以平行三微帶線結構設計寬頻帶通濾波器及其二階諧波的抑制

Abstract

本文以平行三線微帶結構設計寬頻帶通濾波器，主要關鍵是建立平行三線微帶單節電路參數和單個導納轉換子的關係。論文中提供了介質常數2.2的設計圖，且實際製作兩個二階，通帶中漣波為1dB和比例頻寬分別為40% 和60% 的柴比雪夫濾波器，模擬和實際量測的結果相當一致。 為了抑制平行三微帶線寬頻帶通濾波器的二階諧波，我們使用了鋸齒型微帶線。主要是使兩個實際的激發模在傳播方向的相速相等，量測的結果說明，以這種結構所設計的寬頻濾波器，其二階諧波可以抑制在-50dB以下。

Bandpass filters are designed based on parallel coupled three-line microstrip structure. The relation between the circuit parameters of a three-line coupled microstrip section and an admittance inverter is established. A design graph for substrate with Er=2.2 is provided. Two Chebyshev filters, of order 2 and 1dB passband ripple, with fractional bandwidth 40% and 60% are fabricated and measrued. Good agreement between prediction and measurement is obtained. Line corrugation is introduced to the three-line microstrip wideband bandpass filters for suppressing the spurious response at the second harmonic (2fo). The corrugation is used to equalize the phase velocities in the propagation direction of the two activated eigen-modes. Measured results show that a suppression better than –50dB can be achieved.