Characteristics and Design of Broadside-Coupled Transmission Lines at Higher-Order
|關鍵字:||寬邊耦合;高階;洩漏模;天線陣列;高增益;窄波束;八木;多層;broadside-coupled;higher-order;leaky mode;array antenna;high-gain;narrow-beam;Yagi-Uda;multilayered|
The aim of this work is two fold, 1) detailed description of the higher-order leaky modes of the much used broadside-coupled microstrips and 2) practical application of such leaky modes as an antenna. A representative broadside-coupled transmission line structure is examined to elucidate the detail of leakage effects at higher-order of multilayered, 3-D microwave and millimeter-wave circuits. Two-layered cases are analyzed from a physical perspective and the total number of first higher-order leaky modes is found to be equal to that of microstrips. The higher-order leakage effects of general multilayered broadside-coupled transmission lines are thoroughly investigated via the studies of the cases of three to five-layered broadside-coupled microstrips. Several significant conclusions can be derived from the details of the dispersion characteristics and modal current distributions of the higher-order leaky modes exist in the broadside-coupled microstrips. With the aim of the results found in this thesis, one can sophisticatedly control the coupled leaky modes to avoid adverse effects, or apply these modes in high-gain antenna application. One of the two first higher-order leaky modes obtained in the two-layered case is weakly attenuated, while the other is strongly attenuated. A high-gain, narrow-beam leaky-mode antenna using only the weakly attenuated leaky mode is designed and measured as an application of this broadside-coupled structure, exhibiting a marked beam-width reduction of 60%. This antenna is the first Yagi-Uda-like array antenna that utilizes the higher-order leaky modes of the microstrip, for which the three basic elements - driver, reflector and director - are stacked in the broadside direction. The attenuation rate can be further reduced by adjusting the strip width of the director. The half-power beam-width of the leaky-mode antenna applying two-layered broadside-coupled microstrips with wider top microstrip is measured to be 2.1o at 25.2o from the broadside at 34 GHz. A one-dimensional leaky-mode antenna is successfully designed and measured. This antenna array needs simpler feeding network to realize a nearly-broadside pencil beam radiation and shows high efficiency and performance.
|Appears in Collections:||Thesis|