Design and Implementation of Mobile Base Station Antennas.

Abstract

Mobile base station system represents one of the important systems in communication networks. This is due to the fact that it is responsible for setting up a wireless routing path between the mobile handset/mobile stations (MS) themselves. These hand held devices are considered one of the important things in our daily life. In modern mobile base stations communication systems, the mobile operators always require much broader bandwidths or need additional operating frequencies to cope the rapid development of mobile communication systems and the capacity problems in the conventional mobile base station transceiver system such as 2G system (i.e. GSM900 band). Based on this fact, much work has been devoted to increase the bandwidth or to obtain dual frequency characteristics of the microstrip antennas. Additional licenses or bands such as DCS1800 (Digital Cellular System) in 2G, PCS1900 (Personal Communications Service) in 2G, UMTS2100 (Universal Mobile Telecommunication System) in 3G and several bands of LTE (Long Term Evolution) in 4G are used to overcome these problems. Not only adding new bands in the same generation or even upgrading to new generation of the mobile network overcome the capacity problems in the mobile network but also introduce a perfect service by increasing the assigned data rate for each channel compared to the preceding generation. Our proposed work in this thesis is to design and implement a mobile base station linear microstrip antenna array, feeding network used to excite the linear antenna array and a microstrip duplexer. Our implemented mobile base station antenna is designed to be used in 2G, 3G and 4G of the mobile networks. This mobile base station antenna supports the mobile operating bands such as GSM850, GSM900, DCS1800, PCS1900, UMTS2100, and their equivalent bands in CDMA and LTE bands. In order to design and implement the mobile base station antenna, it is important to assign the required electrical specifications of the mobile base station systems. These specifications include the operating frequency bands, the gain, the vertical half power beamwidth (V-HPBW), the horizontal half power beamwidth (H-HPBW), the front-to-back ratio (FBR), the polarization diversity, the isolation between ports and side lobe level (SLL). Depending on these specifications, the mobile base station designers enable to assign the best type of single antenna element, the maximum number of antenna elements that are located vertically in linear array, the excitation coefficients used to feed the linear antenna array. Also, the proposed linear antenna array is designed to operate in both transmitting and receiving sides due to the use of two orthogonal feed lines used in the same antenna. A high isolation between the transmitting and the receiving ports is introduced. Four different antenna elements are proposed. Three antennas are designed on FR4 substrate material while the fourth antenna is designed on Rogers RT/Duroid 5880. Three antenna elements have dual linear polarizations so, they are used as transceiver antennas (transmitting and receiving) while the fourth antenna design has a single polarization plane so, it is used only as a transmitting or receiving antenna. A comparative study is performed between the use of the method of moments (MoM) in conjunction with the genetic algorithm (GA) once and the ant colony algorithm (ACO) another time. The hybrid algorithms are used to calculate the excitation coefficients and the optimum separations between the elements of the antenna arrays. Based on the proposed aforementioned excitation coefficients, two feeding network circuits are proposed to excite two linear antenna arrays. All these feeding network circuits are designed and fabricated on FR4 substrate material.