Design Of An Omni High Gain Antenna And Analysis Of The Influence Of Buildings And Ground On The Short-wave Antenna

Currently, communication systems increasingly require better services for users, and the electromagnetic environment of antennas becomes more and more complicated with the development of urban infrastructure. Therefore, the design for high gain antennas and the surroundings' influences on antenna cause great interest. This paper studies antennas in two aspects based on theoretical analysis and the Finite Difference Time Domain (FDTD) method. First, an omni high gain antenna is designed and optimized; Second, the influences of high buildings and ground on short wave antennas are analyzed with the simulation of the FDTD method.To design omni high gain antennas, the paper studies the structures and principles of omni communication antennas. For the coaxial collinear antenna, the paper analyzes the distribution of its electric field and analyzes the main factors on affecting the antenna according to the results of simulation. Some methods are taken to improve the gain of the antenna, such as calculating the length of elements, adjusting the distance among them, and modifying the structure of the antenna. These methods ensure the same phase and amplitude of the current on all elements. To improve the antenna's efficiency, a special structure was employed. Both ends of each element are filled with Teflon while the middle of each element is vacant in order to decrease the dielectric loss. The coaxial collinear antenna is easy to get a good feeding and matching in a wide band frequency. Finally, with the FDTD method and the FEM (Finite Element Method), we simulate the antenna. The resultsshow that the gain increases 2.5dBi in the range of 14dBi-15dBi compared with the original antenna. The antenna's bandwidth extended from 5.6GHz to 5.85GHz, which is as twice as some products'. The parameters of the antenna satisfy the design requirement.At the same time, this paper studies the influence of high buildings and ground with different conductivities on short-wave antennas. First, the condition to consider the ground as a conductor is discussed. Then, the fishbone antenna as the example of a short-wave antenna is analyzed. The simulation model of the fishbone antenna, high buildings and different grounds is constructed. In the simulation, the modeling method of thin wires and surface impedance boundary condition are introduced. The FDTD method is used to calculate the far fields of the fishbone antenna. Finally, the influence of high buildings and grounds with different conductivities on the pattern is analyzed and discussed. The results have a good agreement with the results obtained by commercial software and theoretical analysis as referred.