WO1997023013A1

WO1997023013A1 - Arrangements and method relating to switching/multiplexing

Info

Publication number: WO1997023013A1
Application number: PCT/SE1996/001689
Authority: WO
Inventors: Erland Wikborg; Spartak Gevorgian
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 1995-12-19
Filing date: 1996-12-18
Publication date: 1997-06-26
Also published as: SE9504531L; SE9504531D0; SE507650C2; JP2000505255A; EP0868763A1

Abstract

The present invention relates to superconducting multiplexing/demultiplexing arrangements (20) comprising a number of signal input means (21, 22) and a number of signal output means (25). A number of resonators (R20) provide(s) a number of filters wherein each filter represents a channel. The resonator(s) (R20) operate(s) at least in dual mode and tuning means are provided so that at least some of the resonators is/are tuneable. The invention also relates to a method of multiplexing signals incoming to a multiplexing arrangement with a number of resonators, each of the resonators having a number of input ports which are so arranged that a number of multipole filters are created. Input signals having different frequencies are supplied to the different input ports of the resonators each of which is operated in three modes. Coupling means are arranged which at least comprise the angle between the input ports and a symmetry plane wherein said angles are non-perpendicularly azimuth. Tuning means are further provided for tuning the resonant frequencies of the degenerate modes and the coupling angles and tuning means are controlled so that for a number of input signals, only one is transmitted to the output means.

Description

Title

ARRANGEMENTS AND METHOD RELATING TO SWITCHING/MULTIPLEXING.

TECHNICAL FIELD

The present invention relates to superconducting switching/multiplexing/demultiplexing arrangements with a number of channels comprising a number of resonators. The invention also relates to filters for microwave signals comprising a number of resonators.

Still further the invention relates to a method for multiplexing/demultiplexing signals.

STATE OF THE ART

For among others multichannel communication systems microwave frequency multiplexers are needed. J. Uher et al., discloses filters in "Tuneable microwave and millimeter-wave passband filters", IEEE Trans. Microwave Theory, 1991, Vol. 39, No. 4, p. 643. If for example the communication systems operate in the frequency band of 1-3 GHz however, the filters get very bulky and their performance characteristics are not satisfactory for a number of reasons, e.g. narrow band, low loss, high power handling capability etc. is needed which cannot be provided to a sufficient extent. In order to design compact filters, resonators nave been constructed which operate in two modes, i.e. dual mode resonators. US-A-5 083 102 discloses a filter with a dual mode dielectric resonator which employs two azimuthally perpendicular degenerate modes. The tuning and coupling between orthogonal modes and dielectric resonators is achieved mechanically by the use of screws. Parallel-plate resonators operating in dual mode are also known. I. Bahl and P. Bharita, "Microstrip Antennas", Artech House, 1980 discusses the use or a notch to provide coupling between two uncoupled orthogonal modes of patch resonators. US-A-5 172 084 shows a filter wherein two degenerate modes of a microstrip patch resonator are used. Two pairs of conducting leads are used to provide two degenerate modes which are azimuthally perpendicular and a special perturber is used to facilitate the coupling between orthogonal modes. However, no tuning is supposed and the filter performance strongly suffer from parasitic surface modes propagating in the common substrate carrying the patches, i.e there are parasitic couplings between the resonators.

In general, all of the filters discussed above are too bulky in particular for communication systems which operate in the 1-3 GHz frequency band and they do not have ideal performance characteristics such as a narrow band, low loss, high power handling capabilities etc. None of the described ways of coupling does provide sufficient flexibility to be used in multichannel multiplexers etc. From US-A-4 881 051 a multiplexer of a branching filter type is known. The design of the multiplexer is very complex and it is based on a plurality of cavities with half- and/or quarter-cut dielectric single mode resonators. The multiplexer has 2-4 channels. In the case of narrow band channels it is extremely critical to manufacturing tolerances. Moreover, since it is limited to a maximum of four channels, presumably it would not work for multichannel systems with a higher number of channels, or in other words either it would not work for more than four channels or it would be even more complex and in no way cost-effective. Still further, the multiplexer does not seem to be tuneable which means that it can not be used in systems wherein tunability is required. SUMMARY OF THE INVENTION

