SE507751C2 - Device and method of filtering signals - Google Patents

Abstract

The present invention relates to a superconducting notch or band reject filter arrangement (10) which comprises a superconducting dielectric resonator (11) and a waveguide arrangement (15) comprising a microstrip line to which the resonator is connected. The resonator (11) is a parallel-plate resonator with a chip of a non-linear dielectric material (12) on which superconductors (13a, 13b) are arranged and the waveguide arrangement comprises contact means or a coupling means (18), the resonator (11) being connected to said contact means (18) of the waveguide arrangement in such a way that electric contact is provided and the filter arrangement is frequency tuneable. Through said arrangement the insertion losses are low.

Description

10 l5 20 25 30 507 751 In addition, such filters are large. In “High-Temperature Superconducting Microwave Devices ”by Shen, Artech House, 1994 discusses the use of high temperature superconductors to provide new opportunities to reduce the size of, and to improve the performance of ndkrovåg components, for example filter.

European patent application EP-Af0 567 407 shows superconductivity notch filter with a fixed frequency where half-wavelength, high temperature superconducting microstrip resonators are parallel connected to the high temperature superconducting main microstrip conductor.

The substrates of the resonators have dielectric constants of about 10- At frequencies between 1-3 GHz. The length. on the filters is then about 2-6 cm; the filters are thus very large and so are they expensive.

Some communication systems require tunable (interchangeable) notches filter instead of notch filter for a fixed frequency for example to be able to increase the flexibility of the system. US-A-4,835,498 discloses one single dielectric resonator. The resonator is passive and not itself tunable. To achieve tunability, separate ones are needed tuning means, such as a diode or the like. In other words, required a separate biasing circuit. This makes the device.necessarily In addition, the device becomes complex and its WO 93/00720 illustrates a superconductivity becomes significantly larger. performance is too low. notch filter with a microstrip conductor that is not tunable in itself. IN in this case, optical means were used to effect tuning.

These optical means utilize semiconductor crystals in superconducting microstrip ring resonators connected to the superconducting the main microstrip. However, the dimensions of these devices are large and in addition the frequency tuning range is far too small. Both of these documents show passive resonators and they need special biasing networks and additional tuners that are connected 10 15 20 25 30 507 751 to the main microstrip conductor in the same manner. The resonators can not be in mechanical or electrical contact with the main microstrip conductor.

If there is no connection, you also do not have a filter. MAN has also concluded that microwave devices can be made less about non-linear dielectric materials with a high dielectric (STO) is plated WO 94/13028 discloses strontium titanate with (YBCO). constant such as, for example superconductors such as Y-Ba-Cu-O use of thin single crystalline dielectric films in combination with high temperature superconductors which as such give rise to for in addition can such high microwave losses and devices are not made small enough.

DESCRIPTION OF THE INVENTION What is needed, therefore, is a superconducting notch filter device such as has low input losses, small dimensions and is adjustable.

A device such as. is tunable within a wide range frequency range. In addition, a device that is inexpensive and easy to produce. In addition, a device having a pile is needed performance discussed above, has low losses, especially low microwave losses (in the case of microwaves); it can also be used for millimeter waves.

A method for filtering incoming signals, for example to communication systems operating at high frequencies are needed through receiving devices in a multichannel microwave which intermittent and interfering signals can be extinguished an efficient and reliable way.

Therefore, a superconducting notch filter device comprising a resonator as arranged on a microstrip conductor where the resonator is one parallel plane resonator with a chip of a non-linear dielectric material on which superconductors are arranged.

The resonator is connected to a connection means for one lO l5 20 25 30 507 751 ndkrostri leader or to a band on the ndkrostri leader on one way to an ohmic contact electrically such is achieved. The device is especially tunable, even more special to it through application of a dielectric DC biasing voltage non-linear whose dielectric constant can change. In a in particular embodiments, a DC voltage is applied to normal conductors which may be arranged on the superconductors arranged on means of contact, arranged to provide dielectric In an advantageous resonator dielectric. It is also beneficial designated coupling agents, contact between the resonator and the microstrip conductor. the means of contact formed embodiment is by the microstrip conductor central band.

