标题: 開放式平面傳輸線之傳播特性與能量洩漏之研究及其應用
Investigation of Propagation Characteristics and Energy Leakage of Guided Waves in Open Planar Transmission Lines and Their Applications
作者: 沈志文
Sheen, Jyh-Wen
林育德
Yu-De Lin
電信工程研究所
关键字: 表面波漏;空間波漏;類表面波模;微帶線高次模;槽線高次模;漏波天線;surface wave leakage;space wave leakage;surface-wave-like mode;microstrip higher order mode;slotline higher order mode;leaky wave antenna
公开日期: 1995
摘要: 在本論文中,開放式平面傳輸線波漏現象及其相關的傳播特性與應用被加
以研究。論文第一部分包含了表面波漏及其相關傳播特性的分析,三種在
開放式平面傳輸線常遭遇之模態問題被發現皆存在於共平面帶狀線(
coplanar strips)中,首先在較低頻率範圍存在著類表面波模(surface-
wave-like mode),再則在較高頻率範圍存在著表面波洩漏(sur-face
wave leakage)的問題,這個衰減常數產生一個尖銳的極小值,且發生在
洩漏開始的頻率附近,就像在共平面波導所發現的現象。然後則是當共平
面帶狀線之金屬帶寬超過某一數值時在整個高頻率範圍會同時存在另外一
個會洩漏的主模(additional leaky domin-ant mode)。另外,共平面導
與共平面帶狀線的背面金屬板對傳播特性的影響在本論文中亦被加以研究
以便設計適當的電路支撐架構。最後,寄生在大部分支撐結構下的類表面
波模的本性,在本論中也以槽線(slot line)的類表面波模為例子加以描
述,並且這些類表面波模存在的條件也被加以解釋。在論文的第二部分包
含了空間波漏相關特性的研究及其應用。首先,本論文提出了一個解析的
方法去證明微帶線第一階高次模(first higher order mode)的本性及分
析它的放射效益(radiation efficiency)。根據複數的功率流向(complex
power flows),這個微帶線高階模的本性便可獲取,而藉由在頻域分析
法(spectral domain approach)中積分圍線(integration contours)的選
定,表面波漏與空間波漏的多寡可分別取得,使得微帶線高階模的放射效
益得以加以分析。接著在微帶線高階模的特性被掌握之後,我們對如何有
效激發這個高階模以便應用其為一漏波天線加以研究。三種有效饋送結構
在本論文中被提出,並且以頻域積分方程法加以研究並歸納出設計準則,
對於數值分析所得的結果,在論文中有一個實驗加以驗證,另外一個改良
的數值方法亦被提出以增進數值分析的效率,最後一個新的共平面式的漏
波線源(leaky wave line source)亦在本論文中被加以研究,這個新的漏
波線源是來自槽線的高階模(slotline higher order mode)。幾何相關性
以及有效金屬板對這一個新的高階模的影響亦被深入探討,然後三種有效
饋送結構也在本論文中被提出,這個新的高階模的存在性,以及一個共平
面式漏波天線的可行性亦經由實驗得以證實。
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.
URI: http://140.113.39.130/cdrfb3/record/nctu/#NT840435041
http://hdl.handle.net/11536/60795
显示于类别:Thesis