目前商用市場上可看到的產品主要應用以802.11與藍芽(Bluetooth)兩種為主，本文將介紹涵蓋此兩種應用頻帶(2.4-2.5GHz和5.15-5.85GHz)的雙頻濾波器。在文獻上，兩頻帶頻寬差異很大的濾波器設計存在三個主要的問題：兩個頻帶插入損耗(insertion loss, )通常過大(超過3dB)、阻抗匹配普遍不佳(僅-10dB左右)、與選擇(selectivity)的不佳。本論文將提出利用開路共振器設計之雙頻濾波器，以兩種不同形式的開路共振器：金屬微帶線開路共振器和接地面缺陷接地結構開路共振器，分別做成兩個利用共振器耦合之帶通濾波器，將兩個帶通濾波器並接，利用能量饋入方式，使帶通濾波器本身即擁有零點，選擇度能夠藉由調整零點來控制，無須再額外加電路來做抑制，將饋入線改為分支饋入，維持在寬頻仍能擁有-10dB以下的反射損耗。由於雙頻帶通濾波器以並聯結合，兩頻帶帶通濾波器在頻段和頻寬上，獨立調整性大，本文將提出兩個不同頻段雙頻帶通濾波器，除了常用規格 2.4/5.2 GHz，另外為一個1.5倍頻的雙頻帶通濾波器：1.55/2.4 GHz，使用的板材厚度為0.8 mm的FR4基板，實現2.4/5.2 GHz雙頻帶通濾波器之量測結果，以TRL校正，兩個頻帶的插入損耗值和反射損耗值在2.4 GHz為-1.725 dB及-10.11 dB，在5.5 GHz則分別為-1.364 dB及-24.24 dB，實現1.55/2.4 GHz雙頻帶通濾波器之量測結果，以TRL校正，兩個頻帶的插入損耗值和反射損耗值在1.55 GHz為-1.417 dB及-16.23 dB，在2.4GHz則分別為-1.775 dB及-20.72 dB，全波模擬與量測結果有相當好的吻合度。 Dual-band filters designed for IEEE 802.11 and Bluetooth applications will be presented in this thesis. Generally, there are three main problems for filters with relatively large ratio of passband center frequencies: high insertion loss (more than 3dB), high return loss (less than -10dB) and bad selectivity. A new design of a compact dual-band bandpass filter using two different type resonators which are microstrip open-loop resonators and defected ground structure open-loop resonators is proposed and investigated in this paper. The proposed filter is composed of two bandpass filters using open-loop resonators located different metal layers and uses a way to external coupling which could have a pair of inherent zeros. By tuning zeros could control selectivity no need extra structure. A taper feed-in line could enhance external coupling to keep the response of the wider bandwidth. Since individual bandwidth and dual-band range of the proposed filter could adjust independently, the thesis will propose two dual-band bandpass filters designed for 2.4/5.2 GHz and 1.55/2.4 GHz. The measured insertion loss and return loss of 2.4/5.2 GHz application are -1.725 dB and -10.11 dB at 2.4 GHz and -1.364 dB and -24.24 dB at 5.5 GHz. The measured insertion loss and return loss of 1.55/2.4 GHz application are -1.417 dB and -16.23 dB at 1.55 GHz and -1.775 dB and -20.72 dB at 2.4 GHz, respectively. All circuits are fabricated on FR4 substrates and in good agreement with simulation.