In one, a resonator comprises one special embodiments rectangular (or of some other shape) chip that is so oriented in relation to the microstrip conductor that the magnetic field lines for the microtrip conductor and the resonator substantially coincide on one such that maximum inductive coupling is achieved.

The inductive connection is controlled or given especially by the relationship between the resonator and the microstrip conductor. Even more special is given the strength of the inductive coupling of the width of the central microstrips. To get the desired strength. on the clutch can the width is thus given the value which gives the desired coupling.

According to a particular embodiment, at least one has section of the lower plate in the parallel-plane resonator and / or the microstrip connectors, for example the central conductor, a first width which is less than a second width to provide one increased inductive connection. 10 15 20 25 5 According to an exemplary embodiment, the resonator is a dual mode resonator or even more specifically it is one multimode resonator.

However, dual mode operation is advantageously provided by the introduction of an asymmetry into the resonator. This asymmetry can for example, consist of a cut - off corner or a protrusion or something else. In accordance with another embodiment, the resonator be arranged so that it forms an angle with the main microstrip conductor. The angle can, for example, assume a value of about 45 °.

In accordance with yet another embodiment, the waveguide device comprises a coplanar waveguide.

The coupling strength, is controlled by or given by the 'width of the central the conductor and of the coplanar waveguide slots. (which all embodiment) by applying a DC biasing voltage which The reconciliation is advantageously achieved can be applied between the upper plate of the resonator and the coupling means, for example the central conductor of the microstrip conductor.

In accordance with an advantageous embodiment, the area of -1 the resonator has a size of between approximately 1 nmf-1 cm However, these values are given for illustrative purposes only, the resonator may also have other proportions, less as well as something major. a procedure to one Also specified for filtering signals incoming, for example, receiving device in one multi-channel communication systems or the like. The procedure comprises the steps of: arranging a filter on the receiving device input side, which filter comprises a parallel plane resonator 10 15 25 30 507 751 comprising a non-linear dielectric substrate on which superconducting conditions are arranged and which is arranged on one waveguide, for example a microstrip conductor. The resonator and the guide device is electrically connected in series by use of how the resonator and of coupling agent. The coupling strength is given the coupling means are arranged in relation to each other. A DC- biasing voltage is applied to the resonator and the coupling means for frequency tuning. The steps are performed so that intermittently interfering signals can be extinguished.

It is, among other things, an advantage of the invention that it is possible to do notch filters that have dimensions that are significantly smaller than for notch filter. It is also an advantage that: hitherto known the frequency tuning range is wide.

