Investigation of Propagation Characteristics and Energy Leakage of Guided Waves in Open Planar Transmission Lines and Their Applications

• Main Authors: Sheen, Jyh-Wen, 沈志文
• Other Authors: Yu-De Lin
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/24046063981920229817

博士 === 國立交通大學 === 電信工程研究所 === 84 === The leaky-wave-related propagation properties and their applications in openplanar transmission lines are investigated in this thesis. In part I of thethesis, the analyses of the surface-wave-leakage-related propagationcharacteristics in open planar transimissiom lines are included. Threecommonly encountered moding problems in open planar transmission lines are allpresent in the coplanar strips (CPS) cases. First, in the lower frequencyregime, there is an extra surface-wave-like mode exsiting. Respective fieldand current distributions of the dominant CPS mode and the surface-wave-likemode are presented since this surface-wave-like mode may be inadvertentlyexcited. This surface-wave-like mode is also essential in explaining the modeevolution around the spectral gap frequency regime when the bound CPS modeevolved into a leaky complex mode. Second, after the onset of leakage intothe surface wave of the supporting structure, the normalized leakage constantof the leaky CPS mode exhibits a sharp an deep minimum as witnessed in thecoplanar waveguide (CPW) case. Third, as the strip width of the CPS isincreased beyond certain values, both the leaky mode and the bound mode canexist simultaneosly in the full higher frequency regime. Also, the effect ofthe nearby back conductor plane on the surface wave leakage of the CPS and CPWcircuits is investigated for the design of appropriate supporting structures.The variation of mode evolution patterns between the CPS and the conductorbacked coplanar strips (CBCPS) are presented. How the back conductor planesinfluence the frequency point associated to the surface wave leakage of CPWis discussed. Moreover, the common features of the surface-wave-like modeparasitizing in most supporting structures are described by an example of thesurface-wave-like mode in slotline. The conditions of the existence of thesesurface-wave-like modes are explained. In part II of the thesis, the space--wave-leakage propagation characteristics and their applications are included. Fisrt, an analytical method for theoretical verification and analysis of themode nature of the microstripline first higher order mode is proposed. Theradiation efficiency of the microstrip line first higher order mode as aplanar leaky-wave line source is also investigated. The spectral domainapproach is used to calculate complex power flows propagating toward differentdirections. By observing the complex power flows, the mode nature in differentfrequency regimes can be clearly distiguished. Also, the amount of powercarried by the surface wave leakage and that by the space wave radiation canbe separated by choosing the integration paths appropriately in the spectraldomain. By comparing the amounts of these two types of power excited by themicrostrip line first higher order mode, it is found that the microstrip lineis more efficient as a leaky- wave line source when its substrate is thin, thedielectric constant of the substrate is low and the antenna main beam is awayfrom the endfire direction. Second, after the analyses of the mode nature ofthe microstrip line first higher order mode, the efficient excitation methodsof this planar leaky-wave line source are investigated. Three arrangements ofthe feeding structure for the excitation of a microstrip leaky wave antennaare proposed. And a full-wave spectral domain integral equation methodcombined with the fundamental mode sampling technique is applied to determinethe reflection coefficient of the excitation source. Tabulation technique isused to reduce the computational effort. Dependence on structural parameterssuch as line width, line spacing and overlap length is fully analyzed toobtain the design criteria for a microstrip leaky wave antenna. Also, anexperimental setup is used to check the validity of our numerical resultsand verify the radiation nature of the microstrip line first higher ordermode. Additionally, a modified dynamic model in integral equation methods forcharaterizing the discontinuities problems is proposed to improve thecalculation efficiency. Third, a new uniplanar leaky wave line source forrealization of a uniplanar leaky wave antenna is investigated with thespectral domain approach. This line source comes from the first higher ordermode of slotline. The leakage constant and the radiation band of this firsthigher order mode is larger than that of the microstrip line first higherorder mode. The geometric dependences and the effect of finite conductorplanes are analyzed. The undesired dominant modes (surface-wave-like modes)in cases of slotline with finite and infinite conductor planes are alsodiscussed. Moreover, feeding structures are proposed for efficient excitationof the leaky wave line source Finally, experimental results show agreementwith our numerical results and further identify the existence of the slotlinefirst higher order mode and the possibility to implement an uniplanar leakywave antenna.