الفهرس 
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Abstract
In this work, a design procedure for designing wide band (both the input impedance bandwidth and the far field pattern bandwidth) electrically small to mid-size antennas using the theory of characteristic Modes (CM) and the theory of matching networks was presented. Another important goal of this work was the study of the behavior of the antenna input impedance as a function of the antenna’s number of feeds and their locations. A new model for antenna input impedance based on the theory of characteristic Modes was presented. The development of this model was a key contribution to this dissertation as it contributes to the understanding of the resonance phenomena of the input impedance of antennas. This model was extensively used in the preceding chapters to design wideband small to mid-size antennas. The model helped in showing that parallel resonance phenomena do not correspond to a single characteristic Mode but are rather due to an interaction of at least two nearby modes each having eigenvalues of opposite sign. This is in contrast to the series resonance phenomenon, which is mainly due to a single CM. A discussion of the rectangular microstrip patch antenna cavity modes and how these modes are related to CM was also discussed. It was concluded that the CM of the microstrip patch antenna does not correspond to its cavity modes. A Vee-shaped vertically polarized antenna was designed such that mainly one dominant mode is excited in the desired frequency band. High-order modes can be suppressed in the desired frequency band by a proper design of the feeding network. Two feeds were used to excite the proper mode of the Vee-shaped antenna to obtain vertical polarization; the right locations of the two feeds were chosen based on the knowledge of the antenna’s CM. Furthermore, a design technique applicable to both reconfigurable and wideband antennas that are based on the application of reactive loading was also presented. Passive loads were used in the design of a reconfigurable dipole antenna while non-foster reactive loads were used in the design of a wideband dipole antenna; the load values were calculated such that they resonate the antenna with one dominant current mode at different single frequency points (reconfigurable antenna) or over the whole frequency band (wide band antenna). The technique is applicable to small to mid-size antennas where high-order current modes are not strongly excited.
5.2 Future Work
• Apply the theory of CM to control the parallel resonance frequency point(s) of patch antennas mostly by loading it or by geometry modifications.
• Fabricate pattern reconfigurable antenna based on the theory of CM.
• Fabricate and build antennas using NIC (Negative Impedance Converters) to use them as loads for designing wideband electrically small antennas.
• Apply more than two feeds for the antenna conformal to Manta UAV to extend the antenna bandwidth.
As in microstrip antenna design, the antenna parameters are directly related to the dielectric characteristics and thickness of the substrate material used. Therefore, in the future other substrate materials could be used to improve the results. from our research study on the microstrip antenna design using defected structures, there is still an open field for more innovations, whether reducing the size of the antenna or enhancing its performance. Reducing the size can be made by using materials of high dielectric constants or by using other different shapes of defected structures.
Suggested future work can be accomplished in the following points:
• Establish performance evaluation procedure for microstrip antenna with DGS, and defected microstrip structure (DMS) based on CMA in electromagnetic simulator software and compare different antenna schemes
• According to the reciprocity theorem, we can simply look at the transmitting antenna in an early simulation
• Important parameters of the transmitting antenna: ΓdB, input impedance, radiation pattern, etc.
• After a thorough investigation by simulation, build the antenna on PCB and experiment with its practicability
• Investigate the equivalent circuit model.
• To study the effect of different structures of DGS on the microstrip antenna characteristics.
• To study the effect of defected structures on a different type of microstrip antennas like slots or patches.
• Reducing the microstrip antenna size and enhancing the performance can be achieved by understanding the current distribution of CMA configurations and structures.
• Further study is also needed for microstrip antenna with different feeding applied, such as coplanar waveguide (CPW). This is useful for future microstrip antenna design, to reduce the error due to misalignment between the microstrip line and DGS in the ground plane etched on both sides of the substrate during the fabrication process.
• Use characteristic mode analysis to mount new DGS and microstrip antennas at higher frequencies on more and more different boards. (CMA) To achieve better performance and integration capabilities with monolithic microwave integrated circuits (MMICs).
• Design and fabricate DGSs on microstrip antennas as a parasitic element which is still under investigation.
• Solve part of the actual measurement of the impedance mismatch problem. Measuring the actual field shape and gain.
• Simulate more multiband antennas accordingly with future wireless communication needs.
• Studying other antenna geometries: Different microstrip antenna geometries based on DGS and DMS.
• After convergence studies construct and test a multiband antenna.