Yes / In this paper two novel antennas, suitable for access and backhaul links, are designed, fabricated and tested for a Relay Station in a WiMAX wireless network. A single modi¯ed E-shaped patch antenna is described, presenting 10 dB gain over 12.4% bandwidth. This antenna element is used for the design of a 4 £ 4 planar array which provides experimental gain of 21.2 dB. The antenna system on the Relay Station operates at 3.4 GHz and includes one single antenna element for access link realization and an antenna array for the backhaul link realization. These antennas are installed in two con¯guration arrangements and tested in terms of their radiation performances and coupling e®ects. The simulated and measured results are quite satisfactory and in good agreement at which the maximum coupling between the access and backhaul antennas is found below ¡25 dB for all tested cases.

This thesis investigates the variations of electrical properties of linear antennas mounted on certain platforms, depending on the physical properties of that platform. In this respect, related basic antenna simulations, electromagnetic simulations from primitive to complex models of airframes, and scale model measurements were used. Firstly, electrical properties of monopoles at known environment were examined and basic analyses were performed via an electromagnetic simulation tool, named CST Microwave Studio&reg / . In addition, important aspects of simulation tool were investigated. Then, an F-4 aircraft model was used to observe the electrical characteristics of antennas mounted on it. Using 3D model of F-4 aircraft, realistic antenna placement points were assigned and monopoles were attached to those points. Alternatively, a simplified F-4 model was also used and for two different models, identical simulations were done, followed by accuracy and performance analysis between the results obtained from simplified and exact models. As the outcome of these simulations, certain parameters like impedance, antenna-to-antenna coupling and radiation pattern values were examined. Additionally, change in antennas&rsquo / electrical characteristics due to their position over the airframe was investigated. In addition, a 1:10 down-scaled and copper-plated F-4 aircraft model was obtained and equipped with identical antennas. By using the measurements done on this scale model, antenna-to-antenna coupling results of MWS&reg / were verified by measurements. Finally, advantages and disadvantages of using electromagnetic simulation tools and scale model measurements for such antenna studies were discussed.

With improvements in hardware of antenna receivers, fully digital arrays have been made possible to use in real time systems. These systems have a greater complexity, with the advantage of more dynamic system design since the use of the communication system can be changed with only a software change. Construction of a system capable of bidirectional communication on the same frequency and at the same time, is possible with a fully digital array if the coupling between the antenna elements are known. The good thing about the system is that all components for measuring this coupling already are included in the fully digital array. A signal generator and a coherent multichannel receiver can be used to create a VNA, completely by software. This can be used to measures the coupling coefficients of the antenna elements. In this thesis the working principle of the the software defined VNA is proven, a testing environment for a antenna array is described andadjustments for real hardware are used to create a result which can be strongly correlated to measurements of a lab grade VNA used as reference.

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