BRIEF DESCRIPTION OF THE FIGURES The invention will be further described in one of the following non-limiting manner with reference to the accompanying figures in which: FIG. 1 illustrates an example of a parallel-plane resonator, Fig. 2 schematically illustrates a first embodiment of a tunable notch microstrip filter, Fig. 3 is a cross-section of the notch filter of Fig. 2, FIG. 4 illustrates an equivalent circuit to the notch filter of FIG 2, Fig. 5 is a diagram illustrating the center frequency temperature dependent for a special notch filter, 10 15 20 25 30 507 751 7 Fig. 6a schematically illustrates a cross section of a second exemplary embodiment of a notch filter, Fig. 6b is a longitudinal cross-section of the lower plate in the resonator, Fig. 6c is a longitudinal cross-section of the central one the microstrip conductor in the filter according to Figure Ga, Fig. 7 illustrates an embodiment of a two-pole notch filter, Fig. 8 is a further embodiment of a two-pole notch filter, and Fig. 9 schematically illustrates a coplanar waveguide notch filter.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the invention, a resonator is arranged on a guidance device. Figure 1 shows a first example of a resonator that can be used. The resonator 11 comprises a dielectric 12 i in the form of a rectangular chip of a non-linear dielectric on both sides of which are thin high temperature superconducting films HTS 13a, l3b are arranged. The superconducting films or plates l3a, l3b may advantageously be partially or completely covered by normal leading films 14, of 'Au thus forming ohmic with an advantageous 14 for example contacts for DC biasing. According In the exemplary embodiment, the dielectric material consists of a non- linear dielectric bulk material because for bulk material is the microwave losses are lower and the dielectric constant is higher than, for example, for thin dielectric films. Microwave losses for example, strontium titanate, hereinafter referred to as STO is close to the minimum at the temperature for liquid nitrogen, Nhq which 10 15 20 30 507 751 discussed in LaAlO¿, NdGaO @ ”Dielectric properties of single crystals of ZU¿O @ SrTiO @ and MgO at cryogenic temperatures ”, 1994, of Krupka et al., in IEEE Trans. Vol. 42, pages 1886-1890. 2000 Microwave Theory Techn., The dielectric constant for STO is around Nnq strongly dependent on at the temperature of and it is the temperature and of applied electric DC fields. This is discussed in ”L GHz tunable resonator on bulk single crystal SrTiO3 plated with YBa fl1 nOk_ films ”, Lett., 1995, Vol. 31, no 8, p. 654-656. by O. Vendik in Electron.

Because the dielectric constant is extreme high is the wavelength of a microwave transmission conductor based on STO at the temperature of Nnq in the frequency band 1-3 GHz about 0.2-0.6 cm. The superconducting transition temperature TC for HTS such as for example YBCO is significantly above the temperature for Nhq and it is also well known that HTS films grown on STO substrates have a low surface resistance which is discussed in the article quoted above by Shen.

The resonator may advantageously consist of a non-linear dielectric bulk material 12 for example of STO which is covered by HTS films of YBCO. Of course, it is also possible to for example, do the resonators in other ways, but this relates to a special advantageous execution. l3a, dielectric chip 12 to take into account mechanical tolerances improved The superconducting films or * plates 13b in the parallel plane resonator has been made slightly smaller than that and to achieve an ability. to control the resonant frequency. The thickness of the superconducting plates l3a, 13b exceeds the London penetration depth, where the penetration depth is defined as the depth at which the field has decreased to l / e of the value of the surface.

Figure 2 shows a first embodiment of a tunable notch filter 10 in accordance with the invention. The resonator 11 in Figure 1 waveguide device 15 in the form of a this is arranged on a microstrip conductor. The resonator 11 is in exemplary embodiment connected to or connected to the central conductor 18 of 10 15 20 25 30 507 751 the microstrip conductor 15 where said central conductor 18 includes the contact means or the coupling means which cause ohmic contact ll and The microstrip conductor 15 comprises a subsrat between the lower plate 13b of the parallel plane resonator the microstrip conductor 15. for example of Al or some other known dielectric for waveguide. The ground plane 17 consists, for example, of Cu, Au or something other similar that has normal conductivity. However, in a very advantageous embodiment the ground plane 17 and the central director 18 of HTS films. Parallel plane resonator chip 11 are so arranged in relation to the microstrip conductor 15 that they the magnetic field lines of the microstrip 18 and the resonator 11 essentially coincides which ensures one (compare figure 3) high degree of inductive coupling, or exactly precise maximum inductive coupling. The width of the central microstrip 18 determines the coupling strength between the resonator 11 and the microstrip conductor 15 and thus, the coupling strength can be controlled by selecting the appropriate width.

The width may in an advantageous embodiment be approximately in the order of magnitude between 0.5-1 mm but it can also be smaller or greater. Thus, in this way, a series resonant circuit is introduced in the microstrip conductor 15 which then acts as a band-stop filter, i.e. a notch filter for incoming microwave signals. Coupling means 19, 19 are provided by which a DC biasing voltage can be applied on between the microstrip conductor and the upper plate 13a in parallel plane resonator 11. In this way, electrical tuning and the DC biasing voltage applied to the non- linear dielectric 12 changes the dielectric constant of this and thereby the resonant frequency of the parallel plane resonator 11.

