìn)行劃分,結(jié)合FDTD方法與PSTD方法各自優(yōu)勢,實現(xiàn)低頻地波傳播性能的高精度、快速預(yù)測。具體研究內(nèi)容包括:首先,從FDTD和PSTD的基本理論出發(fā),推導(dǎo)了兩種算法的實現(xiàn)過程并進(jìn)行了仿真驗證,對比分析了各算法的特點;其次,針對低頻地波傳播問題,分析了 FDTD方法與PSTD方法應(yīng)用于該問題的可行性與存在的問題;再次,基于上述分析結(jié)果,提出“FDTD+PSTD”頻域空域結(jié)合的數(shù)值預(yù)測方法,從區(qū)域劃分、結(jié)合模式、場量迭代方式、網(wǎng)格剖分、分界面處場量傳遞等方面進(jìn)行系統(tǒng)研究,仿真驗證了不同地面模型下混合算法的有效性;最后,將混合方法進(jìn)一步應(yīng)用于天線近場效應(yīng)研究,仿真分析了地面條件對天線輻射特性的影響。仿真結(jié)果表明:在保證一定的預(yù)測精度下,計算相同區(qū)域時混合算法比FDTD在計算速度上快3～4倍,而在內(nèi)存占用上則少1～2倍;同時,近場區(qū)地面條件對天線的輻射特性及相位中心將產(chǎn)生較大的影響。本文研究成果將為長距離、大面積低頻地波傳播性能的高精度預(yù)測及其工程實現(xiàn)提供技術(shù)支撐。
[Abstract]:Low frequency ground wave signal is widely used in long range navigation, timing and communication because of its characteristics of stable transmission, low attenuation, strong diffraction ability and long propagation distance.However, due to the influence of the topographic fluctuation of the propagation path, the uneven distribution of ground objects and the space-time variation of the atmospheric environment, the propagation speed, direction and phase of the actual low-frequency ground wave signal are different from those in the vacuum.It is the key to improve the accuracy of low-frequency ground-wave navigation and timing system to study the high-precision and fast prediction method of low-frequency ground wave propagation in complex environment.The existing Finite-Difference Time-Domain method (FDTD) can simulate the actual signal propagation process, but the numerical dispersion error is large and the computer consumption is too large.Pseudo-spectral Time-Domain method (PSTD) can deal with electrically large size electromagnetic computation problems, but it is difficult to deal with the problem of complex structure and medium mutation.In order to solve the above problems, this paper presents a numerical prediction method combining "FDTD PSTD" in frequency domain. By dividing the propagation region and combining the advantages of FDTD method and PSTD method, the high precision and fast prediction of low-frequency ground wave propagation performance can be realized.The specific research contents are as follows: firstly, from the basic theory of FDTD and PSTD, the realization process of the two algorithms is deduced and verified by simulation, and the characteristics of each algorithm are compared and analyzed. Secondly, aiming at the problem of low-frequency ground wave propagation,The feasibility and existing problems of applying FDTD method and PSTD method to this problem are analyzed. Thirdly, based on the above analysis results, a numerical prediction method combining "FDTD PSTD" in frequency domain is proposed, which can be divided into regions and combined modes.The simulation results show that the hybrid algorithm is effective under different ground models. Finally, the hybrid method is applied to the near field effect of antenna.The effects of ground conditions on antenna radiation characteristics are simulated and analyzed.The simulation results show that the hybrid algorithm is 3 ~ 4 times faster than FDTD in computing the same area and 1 / 2 times less in memory than FDTD under certain prediction accuracy.The near field ground condition will have a great influence on the radiation characteristics and phase center of the antenna.The research results in this paper will provide technical support for the high precision prediction and engineering realization of the low frequency ground wave propagation performance in long distance and large area.
【學(xué)位授予單位】：西安理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN011

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