الفهرس 
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Abstract
In recent years, research studies on the subject of metamaterials (MTMs) have increased immensely. The effect of metamaterials can therefore be tremendous if one can manipulate the wave properties, such as the significant decreases in the size of components. The objective of this thesis is to study the main properties of metamaterials for improving the performance of backward directional coupler. A compact structure of the backward directional coupler is proposed.
In this thesis we study in detail the performance of two different types of structures of microstrip coupled line couplers, Epsilon Negative Transmission line (ENG) coupler and coupled line coupler with tight coupling. The two structured are simulated using two main field simulators (HFSS, CST) and one circuit simulator (ADS).
The proposed unit cell planar type of composite right/left-handed (CRLH) metamaterial using microstrip technology with coupled lines and stub inductors is introduced. This structure has the main advantage of compact dimensions and easiness for design. The proposed unit cell can be designed in several frequency bands based on its geometrical parameters. The transition from LH to RH shows the balanced condition without the presence of stop band. Two designs for two different frequency bands have been carried out. The frequency band of the first design is about 320 MHz and the band of the second design is about 1.3 GHz. This unit cell is fabricated and its measurement results are shown. Good agreement has been achieved between the theoretical and the experimental results.
The backward directional coupler was designed based on the CRLH unit cell, it has a compact size (2.41𝑐𝑚2) with high coupling value (-1.5 dB) and compared with the conventional backward microstrip coupler. Instead of the normal conductor (Copper) used in strip line, it is replaced with a YBCO thin film high temperature superconductor (HTS) to achieve superior performance. A high directivity of the coupled line was achieved by using superconductor. The CST full wave EM simulator has been used to simulate this proposed backward directional coupler.