CN101916892A - Tunable Band-Stop Filter with Constant Absolute Bandwidth Based on Modular Structure - Google Patents
Tunable Band-Stop Filter with Constant Absolute Bandwidth Based on Modular Structure Download PDFInfo
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Abstract
本发明公开一种基于模块化结构的绝对带宽恒定的可调带阻滤波器,包括上层微带结构,中间层介质基板和下层接地金属板。滤波器可以由一个模块单元或者多个模块单元组成,每个模块单元中包括两个谐振器和主传输线;两个谐振器都是半波长谐振器,结构相同,关于微带结构的中心纵轴对称设置;主传输线包括耦合部分和非耦合部分;其耦合部分由第七微带线,第八微带线和第九微带线组成,依次连接构成n形结构,位于谐振器耦合部分n形结构的内侧;两个谐振器的变容二极管设置相同的偏置电压;本发明可用于各类可重构射频前端电路,具有频率调谐时绝对带宽恒定的特点。通过级联两个或多个模块单元,可得到频率选择性更高的绝对带宽恒定的可调带阻滤波器。
The invention discloses an adjustable band-stop filter with constant absolute bandwidth based on a modular structure, which comprises an upper-layer microstrip structure, a middle-layer dielectric substrate and a lower-layer grounded metal plate. The filter can be composed of one modular unit or multiple modular units, and each modular unit includes two resonators and the main transmission line; both resonators are half-wavelength resonators with the same structure, about the central longitudinal axis of the microstrip structure Symmetrically arranged; the main transmission line includes a coupling part and a non-coupling part; its coupling part is composed of the seventh microstrip line, the eighth microstrip line and the ninth microstrip line, which are connected in turn to form an n-shaped structure, located in the n-shaped resonator coupling part The inner side of the structure; the varactor diodes of the two resonators are set with the same bias voltage; the invention can be used in various reconfigurable radio frequency front-end circuits, and has the characteristic of constant absolute bandwidth during frequency tuning. By cascading two or more modular units, an adjustable band-stop filter with higher frequency selectivity and constant absolute bandwidth can be obtained.
Description
技术领域technical field
本发明涉及一种中心频率可调的带阻滤波器,特别是涉及一种基于模块化结构,中心频率调谐时绝对带宽恒定,可应用于射频前端电路中的可调带阻滤波器。The invention relates to a band-stop filter with adjustable center frequency, in particular to an adjustable band-stop filter based on a modular structure, whose absolute bandwidth is constant when the center frequency is tuned, and which can be applied to radio frequency front-end circuits.
背景技术Background technique
现代超宽带雷达和无线通信的发展需要高性能的可重构射频子系统,例如移动通信的发展要求小型化、多标准、多模式、多频带收发信机,为了适应该要求,射频前端需要根据工作模式来调节其工作频率和带宽。这类射频前端需要各种各样的射频可调滤波器来选择有用信号并抑制干扰信号,其中射频电调带阻滤波器是射频可调滤波器的一个重要类别。在多波段宽带收发信机和软件无线电的射频前端电路中,中心频率可调的带阻滤波器可用于抑制出现在强度较弱的有用信号频率附近的强干扰信号。The development of modern ultra-wideband radar and wireless communication requires high-performance reconfigurable RF subsystems. For example, the development of mobile communication requires miniaturized, multi-standard, multi-mode, and multi-band transceivers. In order to meet this requirement, the RF front-end needs to be based on Working mode to adjust its working frequency and bandwidth. This type of RF front-end requires a variety of RF tunable filters to select useful signals and suppress interference signals, among which RF electrically tunable band-stop filters are an important category of RF tunable filters. In the RF front-end circuits of multi-band broadband transceivers and software radios, band-stop filters with adjustable center frequencies can be used to suppress strong interference signals that appear near the frequency of weaker useful signals.
