地波雷達的在實際應用上，由於部署的位置大部分在沿海，造成在激發地波前電磁波會經過一個過渡的地帶，例如沙灘、沙地等，激發與地波模態不匹配的介質平板波導模態，進而產生洩漏天波，針對這樣的議題本論文設計了伸縮週期性結構，伸縮週期性結構由金屬條陣列與基板所組成，透過人工調整金屬條之間的間距，使伸縮週期性結構所支撐的類表面電漿模態電場分布與地波相似，將其放置於地波雷達天線與海水之間可以作為一模態過渡的結構，在不同頻段產生與地波匹配的電場分布，幫助地波雷達天線輻射能量耦合成地波進而提高激發地波的效率，一方面可以解決模態不匹配的議題，另一方面由於能量守恆定理，地波雷達天線激發天波的比例就會減少，天波干擾的情況也會減少。 本論文第二章解釋如何讓伸縮週期性結構達到人工可調的目的，並透過本徵模(Eigenmode)分析驗證吾人的伸縮週期性結構可以支撐類表面電漿模態，並且在金屬條間距不同時，會有不同的類表面電漿模態的色散關係，因此在同樣的頻率下可以有不同的電場分布。 本論文第三章在微波頻段透過量測結果驗證，伸縮週期性結構藉由人工改變金屬條的間距，確實可以在量測的頻段(0.7GHz-3GHz)中達到地波增強的效果，並且具有85%的相對頻寬，可以實際應用於地波雷達中。 ;A ground wave radar is most commonly deployed along coastal areas. This causes the electromagnetic wave to pass through a transition zone, such as sandy beach, before the excitation of the ground wave. In this case, a dielectric slab waveguide mode that does not match the ground wave mode will be excited. Therefore leakage sky waves are then generated. As mentioned above, tunable guided-wave structure is designed in this paper , A tunable guided-wave structure consists of a metal strip array and a substrate. By manually adjusting the spacing between metal strip, the Spoof Surface Plasmon mode field distribution supported by the tunable guided-wave structure is similar to that of ground waves. It is possible to transition from one mode to another between the antenna and the seawater by using tunable guided-wave structures Match the field distribution of ground waves in different frequency bands in order to enhance the efficiency of ground wave excitation by coupling the radiant energy of the ground wave radar antennas into the ground waves. On the one hand, it can solve the problem of mode mismatch, and on the other hand, due to the law of conservation of energy, the proportion of sky wave excitation by ground wave radar antenna will be reduced, and the sky wave interference will be reduced.
Chapter 2 explains how to make the tunable guided-wave structure manually tunable. The eigenmode analysis verifies that our tunable guided-wave structure can support Spoof Surface Plasmon modes. When the spacing between metal strips is different, there will be different dispersion relations of Spoof Surface Plasmon modes, so there can be different electric field distribution at the same frequency. Chapter 3 of verifies the results of the transmission measurements in the microwave band. The tunable guided-wave structure can really achieve the effect of ground wave enhancement in the measured frequency band (0.7GHz-3GHz) by manually changing the spacing of the metal bars and has 85% relative bandwidth. it can actually be used for ground wave radar.