In accordance with another embodiment not discussed further here, a temperature controlled tuning can be applied either in addition to electrical tuning or as an alternative thereto. 10 15 20 25 30 507 751 10 Optical or mechanical (eg via piezoelectric means) reconciliation can of course also be used.

Figure 3 is a cross-sectional view of the notch filter 10 as illustrated in figure 2. It shows how the resonator 11 is arranged on the central the microstrip 18 of the microstrip conductor 15. H denotes the magnetic ones the field lines of the resonator and the microstrip conductor. Sàsom discussed above, the field lines essentially coincide, which gives a high degree of coupling between the resonator 11 and the microstrip conductor 15.

Figure 4 schematically shows an equivalent circuit for the notch filter 10 as illustrated in Figures 2 and 3 above. Z0 denotes the impedance for the microstrip conductor while the dashed line is the circuit representation of the resonator 11. In a special exemplary embodiment, the resonator is a STO resonator plated with YBCO films as discussed above and dielectrics have in this special embodiments dimensions 2.5> <2.5 x 0.5 mm3. IN this exemplary embodiment comprises the waveguide device a 50-ohm copper microstrip on a 0.5 mm. aluminum substrate. Of course is this is just an example and other materials can be used, the dimensions may be different, etc. In addition, the resonator needs not be rectangular but may also take other forms, square, oval, etc. However, Figure 5 shows a diagram above the temperature dependence of the center frequency of a notch filter that has above-mentioned dimensions and where no biasing voltage is applied.

Figure 6a shows an alternative embodiment of a notch filter 20. that also. in this case consists of a non- bulk material 22 23b which in turn are covered by normal A resonator 21, linear dielectrically plated with barrel superconducting films 23a, conductive layers 24a, 24b ndchrostrip conductor 25. The microstrip conductor 25 consists of a substrate for example, by Au, is arranged on a 10 15 20 25 30 507 751 ll for example by Al. On one of its surfaces is, for example, one copper microstrip 27 arranged while on the other side of the substrate is a central microstrip 28 is provided. The central. microstrips 28 forms the contact means or the connecting means between the resonator 21 and the microstrip conductor 25. In this embodiment, one is provided 23b¿ i den the resonator plate 23b having a smaller width than a first section 23bh inductive load through, a second section lower The microstrip conductor 28 is also provided with a second section 28b whose width is less than the width of a first section 28a.

Figures 6b and 6c are longitudinal views seen from above of it the lower plate in the resonator and the microstrip conductor, respectively, there the device illustrated in Figure 6a indicates sections 23b¿ and 28b each having a smaller width.

Figure 7 shows a very schematic two-pole notch filter. A resonator 31 (for example, as discussed with reference to earlier embodiment) is arranged on a 1nicrostrip conductor 35. One of the corners of the upper superconducting film 33a are cut off; this give dielectric.

Because one of the horns of the Upper Superconducting Film 33a is thus an asymmetry in the resonator. 32 indicates cut off, it is achieved that the resonator 31 can operate in two modes.

Thus, the width of the barrier band and its shorts can be adapted to them current needs. shows another In this case Figure 8 notch filter 40. exemplary embodiment of a two-pole is a resonator 41 (compare above) arranged on the microstrip conductor 45 in such a way that it forms an_ angle with. the microstrip conductor. In this particular case form the parallel plane resonator 41 at an angle of 45 ° with the main microstrip conductor. Since an asymmetry is introduced, the resonator also works in this case in two modes. The angle needs 10 15 20 25 30 507 751 12 of course not be 45 ° but it can assume higher as well as lower values; in principle it can be anything except 90 °.