目前已经有多种可调带阻滤波器的设计方法,其中有几种典型的方法。第一种方法是通过调节与主传输线耦合的谐振器的谐振频率来调谐阻带的频率,如I.C.Hunter and J.D.Rhodes,“Electronically tunable microwave bandstop filters,”IEEE Trans.Microw.Theory Tech.,vol.MTT-30,no.9,pp.1361-1367,Sep.1982。第二种方法是采用集成了变容二极管的DGS(缺陷地)结构来设计可调带阻滤波器,如A.M.E.Safwat,F.Podevin,P.Ferrari and A.Vi lcot,“Tunable bandstop defected ground structure resonator using reconfigurable dumbbell-shaped coplanar waveguide,”IEEE Trans.Microw.Theory Tech.,vol.54,no.9,pp.3559-3564,Sep.2006。第三种方法是在阻带频率范围内调节谐振器的阻抗使之与源/负载阻抗相匹配,从而使信号能量在有耗振荡器中被吸收,如D.R.Jachowski,“Cascadable lossy passive biquad bandstop filter,”in IEEE MTT-S Int Microwave Symp.Dig.,pp.513-516,2005。At present, there are many design methods of tunable band-stop filters, among which there are several typical methods. The first method is to tune the frequency of the stopband by adjusting the resonant frequency of the resonator coupled to the main transmission line, as in I.C.Hunter and J.D.Rhodes, “Electronically tunable microwave bandstop filters,” IEEE Trans.Microw.Theory Tech., vol. MTT-30, no.9, pp.1361-1367, Sep.1982. The second method is to use the DGS (defective ground) structure integrated with varactor diodes to design tunable bandstop filters, such as A.M.E.Safwat, F.Podevin, P.Ferrari and A.Vi lcot, "Tunable bandstop defective ground structure resonator using reconfigurable dumbbell-shaped coplanar waveguide,” IEEE Trans. Microw. Theory Tech., vol.54, no.9, pp.3559-3564, Sep.2006. The third method is to adjust the impedance of the resonator to match the source/load impedance in the stopband frequency range, so that the signal energy is absorbed in the lossy oscillator, such as D.R. Jachowski, "Cascadable lossy passive biquad bandstop filter ,” in IEEE MTT-S Int Microwave Symp.Dig., pp.513-516, 2005.
不管采用何种滤波器设计方法,电调带阻滤波器设计都面临着两个问题:一是阻带中心频率调谐时阻带的绝对带宽会发生改变;二是高阶电调滤波器的设计问题,在设计高阶电调滤波器的时候必须调整每一级的设计参数而不能直接将两个低阶的带阻滤波器级联起来,导致设计复杂。No matter which filter design method is adopted, the design of the electronically tuned band-stop filter faces two problems: one is that the absolute bandwidth of the stop band will change when the center frequency of the stop band is tuned; the other is the design of high-order electronically tuned filters. The problem is that when designing a high-order electronically tuned filter, the design parameters of each stage must be adjusted instead of directly cascading two low-order band-stop filters, resulting in complex design.
发明内容Contents of the invention
本发明的目的在于针对现有技术存在的问题,提供一种基于模块化结构、中心频率调谐时绝对带宽恒定的可调带阻滤波器;基于模块化结构的绝对带宽恒定的可调带阻滤波器具有绝对带宽恒定的特性的;同时具有模块化设计特性,直接级联两个或两个以上可调带阻滤波器模块单元,可以得到频率选择性更高的带阻滤波器;基于模块化结构的绝对带宽恒定的可调带阻滤波器,可以解决中心频率调谐时阻带的绝对带宽发生改变的问题以及高阶滤波器设计不能直接级联的问题。The purpose of the present invention is to solve the problems existing in the prior art, to provide an adjustable band-stop filter based on a modular structure and having a constant absolute bandwidth when the center frequency is tuned; an adjustable band-stop filter based on a modular structure with a constant absolute bandwidth The filter has the characteristics of constant absolute bandwidth; at the same time, it has the characteristics of modular design, and directly cascades two or more adjustable band-stop filter module units to obtain a band-stop filter with higher frequency selectivity; based on modular The adjustable band-stop filter with a constant absolute bandwidth of the structure can solve the problem that the absolute bandwidth of the stop band changes when the center frequency is tuned and the problem that high-order filter designs cannot be directly cascaded.
