Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/203—Strip line filters
  • H01P1/20327—Electromagnetic interstage coupling
  • H01P1/20354—Non-comb or non-interdigital filters
  • H01P1/20381—Special shape resonators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/202—Coaxial filters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/203—Strip line filters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/203—Strip line filters
  • H01P1/20327—Electromagnetic interstage coupling
  • H01P1/20354—Non-comb or non-interdigital filters
  • H01P1/20363—Linear resonators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/207—Hollow waveguide filters
  • H01P1/209—Hollow waveguide filters comprising one or more branching arms or cavities wholly outside the main waveguide

Definitions

• the invention relates to a high-frequency bandpass filter arrangement, consisting of a main resonator and at least one blocking resonator coupled to the main resonator, the main resonator being defined by a line piece delimited on both sides by discontinuities in the form of an interruption or metal wall, and one at a center frequency Has electromagnetic natural vibration.
• the invention relates to the construction of bandpass filters from coupled resonators for the highly selective filtering of high-frequency electromagnetic signals in one
• Operating frequency range which is above approx. 0.5 GHz and below approx. 100 GHz.
• High-frequency bandpass filters form an important component in systems of communication technology, such as B. in terrestrial and satellite-based broadcasting, radio and cellular as well as in radar and navigation systems.
• B. in radio receivers individual filters the function of preselection, that is the negative pressure of unwanted interference signals and filter banks the function of frequency sewerage.
• individual bandpass filters are used, among other things, to suppress out-of-band spectral components in the output signal of the amplifiers, and filter banks are used in the form of output multiplexers Merging different carrier signals on a common antenna.
• passive electromagnetic filters With high-frequency bandpass filters, a distinction can first be made between active and passive designs. If high demands are placed on linearity and low noise, only the passive filters considered further here can be considered.
• the function of passive electromagnetic filters is based on the storage of electrical and magnetic field energy. In the case of filters made of discrete components, the storage of electrical and magnetic field energy takes place separately from one another, in a finite number of spatially separated discrete elements, namely in capacitors and inductors. Since the geometrical dimensions of these discrete components have to be much smaller than the operating wavelength, typically less than one tenth of the guided wavelength, and on the other hand the idle quality of these components decreases sharply with a reduction in dimensions, structures are preferred for steep-sided filters above approx. 1 GHz Coupled resonators used instead of interconnections of discrete capacitors and inductors.
• Coaxial resonators or cavity resonators are formed from coaxial TEM line pieces and waveguide pieces, in which the electromagnetic field is completely enclosed by conductive surfaces. These resonators can partially or to reduce the volume and change the spatial field profile completely filled with low loss dielectric material. In dielectric resonators, the field is mainly enclosed by the interface between the dielectric material and the surrounding air, and the field that decays outwardly from this interface is shielded by a metal housing, if necessary.
• Planar resonators which include microstrip, stripline and coplanar resonators, consist of planar interconnects on a dielectric substrate.
• the selection of the design of the resonators is u. a. influenced by the idling quality of the resonators required by the filter specification (see below).
• a high idling quality means a relatively large geometric dimension of the resonators.
• the volume available for all the resonators of a filter is limited in the lower GHz range. The volume requirement is reduced by approx. 50% by using resonators in two ways using orthogonal modes
• the electrical behavior of a bandpass filter is characterized by the frequency bandwidth (passband width) and the position of the passband, by the maximum insertion loss and minimum reflection attenuation in the passband, by the width of the transition areas between the passband and the stopband, and by the minimum blocking attenuation in the stopband.
• the number N of attenuation zeros (reflection zeros) in the pass band and the number M of attenuation poles (transmission zeros) at finite frequencies in the stop band are used. This characterization by reflection zeros and transmission zeros is based on the behavior in the (fictitious) lossless case and zeros are paid several times according to their order.
• the number N of the necessary zero damping points and thus the minimum number of necessary resonators follows.
• the necessary number N of damping zeros in the pass band decreases monotonically with increasing M / N.
• the way in which filters from coupled resonators are predominantly used today to produce transmission zeros consists in the introduction of couplings between non-directly adjacent resonators (“overcouplings”), in addition to the direct couplings of neighboring resonators.
• This bandstop is used to eliminate interference frequencies that are outside the pass band.
• M 0.
• a bandstop is connected in series to the filter second gate.
• a band-stop filter with two separated blocking ranges can also be used instead of a bandpass filter.
• the used pass band lies between the two band band stop band.
