Research On Artificially Soft And Hard Surfaces Structures In Electromagnetics And Their Applications

Soft and hard surface behave as a mixture of simultaneous PEC and PMC properties. Generally, the hard surface will support waves with a maximum value of the E-field at the surface for any polarization, whereas the soft surfaces makes the amplitude of the E-field zero at the surface. Due to the specific electromagnetic properties of artificial electromagnetic soft and hard surfaces, they have a wide range of engineering applications in the field of microwave and antenna.Previous studies of electromagnetic soft and hard surfaces focused on the ideal boundary conditions and numerical analysis, and the design and application of artificial electromagnetic soft and hard surfaces has just begun. Therefore, the design and application of miniaturized soft and hard surfaces which have broadband bandwith urgent need to be studied. In this thesis, we mainly study the basically theory and design methods of soft and hard surface, electromagnetic soft surface and its application to reduction of mutual coupling between antennas, and invisibility cloak of metal cylinder which is based on the electromagnetic hard surface structure. The main work and contributions in this thesis are outlined as follows:1. Electromagnetic properties of electromagnetic soft surface and the effects of all structure parameters on band-gap are analyzed. The impact of distance of inter-cycle unit has been mainly studied, and based on these, the design of new artificial soft surface structure is guided.2. A miniaturized wideband electromagnetic soft surface structure is proposed. The miniaturized soft surface structure is achieved by making slots on the strips of the soft surface, and the wideband effect is achieved by using metallic strips with ledge edges. Compared with the soft surface structure proposed by Said A.Abushamleh, when the electromagnetic soft surface unit is 8 mm, the center frequency is changed from 6 GHz to 5 GHz, and the relative bandwidth increase from 8.1% to 12.5%. And when the soft surface structure is applied to reduce coupling between microstrip antennas, coupling reduction of the relative bandwidth increase from 2% to 8%.3. Electromagnetic properties of the strip type electromagnetic hard surface and the effects of all structure parameters on bandwidth are analyzed. The scattering properties of the hard surface are mainly discussed, and when the plane of the incident wave is paralleled to the strips and for TE polarization, the hard surface has almost omnidirectional RCS reduction.4. A design method of invisibility cloak for metal cylinder is proposed. Compared with other design methods of electromagnetic invisibility cloak, it is simple and easy to apply. And compared with the design methods of hard surface cloak proposed by Kildal, this hard surface has wider bandwidth and can be made thinner, for example, when the center frequency is at 4.2 GHz, the bandwidth increase frome 14.3% to 22.2% and the thickness decrease from 9.41 mm to 2 mm.