الفهرس 
Helical AntennasOnly 14 pages are availabe for public view
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Abstract
The simplicity and reduced cost of wire antennas made them good winners in the field of telecommunications. They are used in various applications in both the transmitting and receiving modes. Although, they are characterized by their flexibility of operation in the UHF, VHF, MF and LF frequency ranges, they have low gain values. The majority of previous work on helical antennas had been focused on uniform diameters, inspite of presence of other parameters whose variation effect can achieve an optimum gain.
In this thesis, analysis and design methods are applied by using the NEC commercial code based on the methods of moments, which is obviously discussed in the second chapter.
Variations of the helix diameters and profiles are considered in chapter three to get the uniform, linear, logarithmic and exponential helices. The study of the ground effect is applied also on each profile, but in the case of no ground effect we conclude that the exponential helix gives the better performance. When adding a ground, the linear helix gives gain of20 dB, which is better than 17 dB that resulted by exponential helix without applying ground.
The next step is changing the feeding of the helix by varying the pitch and noticing its effect on the radiation characteristics as shown in chapter four. Also the helices of uniform and non-uniform profiles are loaded at different positions by different values of resistance and inductances. In this case, the current distribution is computed and the electric field in the vertical plane and the gain are investigated. Finally we search for a profile gives better characteristics by changing the pitch angle a of the exponential helix and studying the resulting effect on the antenna characteristics.