为实现本发明目的,本发明所采用的技术方案如下:For realizing the object of the present invention, the technical scheme adopted in the present invention is as follows:
基于模块化结构的绝对带宽恒定的可调带阻滤波器,包括上层的微带结构,中间层的介质基板和下层的接地金属板;上层微带结构附着在中间层介质板上表面,中间层介质板下表面为接地金属;上层的微带结构包括两个谐振器和主传输线;两个谐振器都是半波长谐振器,结构相同,关于微带结构的中心纵轴对称设置;每个谐振器由微带线和变容二极管构成;两个谐振器的变容二极管设置相同的偏置电压;谐振器的微带线分为耦合部分与非耦合部分;谐振器的微带线耦合部分由第三微带线,第四微带线和第五微带线依次连接成n形结构;谐振器的微带线非耦合部分包括第一微带线,第二微带线和第六微带线;第一微带线的一端开路,另一端与第二微带线相连;第二微带线的另一端与第三微带线连接;第六微带线一端与第五微带线连接,另一端与变容二极管相连;变容二极管的另一端经穿过中间层介质基板的金属化过孔与下层接地金属相连;所述主传输线包括耦合部分和非耦合部分;其耦合部分由第七微带线,第八微带线和第九微带线依次连接构成n形结构,位于谐振器耦合部分n形结构的内侧;谐振器耦合部分和主传输线耦合部分之间设有宽度为0.1mm-0.8mm的电磁耦合间距;主传输线的非耦合部分包括端口微带线和连接微带线;连接微带线为蛇形线;连接微带线两侧对称设置端口微带线、第七微带线、第八微带线、第九微带线;端口微带线一端与第七微带线连接;连接微带线与第九微带线连接;所述连接微带线的长度其中c为光速,εr为介质基板的相对介电常数,fmin和fmax分别为谐振器的谐振频率f可调范围的最小值与最大值;谐振器的电长度L+ΔL为谐振频率f对应的波长λ的二分之一;其中,L为实际微带线长度,ΔL为变容二极管等效微带线长度;实际微带线长度L为第一微带线、第二微带线、第三微带线、第四微带线、第五微带线和第六微带线的长度之和;谐振器与主传输线之间的耦合方式是一种电耦合与磁耦合混合的耦合方式,耦合区间的长度等于第三微带线,第四微带线和第五微带线的长度总和;在最高谐振频率fmax和最低谐振频率fmin上谐振器总的等效微带线的中点落在耦合区间内;该耦合区间内电磁耦合中磁耦合占主导地位,耦合强度随着频率的增加而减小。An adjustable band-stop filter with constant absolute bandwidth based on a modular structure, including the upper microstrip structure, the dielectric substrate of the middle layer and the grounded metal plate of the lower layer; the upper microstrip structure is attached to the upper surface of the middle dielectric board, and The lower surface of the dielectric plate is grounded metal; the upper microstrip structure includes two resonators and the main transmission line; the two resonators are half-wavelength resonators with the same structure, and are symmetrically arranged about the central longitudinal axis of the microstrip structure; each resonator The resonator is composed of a microstrip line and a varactor diode; the varactor diodes of the two resonators set the same bias voltage; the microstrip line of the resonator is divided into a coupling part and an uncoupling part; the microstrip line coupling part of the resonator is composed of The third microstrip line, the fourth microstrip line and the fifth microstrip line are sequentially connected to form an n-shaped structure; the uncoupled part of the microstrip line of the resonator includes the first microstrip line, the second microstrip line and the sixth microstrip line line; one end of the first microstrip line is open, and the other end is connected to the second microstrip line; the other end of the second microstrip line is connected to the third microstrip line; one end of the sixth microstrip line is connected to the fifth microstrip line , the other end is connected to the varactor diode; the other end of the varactor diode is connected to the ground metal of the lower layer through the metallized via hole passing through the intermediate layer dielectric substrate; the main transmission line includes a coupling part and a non-coupling part; The seven microstrip lines, the eighth microstrip line and the ninth microstrip line are sequentially connected to form an n-shaped structure, which is located inside the n-shaped structure of the resonator coupling part; a width of 0.1 is provided between the resonator coupling part and the main transmission line coupling part. The electromagnetic coupling spacing of mm-0.8mm; the uncoupled part of the main transmission line includes the port microstrip line and the connecting microstrip line; the connecting microstrip line is a serpentine line; the port microstrip line is symmetrically arranged on both sides of the connecting microstrip line, the seventh Microstrip line, the eighth microstrip line, and the ninth microstrip line; one end of the port microstrip line is connected to the seventh microstrip line; the connecting microstrip line is connected to the ninth microstrip line; the length of the connecting microstrip line Where c is the