應用於802.11a與數位直播衛星的雙頻低雜訊放大器與可調式鏡像拒斥帶通濾波器之設計

Abstract

本篇論文提出一個以微帶線來實現的雙頻低雜訊放大器，並設計一個具有多重可調式帶陷的帶通濾波器；低雜訊放大器可以同時滿足IEEE 802.11a (5.725-5.85GHz)與DBS (11.7-12.5GHz) 接收機的需求，而濾波器的目的在於具有夠低的插入損失，又能夠解決超外插降頻的雙頻鏡像訊號問題。本雙頻低雜訊放大器分別在以上兩個應用的操作頻率附近，可提供0.92dB與1.21dB的雜訊指數，並且同時在兩頻段內提供平均約24dB 的增益，改善後的輸入反射損失平均都在-10dB以下。帶陷濾波器使用步階阻抗共振器(SIR，Stepped Impedance Resonator)架構，並配合非對稱的交叉指狀(Inter-digital)耦合線，設計出一個具有三個可調式帶陷的帶通濾波器，帶陷的頻率位置可以透過改變開路殘段的長度來調整，濾波器在上述兩頻段的插入損失理想上可小於1dB，反射損失可達-15dB以下，並可提供高達32dB的鏡像拒斥的效果。

This thesis discussed a dual-band LNA realized in microstrip line circuits, and proposed a band pass filter with adjustable notches. LNA can simultaneously satisfy the demand of IEEE 802.11a (5.725-5.85GHz) and DBS (11.7-12.5GHz) receivers , in addition , the filter provides a lower insertion loss , but also resolves the problem of dual-band image signals in heterodyne down converters. The dual-band LNA possesses 0.92dB and 1.21dB of noise figure within the two operation bands, 24dB conversion gain in average, and an improved input return loss no more than -10dB. The notched filter structures in SIR (Stepped Impedance Resonator), which can produce three adjustable notches by using asymmetrical inter-digital coupled lines. The frequency of the notches can be adjusted by varying the length of the open stubs on inter-digital fingers. The filter ideally provides an insertion loss lower than 1dB, a practical return loss higher than 15dB, and the image rejection reaches 32dB.