EP0901692A1

EP0901692A1 - Method of tuning planar superconductive filters

Info

Publication number: EP0901692A1
Application number: EP97922897A
Authority: EP
Inventors: Werner GRÜENWALD; Christian Neumann; Matthias Klauda; Claus Schmidt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1996-05-28
Filing date: 1997-05-09
Publication date: 1999-03-17
Anticipated expiration: 2017-05-09
Also published as: WO1997045888A1; DE59704975D1; DE19621335A1; EP0901692B1

Abstract

The invention concerns a method of tuning planar superconductive filters by means of a vertically adjustable housing cover which enables the mid-frequency of the band-pass filter to be set. In this way, the filters can be tuned considerably more easily. The invention also concerns the construction of a filter bank for multiplex applications.

Description

Process for tuning planar superconducting filters

State of the art

The invention is based on a method for tuning planar superconducting filters according to the type of the independent claim.

From EP 05 22 515 AI a method is known to detune a planar superconducting filter with a single resonator. The planar filter to be tuned consists of a substrate with a superconductor layer on the underside, which serves as a ground line. On the top there is a micro structure, also made of superconducting material, which has a conductor for capacitive coupling of the

High-frequency signal, a resonator, and a line for capacitive coupling of the signal comprises. The resonator is an approximately circular planar microstructure, the lateral dimensions of which determine its resonance properties. Furthermore, the effective dielectric function of the surroundings of the resonator determines its resonance properties. The imaginary part of the effective dielectric function causes the filter losses, its real part influences the position of the resonance frequency. The filter is located in a housing, in the lid of which at least one with a thread provided through hole is provided. This rotates a screw such that the screw head is outside the housing and the threaded end of the screw is immersed in the electric field of the microwave or millimeter wave propagating in the filter. In order to minimize the losses, the attachment of a superconducting plate with approximately the same diameter as the thread of the screw on the screw tip is proposed.

In a filter with several resonators, a screw located above a resonator influences its resonance frequency in a first approximation. A screw that dips into the space between two adjacent resonators primarily affects the coupling between these two resonators. The tuning method proposed in EP 05 22 515 AI for a single resonator is suitable for the production of filters with very low losses, but the tuning of more complex filters with a larger number of resonators is extremely time-consuming due to the large number of degrees of freedom. This is known to the person skilled in the art.

Furthermore, WO 94/28592, in particular FIG. 12, shows a planar bandpass filter

High-temperature superconductor base known in microstrip technology. There is a superconductor layer on the underside of a carrier substrate, which serves as a ground line. On the top there is a microstructure, also made of superconducting material, which comprises a conductor for the capacitive coupling of the high-frequency signal, several resonators, and a line for the capacitive coupling out of the signal. The resonator is a strip conductor of approximately rectangular shape, the lateral dimensions of which resonate determine. In WO 94/28591, the carrier substrate consists of a layer structure which contains at least one ferroelectric or antiferroelectric layer. By applying a voltage to this ferroelectric or antiferroelectric layer, its dielectric function can be changed significantly, and thus also the dielectric function of the environment of the planar filter. The resonance characteristic of the filter can thus also be changed, but only integrally, that is to say in an approximately identical manner for all

Resonators that form the filter. This process is accompanied by an increase in losses.

Advantages of the invention

The method according to the invention with the characterizing features of the independent claim has the advantage that the coordination is significantly less complex and still allows to produce filters with low losses. Another advantage is that, due to the shorter time required for the tuning, the manufacturing costs of a fully tuned filter turn out to be significantly lower, since the time required for tuning represents a significant proportion of the manufacturing costs.

The measures listed in the dependent claims are advantageous developments and

Improvements to the method specified in the independent claim possible. It is particularly advantageous to provide a displaceable wall on the housing, since this means that all resonance frequencies of all resonators are shifted evenly and only a slight adjustment effort is required fewer screws are required to couple the individual resonators.

It is also particularly advantageous to provide a double-walled housing wall with a lowerable inner cover, since the housing can thus be sealed more easily.