speed of light, ε r is the relative permittivity of the dielectric substrate, f min and f max are the minimum and maximum values of the adjustable range of the resonant frequency f of the resonator respectively; the electrical length L+ΔL of the resonator is one-half of the wavelength λ corresponding to the resonant frequency f; among them, L is the actual The length of the microstrip line, ΔL is the equivalent microstrip line length of the varactor diode; the actual microstrip line length L is the first microstrip line, the second microstrip line, the third microstrip line, the fourth microstrip line, the fifth The sum of the lengths of the microstrip line and the sixth microstrip line; the coupling mode between the resonator and the main transmission line is a coupling mode in which electrical coupling and magnetic coupling are mixed, and the length of the coupling interval is equal to the third microstrip line, the fourth The sum of the lengths of the microstrip line and the fifth microstrip line; the midpoint of the total equivalent microstrip line of the resonator on the highest resonant frequency f max and the lowest resonant frequency f min falls within the coupling interval; the electromagnetic coupling in this coupling interval The magnetic coupling is dominant in the middle, and the coupling strength decreases with the increase of frequency.
为进一步实现本发明目的,所述可调带阻滤波器的可调谐振频率范围为1.73-2.2GHz,其中,第一微带线和第三微带线的长度为5.6mm,第二微带线的长度为1.88mm,第四微带线的长度为3.75mm,第五微带线的长度为9.8mm,第七微带线与第九微带线之间的间距为2mm,第六微带线的长度为1.7mm,谐振器与主传输线之间的耦合间距为0.12mm,第六微带线的宽度为0.7mm,连接微带线的宽度为0.3mm,第一微带线和第二微带线的宽度为0.7mm,第三微带线、第四微带线和第五微带线的宽度为0.4mm,第七微带线、第八微带线和第九微带线的宽度为0.8mm,端口微带线的宽度为1.9mm,端口微带线的特性阻抗为50Ω。连接微带线的长度L12为25.4mm。In order to further realize the object of the present invention, the adjustable resonant frequency range of the adjustable band-stop filter is 1.73-2.2GHz, wherein the length of the first microstrip line and the third microstrip line is 5.6mm, and the length of the second microstrip line The length of the line is 1.88mm, the length of the fourth microstrip line is 3.75mm, the length of the fifth microstrip line is 9.8mm, the distance between the seventh microstrip line and the ninth microstrip line is 2mm, the sixth microstrip line The length of the stripline is 1.7mm, the coupling spacing between the resonator and the main transmission line is 0.12mm, the width of the sixth microstrip line is 0.7mm, the width of the connecting microstrip line is 0.3mm, the first microstrip line and the second The width of the second microstrip line is 0.7mm, the width of the third microstrip line, the fourth microstrip line and the fifth microstrip line is 0.4mm, the seventh microstrip line, the eighth microstrip line and the ninth microstrip line The width of the port microstrip line is 0.8mm, the width of the port microstrip line is 1.9mm, and the characteristic impedance of the port microstrip line is 50Ω. The length L 12 of the connecting microstrip line is 25.4 mm.
两个相同的可调带阻滤波器模块单元通过50Ω传输线连接得到两级的可调带阻滤波器,传输线的长度大于介质基板厚度的1.5倍。Two identical adjustable band-stop filter module units are connected through a 50Ω transmission line to obtain a two-stage adjustable band-stop filter, and the length of the transmission line is greater than 1.5 times the thickness of the dielectric substrate.
相对于现有技术,本发明具有如下优点:Compared with the prior art, the present invention has the following advantages:
(1)绝对带宽恒定。对于普通的可调带阻滤波器,当阻带的中心频率调谐时其绝对带宽会发生改变,本发明的实施实例中的带阻滤波器的中心频率在调谐时绝对带宽保持恒定,优于普通的可调带阻滤波器。(1) The absolute bandwidth is constant. For common adjustable band-stop filters, when the center frequency of the stop band is tuned, its absolute bandwidth will change. The center frequency of the band-stop filter in the embodiment of the present invention keeps constant when tuning, which is better than ordinary band-stop filters. adjustable band-stop filter.