What is needed is therefore a filter or particularly a multiplexing arrangement, which is small and compact. Moreover, what is needed is a filter which can be used in multiplexing (demultiplexing) arrangements or particularly a multi-pole channel filter with a straightforward and non-complex design and which can be used in communication systems which operate for example in approximately the 1-3 GHz frequency band without being bulky and which have good performance characteristics, i.e. narrow band, low loss, high power handling capability etc. Moreover a resonator is needed which operates in multiple mode and which is suitable for filters and multiplexing arrangements for use for example in multichannel communication systems. Moreover a method for multiplexing signals in a multichannel communication system is needed which is efficient, has a high power handling capability and only gives rise to low losses.

What is needed is therefore also a superconducting multiplexing arrangement which comprises a number of signal input means and a number of signal output means and which further comprises a number of resonators which provide a number of filters which in turn each represent a channel wherein the resonators at least operate in two modes and wherein at least some of the resonators are tuneable. Particularly, a current and/or an electric field redistribution needs to be produced, e.g. through introducing an asymmetry in the resonator, in order to create degenerate resonator modes.

Therefore, in order to provide for mutual coupling between degenerate modes in the resonators coupling means are provided which according to a particular embodiment form an angle for which the degenerate modes become coupled and which is achieved by arranging of input/output means either in relation to each other or in relation to a symmetry axis of the resonator in an appropriate way. The coupling angle is advantageously the azimuthal angle between the signal input and the resonator symmetry axis and the degenerate modes are non-orthogonal. According to a particular embodiment second coupling means can be provided which are used for controlling the strength of the coupling between the degenerate modes and/or for controlling the resonant frequencies of the coupled degenerate modes. The second coupling means may for example comprise notches arranged on the resonators and they are particularly used to provide for controlling for a given coupling angle. Advantageously the lowest orders of degenerate modes are coupled, particularly TM (transverse magnetic) modes. The resonant frequencies of at least some resonators can be tuned and the tuning is advantageously provided through applying and controlling a voltage through biasing means. Alternatively a number of the resonators may be optically tuneable and/or they can be temperature controlled/tuned. According to an advantageous embodiment the resonators are triple mode resonators which means that they operate in three different degenerate modes. The multiplexing arrangement advantageously comprises a number of filters which are formed by a number of resonators and advantageously the number of resonators does not exceed the number of filters which means that the number of resonators for a number of multi-pole channel filters is considerably reduced as compared to hitherto known frequency combining arrangements.

A particular embodiment relates to a two-channel multiplexer which comprises a resonator with two input ports and an output port forming two channels each of which comprises a two-pole filter. Coupling is provided by the first and second azimuthal coupling angles between the resonator symmetry axis and the first and the second signal input port respectively. A first tuning or biasing for example consist in that no biasing is applied (or anything else), so that only one of the first and second input signals is output via the signal output means of the signal output port whereas for a different biasing or tuning condition only the other of the input signals is output via the signal output means. The biasing or tuning may be provided by the application of a biasing voltage. Alternatively or additionally temperature or optical tuning can be used.

According to another embodiment the arrangement comprises a four-channel multiplexer with four inputs and a common output and which comprises three tuneable resonators. It is a branching filter multiplexer wherein each branch comprises a four-pole filter. The first and second coupling means and the biasing conditions are so chosen that only one of four input signals is output via the common output means. According to still another embodiment the arrangement comprises an eight-channel multiplexer which is formed by seven resonators with six-pole tuneable filters in each branching channel. Still further it may be a multi-channel multiplexer having more than eight channels.