The invention can in principle also be applied to multimode filters such as for example, working in three modes. Such a device is illustrated in it was simultaneously submitted methods Swedish patent application “Arrangements and relating to multiplexing / switching "by the same applicant, the contents of which are incorporated herein.

Figure 9 schematically illustrates yet another embodiments comprising a tunable coplanar waveguide (CPW) notch filter 50 that can also work in two modes. One superconducting parallel plane resonator 51 is connected to it central conductor 58 on a coplanar waveguide (CPW) 55 to enable a greater degree of freedom in terms of design.

Coupling strength and path impedance of the coupler guide 55 is given by the width of the central conductor 58 and the openings 59 in CPW en. In general, the breadth of the central leader can assume them values previously discussed with reference to Figure 2 (as also applies ç utför a the other embodiments) but i. this cases, the flexibility is even higher. The width is generally selected depending on the substrate thickness.

The invention is not limited to the embodiments shown for example, it does not have to be fall can without other materials can be used, a dielectric bulk material, in some also thin dielectric materials are used. In addition, the shape of the resonator can be of different kinds as well as the guide devices can assume one not necessarily be one number of different shapes and it needs central conductor of microstrip conductors forming the coupling means.

Claims (28)

(D 10 15 20 25 30 507 751 13 PATENT CLAIMS A superconducting notch or bandpass filter device (10; 20; 30; 40; 50) comprising a superconducting dielectric resonator (11; 21; 3l; 41; 51) and a waveguide device (15; 25; 35; 45; 55) comprising a microstrip conductor to which the resonator is connected, characterized in that the resonator (11; 21; 31; 4I; 51) is a parallel plane resonator with (12; 22; 32) arranged on it and that a chip of a non-linear dielectric material which superconductor (13a, 13b; 23a, 23b; 33a) is the waveguide device comprises a ndchrostrip conductor to which one of the plates of the parallel plane resonator is connected via contact means or coupling means (18; 28; 58), where the resonator (11; 21; 31; 41); 51 are connected to said contact means (18; 28; 58) of the waveguide device in such a way that electrical contact is provided and that the filter device is frequency tunable. Superconducting filter device (10; 20; 30; 40; 50) according to claim 1, characterized in that it is electrically descended. A superconducting filter device according to claim 2, characterized in that a DC biasing voltage via the connecting means (19, 19) is applied directly or indirectly to the non-linear dielectric to change its dielectric constant. 4. A superconducting filter device according to claim 3, characterized in that normal conductors are arranged on the outer sides of the resonator, i.e. on the superconductors and that a DC biasing voltage is applied thereto. A superconducting filter device according to any one of the preceding claims, characterized in that the contact means (18; 28; 58) consist of a central strip of the microstrip conductor and that the resonator is connected to said central strip. A superconducting notch filter device according to any one of the preceding claims, wherein (ll; 2l; 3l; 4l; 5l) the resonator is a substantially rectangular chip. 7. A superconducting notch filter device according to claim 6, characterized in that the resonator chip is so oriented in relation to the microstrip conductor that maximum inductive coupling is achieved. A superconducting notch filter device according to claim 7, characterized in that the resonator chip is so oriented relative to the microstrip conductor (15; 25) that the magnetic field lines of the microstrip and the resonators substantially coincide. A superconducting notch filter device according to any one of the preceding claims, characterized by the resonator and the coupling between the relationship that the inductive between the resonator and the microstrip conductor is given by the microstrip conductor and that it is given by the relationship between its physical dimensions. A superconducting notch filter device according to claim 9, characterized in that the strength of that contact means, (18; 28; 58). The inductive connection is determined by the width of, for example, the central microstrip conductor ll. Superconducting notch filter device according to any one of the preceding claims, characterized in that in order to increase the inductive coupling between the resonator (25) the parallel plane resonator (21) and (23b) of the microstrip connection means comprise the lower and / or (23b2; 28b) than the width of a respective first section (23b1.28a). the microstrip