(2)模块化结构。可以方便地级联多个模块单元形成高阶滤波器来提高频率选择性。用普通的带阻滤波器结构来设计高阶电调滤波器时必须调整每一级的设计参数而不能直接将两个普通的低阶带阻滤波器级联起来,导致设计复杂。本发明中的模块单元是模块化对称结构,从两端口看进去的阻抗是相同的,当两端口的阻抗都调整到50Ω时,就可以直接把两个模块单元级联起来实现高阶滤波器,从而提高其频率选择性。(2) Modular structure. Multiple modular units can be easily cascaded to form high-order filters to improve frequency selectivity. When designing a high-order electronically tunable filter with a common band-stop filter structure, it is necessary to adjust the design parameters of each stage instead of directly cascading two common low-order band-stop filters, resulting in a complex design. The module unit in the present invention is a modular symmetrical structure, and the impedance seen from the two ports is the same. When the impedance of the two ports is adjusted to 50Ω, the two module units can be directly cascaded to realize a high-order filter , thereby improving its frequency selectivity.
附图说明Description of drawings
图1是基于模块化结构的绝对带宽恒定的可调带阻滤波器的一个模块单元的结构图;Fig. 1 is the structural diagram of a module unit of the constant adjustable band stop filter based on the absolute bandwidth of modular structure;
图2(a)是可调带阻滤波器的电磁耦合结构的等效原理图;Fig. 2 (a) is the equivalent schematic diagram of the electromagnetic coupling structure of the adjustable band-stop filter;
图2(b)是可调带阻滤波器的谐振器在不同偏置电压下的等效电路图;Fig. 2 (b) is the equivalent circuit diagram of the resonator of the adjustable band-stop filter under different bias voltages;
图3是采用一个模块单元的可调带阻滤波器的结构示意图;Fig. 3 is a schematic structural diagram of an adjustable band-stop filter using a modular unit;
图4是采用一个模块单元的可调带阻滤波器的传输特性曲线图;Fig. 4 is a transmission characteristic curve diagram of an adjustable band-stop filter adopting a modular unit;
图5是采用两个模块单元的可调带阻滤波器的结构示意图;Fig. 5 is a structural schematic diagram of an adjustable band-stop filter using two modular units;
图6是采用两个模块单元的可调带阻滤波器的传输特性曲线图。Fig. 6 is a curve diagram of transmission characteristics of an adjustable band-stop filter using two modular units.
具体实施方案specific implementation plan
下面结合附图对本发明作进一步详细的说明,但本发明要求保护的范围并不局限于下例表述的范围。The present invention will be described in further detail below in conjunction with the accompanying drawings, but the scope of protection claimed by the present invention is not limited to the scope of the following examples.