According to an advantageous embodiment the resonators (relevant to all embodiments) are parallel-plate resonators. The resonators may e.g. be disk, ring, rectangular resonators or they may even have any arbitrary shape. Still further, the resonators may be made from a non-linear bulk material having a high dielectric constant and which is at least partly covered by high temperature superconducting HTS films. This is extremely advantageous for the forming of even smaller and compacter resonators. Particularly a resonator is provided which operates in three modes for which the coupling is given by the azimuthal angle between the degenerate modes and wherein the degenerate modes are not azimuthally perpendicular. The angle between them and the coupling between them is produced by the arranging of input/output ports in a corresponding way and the resonator is additionally controlled or tuned for example electrically. Alternatively it may be optically or temperature controlled. Mechanical turning can also be applied, e.g. using piezoelectric means. As an alternative additional coupling means may be provided for example in the form of (a) notch(es) or similar.

A multi-pole filter is also provided which comprises a number of multimode resonators with three azimuthally degenerate modes.

It is an advantage of the invention that a particularly small compact arrangement is provided and which can be used for communication systems, for example telecommunications systems operating in the 1-3 GHz frequency band. A particular advantage of the invention is that, particularly if the triple mode regime is used, the reduction of the numbers of resonators per channel or per filter can be considerably reduced. The multiplexer size is thereby also further reduced. It is also an advantage that additional functional flexibility for microwave systems wherein tuneable frequency channels are needed, for example adaptive and/or reconfigurable microwave system etc. is provided. Another advantage of the invention is that the manufacturing tolerances are not critical for the filter or multiplexer which as such make the arrangement more robust and less sensitive to faults etc.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be further described in a non-limiting way under reference to the accompanying drawings in which:

FIG 1A illustrates a parallel-plate circular disk resonator with symmetric excitations, FIG 1B illustrates a parallel-plate circular disk resonator with asymmetric excitations, FIG 2A-D illustrates the field and current distribution of the first four lowest order modes in a parallel-plate circular disk resonator, FIG 3A illustrates the current distribution of a single lowest order mode in a circular parallel-plate resonator, FIG 3B illustrates the current distributions of two degenerate lowest order modes in a resonator as above, FIG 4 illustrates the temperature dependence of the resonant frequencies of the four lowest order modes of a superconducting parallel-plate resonator, FIG 5 illustrates the voltage dependence of the resonant

frequencies, FIG 6 shows a tuneable two-pole filter, FIG 6A illustrates the passband of the filter of fig. 6 for a first biasing condition, FIG 6B illustrates in- and output signal frequency for the biasing condition of Fig 6A, FIG 6C shows the passband of the filter for a second biasing condition, FIG 6D is a Fig similar to Fig 6B for the biasing condition of

Fig 6C, FIG 7 illustrates a tuneable two-channel multiplexer,

FIG 7A illustrates the passband for the multiplexer of Fig 7 for a first biasing condition,

FIG 7B illustrates the input signals and the output signal fro the biasing condition of Fig 7A. FIG 7C illustrates the passband for the arrangement cf Fig. 7 for a second biasing condition,

FIG 7D shows the input and output signals for the second

biasing condition of Fig 7C,

FIG 8 shows a four-channel multiplexer, and FIG 9 shows an eight-channel multiplexer.

DETAILED DESCRIPTION OF THE INVENTION

Fig 1A illustrates, for explanatory reasons, a parallel-plate circular disk resonator with symmetric excitations. The circular parallel-plate disk resonator 1A comprises a single-crystal non-linear dielectricum 2 which is partly covered for example by high temperature superconducting (YBCO) or Au plates 3,3 which may be deposited by some known method (this is among others discussed in Z-Y Shen, "High Temperature Superconducting Microwave Circuits", Artech House 1994). This will be further discussed below. The superconductors are arranged on both the flat surfaces of the dielectric material 2. Connections 6 are used for voltage biasing and the input and output couplings 4,5A are symmetrically arranged in relation to a symmetry plane or a symmetry axis 6, 6A of the resonator. In Fig 1B, however, the input and output coupling ports are so arranged that an asymmetry is introduced in the otherwise perfectly symmetric resonator. The resonator of fig 1B, which in all other aspects corresponds to the resonator of Fig 1A is provided with an asymmetry in that the output port and the input port are so arranged that they are azimuth in relation to a symmetry plane 6B.

