Broadband Omnidirectional Antennas And Electromagnetic Analysis Of Radomes

The dependence of modern war on the secure and high quality information puts forwardmore and more requirements to the antenna, which is the key component of the wirelesscommunication and weapons. On the one hand, frequency-hopping and spread-spectrumtechniques require the antenna must be broadband. On the other hand, to ensure the stabilityand reliability of the antenna in the natural and martial circumstance, the radome becomesnecessary in the antenna system. The accurate analysis and design of these electromagneticsystems is an urgent and important issue. Being associated with two research projects, thisdissertation makes deeply insight to the broadband wire antennas on the finite conductingground and the antenna/radome system. The author's major contributions are as follows:1. A new moment method is presented to analyze sleeve monopole antennas at the center ofa circular ground plane. Firstly, by adopting the efficient and accurate modeling of moderatelythick cylindrical wire antennas, the current distribution density on the antenna and the groundplane can be calculated when the moment method is used to solve them together, where thesinusoidal-interpolation basis function is utilized. Secondly, The variation of the inputimpedance and radiation pattern of the antenna with the size of the ground plane isinvestigated.2. The broadband wire antennas attached to arbitrary conducting ground plane are studied.Firstly, the broadband wire antenna can be described as surfaces, wires and wire/surfacejunctions from the structure. The basis function presented by RWG is used to present thecurrent on the surfaces. The triangular basis function is used to present the current on thewires, and a special basis function is used to present the current on the wire/surface junctions.Secondly, techniques are used to ensure the current continuity at the junctions ofmulti-segments or multi-patches and the accuracy of feeding on the patch, which makes themethod more universal in analyzing the broadband wire antennas attached to arbitrary groundplane. Lastly, the conical antennas and sleeve antennas on arbitrary ground plane are analyzedrespectively.3. A fast algorithm based on the integral equation is studied. To overcome the drawbacks ofthe moment method in memory and computation operations, adaptive integral method (AIM)is deeply investigated. The theory, application, memory requirement and operations arestudied based on the volume integral equation (VIE). A moment method solution based on theVIE suitable for arbitrary dielectric objects is obtained, and the application of the AIM notonly saves the memory but also improves the computation speed of the moment method.4. The electromagnetic properties of the antenna in the presence of the radome are studied.The application of the adaptive integral equation based on the volume integral equation isextended to the radiation field from scattering problem, which makes the radiation propertiesof the antenna in the presence of the arbitrary radome can be accurately calculated. Then,some antenna/radome systems are studied using this method.5. A new moment method is presented to accurately analyze the coupled conducting anddielectric targets. Firstly, by adopting volume integral equation for the dielectric target andsurface integral equation for the conducting target, the coupled volume-surface integralequation is obtained. Secondly, an effective pre-conditioner for the method of moments(MoM) solution to the coupled volume-surface integral equation is presented to calculateelectromagnetic scattering from conducting and dielectric targets. In comparison with otherpre-conditioners usually used (incomplete LU factorization technology, ILUT), there are threemain advantages of the pre-conditioner in this paper: A). Our method doesn't need additionalcomputer memory, and it only needs fewer CPU time. While in the ILUT method one mustintroduce an additional array to store the array decomposed, resulting in the restrictionproblem in the computer memory. B) If the storage is available, one can further combine theother pre-conditioner (ILUT) with our method, and the convergence properties will also bebetter than the ILUT used only. C) Our method is easier to combine with the fast algorithms.6. Adaptive integral method (AIM) is combined with the moment method based on thecoupled volume-surface integral equation. The application of AIM significantly reduces theCPU time and computer memory, which makes the method feasible to analyze the electricallylarge conducting/dielectric targets, for example, the radiation characteristics of the antenna inthe presence of the radome.