如图1所示,基于模块化结构的绝对带宽恒定的可调带阻滤波器包括上层的微带结构,中间层的介质基板和下层的接地金属板;上层微带结构附着在中间层介质板上表面,中间层介质板下表面为接地金属;上层的微带结构包括两个谐振器和主传输线;两个谐振器都是半波长谐振器,结构相同,关于微带结构的中心纵轴对称设置;每个谐振器由微带线和变容二极管7构成;谐振器的微带线分为耦合部分与非耦合部分;谐振器的微带线耦合部分由第三微带线3,第四微带线4和第五微带线5依次连接成n形结构;谐振器的微带线非耦合部分包括第一微带线1,第二微带线2和第六微带线6;第一微带线1的一端开路,另一端与第二微带线2相连;第二微带线2的另一端与第三微带线3连接;第六微带线6一端与第五微带线5连接,另一端与变容二极管管7相连;变容二极管7的另一端通过介质基板的金属化过孔与下层的接地金属板相连。主传输线关于微带结构的中心纵轴对称设置,包括耦合部分和非耦合部分;耦合部分由第七微带线9,第八微带线10和第九微带线11依次连接构成n形结构,位于谐振器耦合部分n形结构的内侧。主传输线的非耦合部分包括端口微带线8和连接微带线12;连接微带线12为蛇形线;连接微带线12两侧对称设置端口微带线8、第七微带线9、第八微带线10、第九微带线11;端口微带线8一端与第七微带线9连接;连接微带线12与第九微带线11连接;端口微带线8与第二微带线2平行,彼此间距大于介质基板厚度的1.5倍,防止发生电磁耦合;端口微带线8的特性阻抗为50Ω;谐振器耦合部分和主传输线耦合部分之间设有宽度为0.1mm-0.8mm的电磁耦合间距,实现电磁耦合;电磁耦合间距由耦合强弱来决定。主传输线的连接微带线12起到阻抗变换的作用,连接微带线12的长度其中c为光速,εr为介质基板的相对介电常数,fmin和fmax分别为谐振器的谐振频率f可调范围的最小值与最大值。As shown in Figure 1, the tunable band-stop filter with constant absolute bandwidth based on the modular structure includes the upper microstrip structure, the middle dielectric substrate and the lower ground metal plate; the upper microstrip structure is attached to the middle dielectric plate The upper surface and the lower surface of the intermediate dielectric plate are grounded metal; the upper microstrip structure includes two resonators and the main transmission line; both resonators are half-wavelength resonators with the same structure, symmetrical about the central longitudinal axis of the microstrip structure setting; each resonator is made of a microstrip line and a
谐振器由微带线和变容二极管组成,微带线一端连接一个变容二极管,另一端开路;谐振器的第一微带线1,第二微带线2,第三微带线3,第四微带线4,第五微带线5和第六微带线6长度和加上变容二极管7等效的微带线的总长度为滤波器谐振频率上的半波长。谐振器的谐振频率主要通过变容二极管的偏置电压来调节。在忽略寄生效应时,变容二极管可以等效成一段终端开路的微带线。如图2(a)所示,斜线区域表示真实的微带线,长度为L;网格区域表示变容二极管等效成的微带线,长度为ΔL;谐振器的电长度L+ΔL为谐振频率f对应的波长λ的二分之一;谐振频率f与电长度成反比,即调整谐振器的变容二极管7的偏置电压,则变容二极管7的等效电容会发生改变,其等效微带线长度也会随之改变,从而谐振频率发生变化;如图2(b)所示,当变容二极管的等效电容Cv1>Cv2时,对应的等效微带线长度ΔL1>ΔL2,对应的谐振频率f1<f2。因此通过调整变容二极管的偏压,可以调整阻带滤波器的中心频率。选定变容二极管7和确定滤波器工作的谐振频率调谐范围fmin、fmax之后,可以确定变容二极管的等效微带线长度的变化范围,然后根据等效微带线的总长度为半波长的特性就可以确定实际微带线的长度L。实际微带线长度L为图1中第一微带线1、第二微带线2、第三微带线3、第四微带线4、第五微带线5和第六微带线6的长度之和。The resonator is composed of a microstrip line and a varactor diode. One end of the microstrip line is connected to a varactor diode, and the other end is open circuit; the
基于模块化结构的绝对带宽恒定的可调带阻滤波器的谐振器与主传输线采用的耦合方式是一种混合电磁耦合方式。如图1所示,耦合结构由第三微带线3、第四微带线4,第五微带线5,第七微带线9,第八微带线10,第九微带线11组成。谐振器与主传输线的耦合结构可用导纳变换器J01表示,谐振器可以等效为电感和电容的并联,变容二极管电容通过偏置电压控制。根据J.S.Hong and M.J.Lancaster,Microwave Filter for RF/Microwave Application,New York:John wiley,2001.书中介绍的经典滤波器设计理论以及滤波器模块单元的电路结构,可得所要求的其中Cv为变容二极管电容,Δw为滤波器阻带的绝对带宽,Z0为应用滤波器的射频电路的特征阻抗。由于J01与谐振器和主传输线之间的耦合系数|K|成正比,可得当变容二极管的电容Cv减小时,谐振频率f增大。由上述关系可得,阻带中心频率调谐时阻带的绝对带宽Δw恒定不变的理论要求为:耦合系数|K|要随着阻带中心频率的增大而减小。该理论要求可以通过下列方式实现:耦合区间如图2(a)中的虚线部分所示,谐振器耦合部分微带线的长度须使变容二极管7在最低偏置电压下和最高偏置电压下的谐振器总等效微带线的中点都在谐振器耦合部分微带线上,即在最高谐振频率fmax和最低谐振频率fmin上谐振器总的等效微带线的中点落在耦合区间内,使得电磁耦合中磁耦合占主导地位。在此基础上,调整耦合区间的大小即调整图2(a)中d1和d2的位置。在此耦合区间,磁耦合强度随频率的增大而减小,电耦合强度随阻带中心频率的增大而增大,而总的耦合强度为磁耦合强度减去电耦合强度,因此总的耦合系数就会随着频率的增大而减小,从而可以满足阻带中心频率调谐时绝对带宽保持恒定的理论要求。