• Capacitive-coupled stub lines can also be used instead of the galvanically coupled stub lines.
• a continuous transmission line with stub lines (branch lines) coupled to it is also known from DE 24 42 618 C2.
• a disadvantage of the use of such filter structures from a main line with N passing from the filter input to the filter output R coupled stub lines as blocking resonators is the fact that the high blocking attenuation remains limited to frequency ranges of finite width and thus lets the filter through again beyond these ranges.
• the second disadvantage is that the number N of the dampers in the utilized passband between the two blocking ranges gs zeros is less than the number of resonators and thus the maximum steepness of the filter flanks between the pass band and the stop band that can be achieved for a given resonator number N R cannot be achieved.
• the object is achieved according to the invention by the subjects presented in the claims.
• bandpass filter structures are proposed in which blocking resonators are integrated into the structure in such a way that each blocking resonator realizes both one of the desired transmission zero points in the blocking area and, together with the rest of the filter structure, a damping zero point in the pass band.
• the length of the main resonator will be like this chosen so that it corresponds approximately to half the line wavelength at the center frequency of the bandpass filter.
• the blocking frequency of the one blocking resonator is chosen to be lower and that of the other blocking resonator is chosen to be larger than the center frequency and as a result each of the two blocking resonators generates a transmission zero and an additional pole by interaction with the main resonator.
• a single impedance-symmetrical filter element serves as a bandpass filter, one end of the main resonator is coupled electrically, galvanically or magnetically to the filter input and the other end to the filter output.
• the bandpass filter is constructed from a cascade of several impedance-symmetrical filter elements, the adjacent main resonator ends that are not coupled to the input or output port are electrically, galvanically or magnetically coupled.
• the length of the main resonator is chosen so that it is approximately the same corresponds to m times half the line wavelength at the center frequency and the distance between the outer blocking resonator pairs and the ends of the main resonator is approximately a quarter line wavelength.
• the blocking frequencies of the two blocking resonators of each of the m blocking resonator pairs are chosen such that one is smaller and the other larger than the center frequency, and thereby each of the two blocking resonators generates a transmission zero and by interacting with it Main resonator an additional pole.
• a single impedance-symmetrical filter element serves as a bandpass filter, one end of the main resonator is coupled to the filter output and the other end is electrically, galvanically or magnetically coupled to the filter output.
• the bandpass filter is constructed from a cascade of several impedance-symmetrical filter elements, the adjacent main resonator ends that are not coupled to the input or output port are electrically, galvanically or magnetically coupled.
• the impedance-unbalanced filter elements consist of a main resonator whose length corresponds to approximately a quarter of the line wavelength at the center frequency of the bandpass filter, in which one end is coupled to the adjacent filter element in such a way that this line end is terminated with high impedance (maximum of the electric field strength) and the other end is coupled to the adjacent filter element or the em or output gate of the bandpass in such a way that the line end is terminated with low impedance (current maximum at the line end), and at the low impedance end of the Main resonator a pair of blocking resonators is electrically or galvanically coupled.
• impedance-symmetrical and impedance-asymmetrical filter elements are to be understood in such a way that with an impedance-symmetrical filter element when the input and output gates are connected with the same terminating resistance, the maximum values of the power transmission factor reach negligible losses , while with the transmission-asymmetrical filter element, complete power transmission can only be achieved for highly asymmetrical gate resistors.
• Figures la to ld show in a schematic manner structures which correspond to the prior art and therefore only in steps Explanation of the basic principle of the structure according to the invention according to figure le serve.
• Fig. La symbolically shows a homogeneous high-frequency line 1, in which this line as a metallic TEM line z. B. as a coaxial line, as a planar line such. B. a microstrip line or strip line or coplanar line, or as a waveguide or as a dielectric line. If the dissipation is neglected, the frequency response of the power transmission factor 2, i.e. the frequency dependence of the ratio of the power P 2 emerging at the reflection-free gate 2 to the power P incident at the gate 1 in the operating frequency range of the line considered, is equal to one regardless of the frequency.
• FIG. 1b schematically shows a structure modified compared to FIG. 1 a, in which two discontinuities 3 are introduced symmetrically into the cable run.
• These discontinuities define a line segment of finite length a, on which electromagnetic natural vibrations occur at those frequencies at which the length a corresponds to an integer multiple of half a line wavelength, and these natural vibrations are characterized by standing waves with nodes and bulges of the electrical and magnetic field strength along the line , where m of the plane of symmetry 4 at the resonance frequency is a node of the electric or magnetic field strength.
