新式雙金屬平面帶通濾波器之設計

Design of Novel Dual-Metal-Plane Bandpass Filters

林士程(Shih-Cheng Lin)

指導教授 ： 陳俊雄

國立臺灣大學/電機資訊學院/電信工程學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.00621

摘要

本論文的中心思想在於追求微波帶通濾波器之寬贅餘頻帶的抑制、所佔電路面積之精縮、頻率選擇度的銳利程度以及較寬的可實現頻寬。基於這些動機，本論文主要專注於三種不同之創新濾波器架構，進而使得這些嚴格的濾波器規格可實現。此研究主要在於研究使用單一基板之雙金屬平面組態，此種組態提供了另一種遠優於傳統單平面電路的實現方法並提供多種優點。適當地使用雙金屬平面組態，可以大幅的便利多種新型濾波器之設計及實作，諸如擁有寬贅餘頻帶壓制之「電容加載共軸共平面波導濾波器」、運用於擁有傳輸零點之精縮型濾波器之「貼片─連通柱─螺旋共振器」，以及擁有較寬可實現頻寬之「複合式左手�右手傳輸線濾波器」。
起初，為了達成贅餘頻帶之壓制，基本上由四分之一波長步階阻抗共振器所組成的，使用強化型的空橋電容加載於共軸共平面波導濾波器，結合特殊設計的微帶線到共平面波導轉接的耦合架構來同時達到贅餘頻帶之壓抑以及尺寸之縮減。首先，適當地設計印製在共平面波導上方之強化型空橋以達成所需加載電容值，並選擇適當之共振器參數，以符合所提出之特殊條件，藉以抑制低階數之贅餘頻帶。接著，採用經過調整之寬邊耦合微帶線到共平面波導之轉接來同時提供所需之餽入電容並同時達成對於較高頻段之高衰減程度。這三種贅餘頻帶壓抑的機制皆被詳細的探討並由模擬與實驗佐證。此創新濾波器在四階的實現實例中可將止帶延伸至19.04倍之中心頻率。
接著，為了同時達成濾波器的尺寸精縮並提供陡峭的頻率選擇度，基於雙平面組態之「貼片─連通柱─螺旋共振器」被提出並驗證。共振器組成是用位於上平面之微帶貼片作為電容，然後經由一貫穿基板之連通柱連接到位於下平面之準集總螺旋形電感。因為此種共振器架構位於單一基板之相反側，因而能夠在印刷電路板製程中實現出非常精縮之尺寸。在實現帶通濾波器時，適當地結合所提出之共振器，可組成四種有用的耦合共振器對，這些耦合共振器對便可同時提供延著相反金屬面之電性及磁性的耦合來達成所需求之濾波器響應。適當地將共振器對間的耦合設計成同相或者是反相，一個不需要傳統交叉耦合路徑或者是輸入輸出間耦合之二階帶通濾波器可被實現成擁有柴比雪夫或者類準橢圓形函數之濾波器響應。而為了設計考量，此二階濾波器的相關等效電路亦被周詳的推導及驗證。最後，設計概念被延伸至設計四階貼片─連通柱─螺旋帶通濾波器，此高階濾波器提供絕佳的通帶選擇度，同時只佔有0.188波長乘0.043波長的精縮尺寸。
最後，為了實現擁有較寬可實現頻寬之帶通濾波器，複合式右手�左手傳輸線濾波器也一樣在所提出之雙金屬平面組態上被實現出來，並同時採用共平面波導以及微帶線以利設計。藉由適當調整一個由可任意控制電容�電感集總元件所組成之複合式右手�左手單元，所需濾波器中心頻率以及比例頻寬可以很輕易地被實現出來，將數個單元串接，即可實現出帶通濾波響應。更明確地來說，相較於傳統那類基於假設狹窄頻寬之濾波器，這裡所提出的濾波器可提供相當寬頻的響應。為了展示起見，兩個雙平面濾波器被設計在不同的中心頻率並擁有不同的比例頻寬；此兩個濾波器在通道附近顯現相當良好的選擇度。此外，全波模擬與實驗量測的結果，兩者間有十分吻合的一致性。另外，研究中發現前面提出藉由串接數個複合式左手�右手單元來達成較寬可實現頻寬之途徑，當應用於實現較窄頻寬之濾波器時，容易出現不切實際而無法實現之集總元件值，於是利用零階共振器的特性，配合電感性耦合組抗倒反器的概念，較窄頻的濾波器亦可利用所提出之雙面複合式右手�左手單元加以實現。

