Study Of Asymmetric Coplanar Waveguide And Its Bend Structure Based On Finite Difference Method

Coplanar waveguide, as a kind of important transmission line, has been implemented on microwave, millimeter wave, submilimeter wave, optics and high temperature superconducting integrated circuits, etc. even it has been applied in microwave circuits instead of microstrip, thus coplanar waveguide is occupying more important position in MMIC. The asymmetric coplanar waveguide is a novel transmission line developed from coplanar waveguide. Compared with coplanar waveguide, the slot widths of asymmetric coplanar waveguide are different, thus the asymmetric coplanar waveguide is a kind of extension of coplanar waveguide, and it has more generality and flexibility than coplanar waveguide.The asymmetric coplanar waveguide has been studied by many scholars, but the theory analysis and practical application are still at their stage of development for the limitation of the test condition and the application experience.In the theory analysis, asymmetric coplanar waveguide has been analyzed by many scholars using conformal mapping method, but the conformal mapping method can not be applied in frequency domain. Some scholars use the time domain methods, such as finite difference time domain method and multi-resolution time domain methods, to analyze the dispersion characteristics of the asymmetric coplanar waveguide, but the unique characteristics of the asymmetric coplanar waveguide cannot be found for the limited precision of these methods. This dissertation applies NPML boundary to2D finite difference frequency domain, then uses the new algorithm on the analysis of asymmetric coplanar waveguide. Compared with UPML finite difference frequency domain, NPML finite difference frequency domain is easy to implement by programming, and it is more suitable for open structure transmission line, such as microstrip line and asymmetric coplanar waveguide, etc. This dissertation has calculated the phase constant of the microstrip line, coplanar waveguide and asymmetric coplanar waveguide using2D finite difference frequency domain of NPML, and the asymmetric coplanar waveguide with via hole is analyzed for the first time through this algorithm. Because of the poor accuracy of finite difference frequency domain in the characteristic impedance calculation, the wave equation as interpolation function is added in the finite difference frequency domain to improve the accuracy of the algorithm.In the practical application, the study of discontinuous of asymmetric coplanar waveguide can not be overstepped. This dissertation mainly researches on asymmetric coplanar waveguide bend. First, the mode conversion of asymmetric coplanar waveguide is investigated through finite difference frequency domain and finite difference time domain. Second, through analyzing the mode conversion of three kinds of asymmetric coplanar waveguide and coplanar waveguide bends, it is noted that the energy conversion of asymmetric coplanar waveguide between modes is smaller compared with coplanar waveguide. That means the asymmetric coplanar waveguide bend can transmit signal better. Third, for verifying the low transmission loss of asymmetric coplanar waveguide, a new test fixing is proposed and designed by taking advantage of different field distribution of different modes. According to the characteristics of asymmetric coplanar waveguide, a novel coplanar waveguide is proposed by combining the transformation unit between asymmetric coplanar waveguide and coplanar waveguide. The experiment shows the novel coplanar waveguide bend restrain the energy conversion effectively, and it has low transmission loss.