• the structure thus created represents a 1-pole bandpass, which is well known in the prior art and which has a maximum due to a frequency response of the power transmission factor 5 1 (damping zero point) is marked at a frequency f 0 .
• the discontinuities delimiting the line piece can technically e.g. B. in In the form of line interruptions or in the form of metallic diaphragms, and it is also well known from the prior art that the frequency bandwidth ⁇ f of the transmission curve can be changed via the strength of the coupling between the supply lines and the ends of the line piece serving as a resonator ,
• FIG. 1 c shows a structure modified from FIG. 1 a, in which a resonance circuit 6 (“blocking resonator”) is coupled to the line, so that the frequency response of the power transmission factor 7 has a transmission zero at the frequency f s .
• This structure represents the construction of a single-pole bandstopper (“notch filter”), which is well known in the prior art.
• FIG. 1d shows a structure modified from FIG. 1c, in which instead of a blocking resonator two blocking resonators 8 with different resonance frequencies are coupled and lead to two transmission zeros at f s ⁇ and f s2 .
• An essential aspect of the invention now consists in forming the structure according to FIG. Le from a combination of the structure according to FIG. 1b and the blocking resonator pair from FIG.
• the line section of finite length forms a resonator, here referred to as the main resonator, which has a node of the electric or magnetic field in the middle.
• An important aspect of the invention is the choice of the coupling between the blocking resonators and the main resonator in such a way that this coupling disappears at the frequency f 0 , this z. B.
• the two blocking resonators thus take on a double function by, on the one hand, realizing two transmission zeros - as in the structure according to FIG.
• the frequency response 10 of the structure according to FIG. Le is thus characterized by a suitable choice of the resonance frequencies and coupling strengths by three transmission maxima (damping zeros) at f x , f 2 and f 3 and two transmission zeros at f s ⁇ and f s2 .
• the frequency position of the transmission zeros is determined by the resonance frequencies of the blocking resonators and the frequency position of the average transmission maximum by the length of the main resonator.
• the position of the two outer transmission maxima can be changed by the coupling strength between the main resonator and the blocking resonators, with an increase in the coupling these frequencies shifting towards the middle frequency.
• the electric field at frequency fo has a node in the plane of symmetry and thus the two blocking resonators must be electrically coupled according to the above design rules, while in the case of magnetic field maxima at the ends, because of the node of the magnetic field , there must be a magnetic coupling.
• the length of the line stub In order to be able to use a magnetic coupling between the blocking resonators and the main resonator in the case of magnetic field maxima at the ends, the length of the line stub must correspond to a full wavelength instead of half a center frequency line wavelength.
• N N g xQ
• M NQ transmission zeros
• An impedance-unbalanced filter element is realized in accordance with the invention by modifying an impedance-symmetrical filter element with a pair of blocking resonators according to FIG. 1e, one of the two discontinuities being brought close to where the blocking resonator is located -Pair is coupled.
• At least one impedance-symmetrical element is added in a cascade of impedance-asymmetrical filter elements.
• the impedance-symmetrical element 5 can be located at one end of the cascade, or it can be inserted centrally (see FIG. 4c).
• the main resonator 1 has a rectangular outer and inner conductor and a length equal to 1.5 times the center frequency wavelength.
• the discontinuities delimiting the line piece are designed in the form of capacitive couplers.
• the blocking resonators 2 are as on Realized short-circuited coaxial line pieces of a length of about a quarter of a line wavelength, which are capacitively coupled to the main resonator.
• FIG. 6 shows a modification of the structure according to FIG. 5, in that the blocking resonators 2 are now galvanically connected to the inner cavity of the main resonator, but are capacitively loaded at the end.
• FIG. 7 shows a structure consisting of two impedance-asymmetrical filter elements and one impedance-symmetrical element, in which one obtains 9 poles and 8 transmission zeros.
• FIG. 8 shows a filter consisting of an impedance-symmetrical filter element with 5 poles and 4 transmission zeros, which is implemented on the basis of rectangular hollow lines for the HIO wave type.
• the main resonator 1 consists of a rectangular waveguide short-circuited at both ends, which has a length at the center frequency corresponding to a waveguide wavelength.
• the 4 blocking resonators 2 are realized in the form of short-circuited 1/4 hollow pieces.
• the coupling to the gates can e.g. B. via a coaxial transition 3.