耦合区间的长度d2-d1等于第三微带线3,第四微带线4和第五微带线5的长度总和;第一微带线1与第二微带线2长度之和为d1;第六微带线长度为L-d2。耦合区间中的微带线之间的耦合间距决定了总的耦合强度,耦合间距越小,则总的耦合强度越强。The coupling method between the resonator and the main transmission line of the adjustable band-stop filter with constant absolute bandwidth based on the modular structure is a hybrid electromagnetic coupling method. As shown in Figure 1, the coupling structure consists of the third microstrip line 3, the
两个谐振器和主传输线关于微带结构的中心纵轴对称设置,从左右两端看进去,有相同的阻抗特性,构成一个模块单元;通过级联两个或多个模块单元,可得到频率选择性更高的绝对带宽恒定的可调带阻滤波器。The two resonators and the main transmission line are arranged symmetrically about the central longitudinal axis of the microstrip structure. When viewed from the left and right ends, they have the same impedance characteristics and form a modular unit; by cascading two or more modular units, the frequency can be obtained Higher selectivity tunable band-stop filter with constant absolute bandwidth.
实施例Example
基于模块化结构的绝对带宽恒定的可调带阻滤波器的一个模块单元的结构如图1所示,有关尺寸规格如下图3所示。介质基板的厚度为0.76mm,相对介电常数为2.94,损耗角正切为0.0012。连接微带线12采取蛇形折线结构,可以减小电路尺寸。变容二级管7采用Toshiba的1sv277,变容二级管的一端通过金属化过孔接地。连接微带线12的总长度L12是25.4mm,是可调谐振频率范围的中心频率的四分之一波长。如图3所示,滤波器的各微带线尺寸参数如下:第一微带线1和第三微带线3长度L1=5.6mm;第二微带线2长度L2=1.88mm,第四微带线4长度L3=3.75mm,第五微带线5长度L4=9.8mm,第七微带线9与第九微带线11之间的间距L5=2mm,第六微带线6长度L6=1.7mm,谐振器与主传输线之间的耦合间距g1=0.12mm,第六微带线6宽度W1=0.7mm,连接微带线12宽度W2=0.3mm,第一微带线1和第二微带线2宽度W4=0.7mm,第三微带线3、第四微带线4和第五微带线5的宽度W3=0.4mm,第七微带线9、第八微带线10和第九微带线11的宽度W5=0.8mm,端口微带线8宽度W6=1.9mm。选择这些微带线各自的长度和宽度,以获得所需的输入/输出阻抗特性、频带内传输特性和频带外衰减特性。图4是按照上述参数设计出来的采用一个模块单元的可调带阻滤波器的仿真和实际测试的结果;传输特性曲线图中的横轴表示频率,纵轴表示传输特性|S21|;虚线为仿真结果,实线为测试结果。测试结果与仿真结果一致,仿真和测试分别是使用安捷伦公司的商业电磁仿真软件ADS和E5071C网络分析仪来完成的。由测试结果可见,阻带的中心频率可以在1.73-2.2GHz范围内进行调节;图4中的传输特性曲线是在阻带中心频率分别为1.73GHz、1.8GHz、1.9GHz、2.0GHz、2.1GHz、2.2GHz时测得,以带阻滤波器常用的-20dB抑制水平作为标准,-20dB处的带宽分别为48MHz、48MHz、49MHz、52MHz、53MHz、53MHz;由此可见,-20dB处的带宽为50±3MHz,意味着频率调谐时绝对带宽几乎保持不变。测试结果说明,该实施例实现了本发明所要达到的绝对带宽恒定的目标。The structure of a modular unit of an adjustable band-stop filter with constant absolute bandwidth based on a modular structure is shown in Figure 1, and the relevant dimensions are shown in Figure 3 below. The thickness of the dielectric substrate is 0.76mm, the relative permittivity is 2.94, and the loss tangent is 0.0012. The connecting
