具可調傳輸零點之高方向性微帶耦合器

Abstract

本論文提出一個具有高方向性及可調傳輸零點的微帶方向耦合器之設計，電路由二段四分之一波長平行耦合線及一段四分之一波長耦合的三階傳輸線濾波器組成，在中心頻率可產生一隔離零點以改善耦合器的方向性，且在耦合端埠可產生一對零點；藉由改變濾波器短路殘段的阻抗，可以控制此對傳輸零點。本文利用鋸齒耦合線結構使奇模和偶模的傳播相位速度一致，明顯改善了上止帶的抑制效果。本文中共有五個電路實作，並加以量測以驗證所提出設計，量測結果與模擬相當一致。

This thesis presents design of a high directivity coupled microstrip directional coupler with tuneable transmission zeros. The circuit consists of two quarter-wavelengh parallel-coupled-lines and a third-order bandpass filter. An isolation zero is devised to improve the directivity of the coupler at the center frequency. In addition, a pair of tuneable transmission zeros are created at the coupled port. The control of these two transmission zeros is achieved by adjusting the line impedance of the short-circuited stubs of the filter.Corrugated microstrip coupled-lines are synthesized to equalize the phase velocities of the odd and even modes. It can significantly improve the rejection of the microstrip coupler in the upper stopband. Five circuits are fabricated and measured to verify the idea. Measurement and simulation results show good agreement.