conductor plate each has a second section that has a width that is smaller Superconducting notch filter device (30; 40) according to one of the preceding claims, characterized in that (31; 4l) the resonator is a double-mode operating resonator and the filter device consists of a two-pole filter. A superconducting notch filter device (30; 40) according to claim 12, characterized in that the resonator (3l; 4l) has dual mode operation. includes an asymmetry to achieve A superconducting notch filter device (30) according to claim 13, characterized in that the asymmetry consists of a cut-off corner of a plate (32a) of the resonator, a projecting part or the like. 10 15 20 25 30 507 751 16 A superconducting notch filter device (40) according to claim 12, characterized in that the resonator (41) is arranged to form an angle with the main microstrip conductor (45). The superconducting notch filter device according to claim 15, characterized in that the resonator (41) forms an angle of about 45 ° with the main microstrip conductor (45). A superconducting notch filter device (50) according to any one of claims 1-16, characterized in that the waveguide device is a coplanar waveguide (55). The superconducting filter device (50) according to claim 17, characterized in that the coupling strength between the resonator (51) and the coplanar waveguide (55) is determined by the width of the central conductor (58) and of the gaps (59,59) in the coupler waveguide (55). ). Superconducting filter device according to one of the preceding claims, characterized in that a DC biasing voltage is applied via the connection means (19, 19) (11), for example the central conductor. between the upper plate (14) of the resonator and the coupling means (18), A superconducting bandpass filter or notch filter (10; 20; 30; 40; 50) for use, for example, in a multi-channel communication system comprising a waveguide device (11; 21; 31; 41; 51) operating in high frequency bands, (15; 25 ; 35; 45; 55) and at least one resonator characterized in that the resonator (11; 21; 31; 41; 51) is a parallel plane resonator (12; 22; 32) of which superconducting layer is provided and that the waveguide device (15; 25; 35; 45; 55) comprising a non-linear dielectric material comprises a microstrip conductor, comprising contact means or coupling means (18; 28; 58), where the resonator is so relative to the series resonant circuit is provided thus forming the filter and arranged in the waveguide device that a connecting means (19) are provided through which the frequency of the filter can be tuned. Filter according to Claim 20, characterized in that a DC biasing voltage is applied via the connection means (19). A filter according to claim 20 or 21, characterized in that the microstrip conductor comprising a main microstrip conductor and a central microstrip (18; 28; 58) forming said coupling means. 23. A filter according to any one of claims 20-22, characterized in that the resonator (ll; 2l; 3l; 4l; 5l) consists of a non-linear dielectric bulk material plated with. superconductor (14; 24a, 24b), advantageously high temperature superconductor. A filter (30; 40) according to any one of claims 20-23, characterized in that the resonator (3l; 41) is a dual mode or a multimode resonator. A filter (30; 40) according to any one of claims 20-24, characterized in that it consists of a two-pole comb filter. A filter (10; 20; 30; 40; 50) according to any one of claims 20-25, characterized in that (1l; 2l; 3l; 4l; 5l) that the resonator consists of a chip having an area of approximately between 1 nmf-1 cmÄ to filter enters a A method of signaling as a receiving device in a multi-channel communication system comprising the steps of: - arranging a filter on the input side of the receiving device wherein said filter consists of a parallel plane resonator consisting of a non-linear dielectric material on which superconducting layers are arranged and which arranged on a waveguide device and where means of contact are arranged between said resonator and said waveguide device, for example a microstrip conductor, for effecting a series connection of the resonator and the microstrip conductor, - arranging the resonator and the coupling means so in relation to each other that the coupling strength desired - application of a DC biasing voltage between the contact means for frequency tuning, is not received in it so that interfering signals are extinguished, ie. receiving device. The method of claim 27, comprising the step of providing the filter with the desired coupling strength. through. to give the contact means or coupling means, for example in the form of a central microstrip, such dimensions in relation to the resonator that the desired coupling strength is obtained and that the resonator comprises a non-linear dielectric bulk material plated with HTS films .