利用懸浮結構抑制微波帶通濾波器二階諧波之研究

Abstract

將耦合微帶線率波器的基板(Substrate)懸空可以抑制在二倍頻( )所產生的虛假響應(spurious response) 或二次諧波，我們使用全波頻域法(Full-wave spectral domain approach, SDA) 分析懸空的耦合微帶線，當基板懸空在特定某一個高度時，耦合微帶線的奇模跟偶模的相位速度，在二倍頻處完全相同，可以抑制二次諧波的假響應。本文設計並實作了三個不同規格的濾波器，為降低製作成本，在每一個濾波器中，每一個耦合段的懸空高度都是一致的，量測結果顯示，這些濾波器的二倍頻假響應都有很好的抑制效果。

The spurious response of microstrip bandpass filter at twice the passband frequency (2fo) is suppressed via substrate suspension. The suspended coupled microstrip lines are analyzed by the full-wave spectral-domain approach (SDA). It is found that for each coupled section in a suspended bandpass filter, a specific height of substrate suspension can be obtained to equalize the phase velocities of the even-mode and odd-mode, so that the spurious response at 2fo can be completely suppressed. Three filters with uniform suspension height are designed and fabricated. The measured results show good rejection levels at 2fo.