• FIG. 9 shows an example of an implementation with dielectric resonators in the case of a filter comprising two impedance-symmetrical filter elements, each filter element producing three poles and two transmission zeros, and thus the bandpass filter has a total of 6 poles and 4 transmission zeros.
• Those made of a suitable dielectric material that is to say material with the highest possible dielectric constant, a low loss angle and a low one Temperature coefficients (eg barium titanate zirconate) produced main resonators 1 and blocking resonators 2 are spacers 3, z. B. made of quartz material; positioned to avoid excessive ohmic losses at a sufficient distance from the bottom of the metallic housing 5.
• the dimension of the main resonator is chosen so that it has a natural resonance at fo with the field distribution shown in Fig. 9b, and the dimension of the blocking resonators are chosen so that they resonate at the 4 blocking frequencies fi to f 4 and thereby a field distribution according to Fig. 9c. Because of the spatial field distribution of the main resonator, it does not couple to the resonance fields of the blocking resonators at f 0 . For frequencies other than f 0 , however, a coupling is obtained between the main resonator and the blocking resonators, with the result that an additional 4 natural resonances occur.
• the coupling to the gates can e.g. B. via conductor loops 4.
• the main resonator 5 consists of a dielectric cuboid of length a, which corresponds approximately to a wavelength of the surface wave on the dielectric cuboid. In this way, a field distribution corresponding to FIG. 10b is obtained on the main resonator.
• the 4 blocking resonators 1 to 4 also consist of dielectric cuboids, the individual lengths bl to b4 of which influence the frequency position of the 4 transmission zeros.
• the entire structure of the main dielectric resonator and 4 dielectric blocking resonators realizes 5 natural vibrations.
• the frequency position of the poles can be adjusted via the coupling strength between the main and Resonators are changed.
• the “gaps” filled with air or a dielectric material with a relatively low dielectric number serve to change this coupling strength between the resomators with the widths hi to h 4 .
• planar resonator structures such as, for. B.
• microstrip line structures are used, microstrip line structures made of high-temperature superconductors are also of interest, since they have a high level of idling despite an enormous degree of miniaturization.
• FIG. 11 shows the well-known structure of a microstrip line resonator 3, which at its ends is capacitively connected to the leads 4, 5 is coupled.
• the frequency response of the power transmission factor 6 shows a maximum at the frequency f 0 and the width of this maximum can be changed via the strength of the coupling at the line ends (discontinuities).
• FIG. 11b shows how an impedance-asymmetrical filter element according to the invention can be realized in microstrip line technology.
• a T-shaped conductor structure is used, in which the length of the individual arms is approximately a quarter Line wavelength corresponds to the center frequency, whereby a well-defined asymmetry in the length or width of the side arms 3 is necessary for the function.
• the side arms represent a simple implementation of the blocking resonators, the blocking frequencies being influenced over the length of the arms. Together with the third arm, the side arms form e structures, which resonate at two different frequencies and thus the T-structure represents a special form of a dual-mode resonator.
• the output gate can be capacitively connected to the T in the manner shown in FIG. 11b Structure to be coupled.
• the frequency response 6 of the two-port thus created is characterized by two transmission maxima and two transmission zeros, the absolute value of the transmission maximum being able to be far below one due to the asymmetry. For this reason, an individual asymmetrical filter element - in contrast to the impedance-symmetrical filter element - is not yet a usable bandpass filter.
• this microstrip line structure can also be modified in a variety of ways, e.g. B. by using inhomogeneous pipe pieces of variable width.
• FIG. 12 shows an example of how 4 impedance-asymmetrical filter elements 1 and a conventional half-wave resonator 2 can be used to form a 9-pole filter with 8 transmission zeros.
• the resonator 2 in the cascade transforms the impedance at gate 2 (e.g. 50 ohms) to the low impedance level at the coupling point to the branching point of the T-shaped resonators.
• the dimensioning of the parameters of each Filter elements, here z. B. done so that a Cauer characteristic is achieved for the frequency response.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)
• Filters And Equalizers (AREA)

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• 1999
  • 1999-08-31 DE DE19941311A patent/DE19941311C1/de not_active Expired - Fee Related
• 2000
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  • 2000-08-26 AT AT00960529T patent/ATE233956T1/de not_active IP Right Cessation
  • 2000-08-26 JP JP2001520502A patent/JP2003508948A/ja active Pending
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  • 2000-08-26 WO PCT/EP2000/008333 patent/WO2001017057A1/fr active IP Right Grant
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  • 2000-08-26 ES ES00960529T patent/ES2191642T3/es not_active Expired - Lifetime
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