Furthermore, it is particularly advantageous to move this inner cover by means of piezotranslators, since this method of adjustment can also be carried out at operating temperature (generally 77 Kelvin) and, if necessary, also in a refrigerant bath. Another advantage is that, due to the electrical control of the resonance shift, this method is compatible with electrical control loops.

Furthermore, it is particularly advantageous to provide the inside of the housing cover with a conductive plate of a precisely defined thickness, since this method already provides a roughly pre-adjusted filter when the filter is installed. Another advantage is that

Manufacture of a suitable set of plates, which are very inexpensive to manufacture, a set of filters with slightly different resonance frequencies can be made without producing different superconductor microstructures, for which an incomparably more expensive set of different masks would be required.

Finally, it is particularly advantageous to accommodate several filters of the same type in a housing with a stepped cover, since a filter bank for frequency division multiplex applications can be obtained very inexpensively in this way. Drawing

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. Show it

1 shows the perspective view of a filter in a cut-open housing which is provided with a height-adjustable cover,

FIG. 2 shows a transmission curve of a filter according to the invention,

FIG. 3 shows a filter installed in a housing, which has an inner cover that can be lowered from the cover,

FIG. 4 shows a filter which is built into a housing and which has an inner cover which can be lowered relative to the cover by means of piezotranslators,

Figure 5 shows a filter installed in a housing which is provided with plates on the inside of the lid and

Figure 6 is a filter bank, on the housing cover a stepped plate is attached.

Description of the invention

Figure 1 shows a planar filter in

Microstrip construction in one housing. The planar filter consists of a dielectric substrate (1), which has a superconductor, preferably a high temperature superconductor is coated. This layer forms the ground line (2). A microstructure, also made of superconducting material, consisting of an input line (3), is applied to the top of the dielectric substrate (1).

Resonators (4,5,6) and an output line (7). This planar superconducting filter is installed in a housing consisting of a base plate (10), a housing wall (11) and a cover (12). The cover (12) is fastened to the housing wall (11) by means of two screws (13, 14). In the following text, the terms housing wall or wall are also used as a collective term for cover, base plate and wall. In the cover (12), perpendicular to the line (30), there is a coupling screw (20), the threaded end of which protrudes from the inside of the housing. The line (30) runs between the resonators (5,6); Sectional drawings in the following figures show sections along a plane which contains this line and runs perpendicular to the surface of the substrate (1).

An incoming millimeter or microwave is coupled to the series of resonators (4,5,6) via the input conductor (3). The filtered signal is available on the capacitively coupled output conductor (7). The planar filter shown in FIG. 1 is a bandpass filter, in which only microwaves or millimeter waves (hereinafter also referred to collectively as high-frequency waves) with a frequency that corresponds to the natural frequency of the resonators (4, 5, 6) between the input conductors (3) and output conductor (7) are transmitted. Suitable filtering can also be used to implement other types of filters, in particular band-stop filters, low-pass filters or high-pass filters, to which the method according to the invention can also be applied. The cover (12) is by means of the screws (13,14) attached to the housing wall (11). In addition, these screws (13, 14) are used to adjust the height of the cover. This is done by loosening the screws (13, 14) and holding up the cover (12) by a lock nut (15) placed on the screws (13, 14). The lock nut placed on the screw (14) is covered by the cover (12) in FIG. 1. By lowering the cover (12), the resonance frequencies of all resonators (4, 5, 6) and thus the transmission band of the filter are shifted to higher frequencies, raising the cover acts counter to this. The characteristic of such a filter, albeit with seven resonators, for two different layers of the cover is shown in FIG.

The coupling between the individual resonators determines the spectral fine structure within the transmission band. An example of this very weak spectral fine structure is marked with an arrow in FIG. This coupling is influenced by the coupling screw (20). The threaded end of the coupling screw is immersed both in the electrical field of the resonator (5) and in the electrical field of the resonator (6) and thus serves as a double capacitive coupling between the resonators (5) and (6). A more developed coupling, which in the embodiment chosen here is a further screwed in