關鍵字

Dual-metal-plane ； bandpass filter ； coplanar waveguide ； stepped-impedance resonator ； spurious suppression ； miniaturized ； patch-via-spiral resonator ； broadband ； composite right/left-handed transmission line

並列摘要

Pursuit of wider rejection bandwidth, compactness of occupied circuit size, sharpness of frequency selectivity, and broader realizable passband is the controlling idea among the overall dissertation. For this reason, this dissertation principally focuses on three different filter topologies so as to make the stringent requirements possible. The central concept is making good use of dual-metal-plane configuration which provides numerous advantages superior than those of conventional uniplanar approach. In this work, the dual-metal-plane configuration ultimately facilitates the designs of inline coplanar waveguide (CPW) filters with wideband spurious suppression, patch-via-spiral resonators for the development of miniaturized filters, and composite right/left-handed filters with wide fractional-bandwidth.
In the beginning, for the sake of spurious suppression, inline CPW bandpass filters composed of quarter-wavelength stepped-impedance resonators are proposed, using loaded air-bridge enhanced capacitors and broadside-coupled microstrip-to-CPW transition structures for both wide-band spurious suppression and size miniaturization. Three effective spurious suppression mechanisms including spurious destruction, spurious cancellation, and higher order spurious attenuation are incorporated in the proposed CPW filters and thus make the filter stopband extended up to 19.04f0.
Next, to achieve the filter miniaturization and simultaneously provide sharper passband, a novel patch-via-spiral resonator based on the dual-metal-plane configuration is proposed and examined. With the microstrip patch on the top plane serving as a capacitor and linking to the quasi-lumped spiral inductor on the bottom plane through a connecting via, the proposed dual-plane resonator structure located on the opposite sides of single substrate may form a miniaturized one in the printed-circuit board fabrication. By appropriately arranging the proposed patch-via-spiral resonators, useful coupled-resonator pairs may be constructed to provide electric and magnetic couplings along top- and bottom-planes, respectively. Therefore, the two couplings existing between coupled-resonator pair can be made with the same or opposite sign and are first carefully examined in 2nd-order filters with either Chebyshev or quasi-elliptic-like response. Then, the design concept is generally extended to 4th-order filters which possess good frequency selectivity and compact sizes of 0.188λg0 × 0.043λg0, where λg0 stands for the guided wavelength at center frequency.
Finally, in order to realize the filters with wide fractional-bandwidth, composite right/left-handed bandpass filters with wide fractional bandwidth are also implemented based on the proposed dual-metal-plane configuration. With proper design of the symmetric composite right/left-handed unit cell composed of arbitrarily adjustable lumped-elements, the passband, as well as the fractional bandwidth, can be constructed. Specifically, the implemented filters possess relatively achievable wide bandwidth in comparison with the conventional filters based on the assumption of narrow fractional-bandwidth. Besides, the approach for realizing the filters requiring broad bandwidth by cascading multiple CRLH-TL unit cells is found not suitable for filters demanding narrow bandwidth, since the corresponding lumped-element values are not practical in implementation. For this reason, by means of ZORs and inductively-coupled impedance inverters, one may easily design a filter with narrow bandwidth around 10%.

並列關鍵字

雙金屬平面 ； 帶通濾波器 ； 共平面波導 ； 步階性阻抗共振器 ； 贅餘頻帶抑制 ； 縮小化 ； 貼片-連通柱-螺旋共振器 ； 寬頻 ； 複合式右手/左手傳輸線

參考文獻

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