图5是采用两个模块单元的可调带阻滤波器的结构示意图,采用两个模块单元的目的是为了提高阻带的抑制水平。滤波器模块单元的左右两端口具有相同的阻抗特性,当这两个端口的阻抗都调整到50Ω时就可以直接把两个模块单元级联起来提高频率选择性,实现高阶滤波器。通过50Ω传输线13将图1中的两个相同滤波器模块单元级联起来得到频率选择性更高的可调带阻滤波器;为了避免两个滤波器模块单元发生互耦,传输线13的长度应大于介质基板厚度的1.5倍。图6是采用两个模块单元的可调带阻滤波器的仿真和实际测试的结果,传输特性图中的横轴表示频率,纵轴表示传输特性|S21|;虚线为仿真结果,实线为测试结果;仿真和测试分别是使用安捷伦公司的商业电磁仿真软件ADS和E5071C网络分析仪来完成的。测试结果表明,阻带中心频率可以在1.73-2.2GHz范围内进行调谐;图6中的传输特性曲线是在阻带中心频率分别为1.73GHz、1.8GHz、1.9GHz、2.0GHz、2.1GHz、2.2GHz时测得,-40dB处的带宽分别为58MHz、62MHz、61MHz、62MHz、58MHz、57MHz;由此可见,-40dB处的带宽为60±3MHz,意味着随着阻带中心频率的调谐,阻带的绝对带宽保持恒定不变,实现了带宽恒定的目标。FIG. 5 is a schematic structural diagram of an adjustable band-stop filter using two modular units. The purpose of using two modular units is to improve the suppression level of the stop band. The left and right ports of the filter module unit have the same impedance characteristics. When the impedance of the two ports is adjusted to 50Ω, the two module units can be directly cascaded to improve frequency selectivity and realize a high-order filter. Two identical filter module units in Fig. 1 are cascaded through a 50Ω transmission line 13 to obtain an adjustable band-stop filter with higher frequency selectivity; in order to avoid mutual coupling between the two filter module units, the length of the transmission line 13 should be Greater than 1.5 times the thickness of the dielectric substrate. Figure 6 is the simulation and actual test results of the adjustable band-stop filter using two modular units. The horizontal axis in the transmission characteristic graph represents the frequency, and the vertical axis represents the transmission characteristic |S 21 |; the dotted line is the simulation result, and the solid line For the test results; the simulation and test were completed using Agilent's commercial electromagnetic simulation software ADS and E5071C network analyzer respectively. The test results show that the center frequency of the stop band can be tuned in the range of 1.73-2.2GHz; Measured at GHz, the bandwidths at -40dB are 58MHz, 62MHz, 61MHz, 62MHz, 58MHz, and 57MHz respectively; it can be seen that the bandwidth at -40dB is 60±3MHz, which means that with the tuning of the center frequency of the stopband, the stopband The absolute bandwidth of the band remains constant, achieving the goal of constant bandwidth.
实施例的仿真和测试结果表明,当阻带的中心频率调谐时,实施例中的绝对带宽基本保持不变,实现了绝对带宽恒定的目标。本发明具有模块化特性,通过简单的级联就可以实现频率选择性更高的可调带阻滤波器。The simulation and test results of the embodiment show that when the center frequency of the stop band is tuned, the absolute bandwidth in the embodiment remains basically unchanged, and the goal of constant absolute bandwidth is achieved. The invention has a modular feature, and can realize an adjustable band rejection filter with higher frequency selectivity through simple cascading.
以上所述仅为本发明的较佳实例而已,并不用以限制本发明,凡在本发明的精神和原则之内,所作的任何修改、等同替换、改进等,均应包含在本发明的保护范围之内。The above descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.
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