Corresponds to the screw, smoothes the fine structure within the transmission belt. With stronger coupling, the transmission band is also spread out, so that the fine adjustment has the aim of simultaneously adapting the bandwidth and spectral fine structure of the filter to the intended use. This fine adjustment of the spectral transmission characteristic will generally be carried out after the spectral position of the entire transmission band has been fixed by the lowerable cover. A second exemplary embodiment according to the invention is shown in FIG. FIG. 3 shows a section through a filter in a housing along a section line (30) (see FIG. 1). Components that are the same or function the same as in FIG. 1 have been provided with the same reference number. On the underside (2) of a dielectric substrate (1) there is a superconducting layer (2) which functions as a ground conductor. The resonators of the filter lie outside the section plane and are therefore not visible in FIG. 3. The filter is installed in a housing with a base plate (10) and housing wall (11), the structural design of which ensures that the filter element is securely fixed. However, those skilled in the art are also alternative methods of attachment, such as. B. gluing, screws, staples, etc., obviously. The housing also has a cover (12) which is provided with holes (50, 52, 53). Inside the housing, parallel to the cover (12), is the inner cover (40), which has a bore (51) aligned with the bore (50), which is provided with a thread. Furthermore, two threaded bolts (41, 42) are attached to the cover (40), such that they protrude outwards through the holes (52, 53) in the cover (12), and a seal (45) which seals the inner cover (40). seals against the housing wall. Nuts (44.45) are screwed onto the threaded bolt (41.42). Springs (16) are glued to the outside of the cover in such a way that their resilient end touches the end of the threaded bolts (41, 42) and exerts an axial force on them in the direction of the filter. Through the threaded hole (51) is one

Coupling screw (20) screwed in. Securing lugs (15) are provided on the housing walls (11).

The nuts (44,45) located on the threaded bolts (41,42) serve together with those on the threaded bolts pressing springs (16) for setting and fixing a distance between the inner cover (40) and the cover (12). By loosening the lock nuts (44, 45), the inner cover (40) is lowered by the spring pressure and thus the frequency of the transmission band of the filter is increased. The securing lugs (15) protect the superconducting microstructure on the top of the substrate against damage by an erroneously detached inner cover (40). The coupling screw (20) makes it possible to influence the coupling between the individual resonators, and thus the spectral fine structure within the transmission band. The seal (45) and the fact that the hole (51) is threaded results in a relatively tight housing. Nevertheless, it may U. be useful to provide the hole (50) instead of the hole (51) with a thread for adjusting the coupling screw (20) to separate the coupling between resonators and the frequency detuning of the resonators. A screw mechanism for adjusting the height of the inner cover (40) other than that shown here is also conceivable.

In particular, high-precision inserts, which have small installation dimensions and can be integrated into the cover, are also conceivable here.

An electrically controllable method of lowering the inner cover in order to tune the filter is shown in the further exemplary embodiment in FIG. 4. Again, there is a planar filter applied to a dielectric substrate (1), of which only the superconducting ground conductor (2) is visible in the sectional drawing shown, in a housing which consists of a base plate (10), a housing wall (11) and a Cover (12) exists. The filter and housing are cut along the same cutting line as the device in Fig. 3. The same or functionally identical components as in the previous figures have been given the same reference numerals. On the inside of the cover (12), two piezotranslators (60) are attached, which in turn are connected to the inside cover (40). Inner cover (40) and cover (12) have two coaxial bores (51, 50), of which the bore (51) is threaded and the bore (50) is provided with an electrically insulating guide bush (61). A coupling screw (20) is located in the bore (51).

The raising and lowering of the inner cover, which influences the filter characteristics in the same way as in the previous example, is done in this example by applying a voltage to the piezo transformer (s) (60). In the present embodiment, the

Coupling screw (20) attached to the inner cover and not to the outer cover. An obvious solution for applying a voltage to the piezo translator (60) is therefore to apply a voltage between the cover (12) and coupling screw (20). There is also the possibility of

Disconnect the voltage supply to the piezotranslators (60) using two conductor wires; in this case there is also the possibility of anchoring the coupling screw (20) in the cover (12) instead of in the intermediate cover (40) in order to largely separate the adjustment of the spectral position of the transmission band on the one hand and its spectral shape on the other hand. One possible application of this exemplary embodiment of the invention disclosed here is to combine the electrically controlled tuning of the filter with a control and regulating circuit in order to compensate for drift phenomena, for example.

The sectional drawing in FIG. 5 shows a further preferred exemplary embodiment. The section is carried out along the section line shown in FIG. 1; same or functionally identical components as in the previous figures are provided with the same reference numerals. Again, there is a filter, consisting of a ground conductor (2), applied to a dielectric substrate (1), and a resonator (not visible in FIG. 5) in a housing, consisting of a base plate (10), housing wall (11) and cover (12 ) , built-in. A coupling screw (20) is screwed into a threaded hole (50). A conductive plate (70) is attached to the inside of the cover (12).

In this exemplary embodiment, the spectral position of the filter band is selected by selecting a plate (70) with the appropriate thickness and attaching it to the inside of the cover (12). Again, the coupling screw (20) can be used to influence the spectral

Fine structure of the filter belt can be used. The change in the spectral position of the transmission band is no longer possible after the assembly of the housing without opening the housing again, however, a pretuning can be made in this way with very simple means, which then only with the aid of the coupling screws (20) Detail needs to be corrected. It is also possible to use a set of selected plates (70) to produce a set of filters from the same superconductor microstructure, the transmission characteristics of which differ in a precisely defined manner.

FIG. 6 shows the cross section through a filter bank in which there are four identical planar filters (80), produced with identical masks on identical ones

Substrates, starting from identical superconductor layers on both sides. The housing consists of a base plate (10), a housing wall (11) and a cover (12). A step plate (72) is attached to the inside of the cover (12). Due to the different distances between the planar filters (80) and the surface of the step plate (72) facing them, the spectral position of the transmission frequencies of the channels realized by the individual planar filters is slightly detuned from one another without changing the spectral fine structure. In this way, a multi-channel filter bank can be built with very simple means and bypassing the production of several masks. If necessary and / or desired, additional screws for fine tuning can also be provided in this implementation example.

In the previous exemplary embodiments, the housing cover was used to represent other housing components which are sufficiently close to the planar filter so that they interact with the electrical field of the high-frequency wave propagating through the filter structure. Possible modifications of the invention consist in making one or more side walls and / or the floor slidable in the sense mentioned above. It also seems conceivable to implement the coupling screws (20) and the sliding cover on different surfaces, for example to attach the coupling screws (20) to a side wall coaxially to the line (30) shown in FIG. 1, and which are parallel to the substrate (1) running housing surface facing (that is, the surface with the resonators) as a sliding cover in the sense mentioned above.

In the above exemplary embodiments, coupling screws (20), which protrude into the half-space between two resonators, were used if, in addition to the displacement of the transmission band, the fine structure of the transmission band is changed by the displaceable housing wall should. It is also conceivable, in addition to the lowerable housing cover, to provide one or more tuning screws in the field space above a single resonator. It is then possible to move the entire transmission band integrally by moving the housing wall, and in addition, for example by moving the resonance of a single resonator, to design the filter to be narrowband or broadband.

Claims

Expectations

1. A method for tuning planar superconducting filters for millimeter waves or microwaves with multiple resonators, the filter being arranged in a housing, and a conductive element which is sufficiently close to the filter so that it matches the electric field of the millimeter waves or Microwaves can interact, is shifted relative to the filter, characterized in that the conductive element extends over several resonators.

2. The method according to claim 1, characterized in that at least one housing wall is moved.

3. The method according to claim 1, characterized in that the part facing the resonators of a double-walled housing wall is displaced relative to the filter.

4. The method according to claim 3, characterized in that the displacement is effected by turning a screw or a nut.

5. The method according to claim 3, characterized in that the displacement is effected by piezotranslators.

6. The method according to claim 1, characterized in that a conductive plate with the necessary thickness for the desired detuning is attached to at least one inner wall of the housing.

7. filter bank consisting of at least two planar superconducting filters for millimeter waves or microwaves, installed in a housing, characterized in that on the inside of the cover a conductive step plate in sufficient proximity, so that the filter facing surface of the step plate with the electrical field of the millimeter waves or Microwaves can interact, is appropriate.