The distributions of currents and of the magnetic and electrical fields for the four lower order TM modes of a circular (perfectly axially symmetric) disk resonator for which the thickness of the dielectricum is less than the microwave signal wavelength in the dielectricum, are shown in Fig 2A-D. The resonant frequencies of perfectly symmetric resonators are given by

as discussed in "Microstrip Antennas", Artech House 1980 by I. Bahl, P. Bharita. c₀ is the velocity of light in vacuum, a is the radius of the disk, ε is the dielectric constant and K_mn is the m-th zero of the derivative of the Bessel function of order n. In Figs 2A-D a continuous line with an arrow indicates the current in the top plate whereas a dashed-dotted line indicate the magnetic field and •, x indicate the electric field in a generally recognised manner. For the lowest order TMn mode, K_mn=1.8412. The current distribution for this mode is shown in Fig 3A wherein continous lines indicate the current and .,x indicate the direction of the electrical field. If an asymmetry is introduced in the disk, this produces a field/current redistribution, the result of which being that degenerate modes are created. As already referred to above an asymmetry may be introduced by arranging the input and output coupling ports in the proper places, for example as schematically indicated in Fig 1B. Of course an asymmetry may also be introduced in other ways. In Fig 3B a current distribution is shown ror = resonator in which the input and output excitation points are shifted by an angle Φ. In the figure a continuous line indicates current lines for the basic (excited) TM₁₁ mode whereas a dashed line indicates current lines for the degenerate (output) TM₁₁ mode.

However, the mutual coupling between two degenerate modes vanishes for an angle of approximately 90°. For this angle the degenerate modes or the perfectly symmetric resonator are not coupled and the resonant frequencies of the two modes are in practice the same. However, for other angles and/or any asymmetry in the resonator, coupling is produced between the degenerate modes. In "Fundamentals for Microwave Engineering" by R.E. Collin, McGraw-Hill, 1966 the coupled wave theory is discussed and the coupled degenerate modes result in two new modes having slightly different frequencies. If the angle is correctly chosen, the degenerate modes can be mutually coupled and the resonator is forced to operate as a two-pole filter with either maximally flat or with Chebyshev passbands. For a fixed angle the coupling strength between the modes, therethrough also the resonant frequencies, can be controlled through the introduction of additional coupling means. These additional coupling means, in the following denoted second coupling means, may for example comprise a notch in a plate of a parallel plate resonator or anything similar. Of course a number of other alternatives are also possible.

In Figs 6-9 a number of different embodiments of the present invention will be shown. However, before going into detail as far as these particular embodiments are concerned, examples will be given on how the resonators can be made. The following discussion is also relevant to the particular embodiments as discussed under reference to Figs 6-9 as well as to further embodiments which are not discussed here but which also fall within the scope of the invention. The invention is however not limited to resonators made as described below, but the following examples only relate to embodiments through which it is possible to still more reduce the size or the resonators and thus also of the filters and multiplexers and to even further improve the tunability.

High temperature superconductors, in the following denoted HTS, have extremely low microwave losses at temperatures of liquid nitrogen, in the following denoted N_liq, at 77 K. In an advantageous embodiment HTS is used for narrow-band filters with low losses for multichannel communication systems. HTS microwave circuits are discussed in Z-Y Shen in "High temperature Superconducting Microwave Circuits", Artech House 1994. Small size electrically and/or temperature controlled resonators having very high Q-values in the 1-3 GHz frequency band can be realized through the integration of HTS with non-linear dielectric materials. This is among others discussed in "1 GHz tunable resonator on bulk single crystal SrTiO₃ plated with YBCO", by O.G. Vendik et al., in Electron. Letters, 1995, Vol. 31, No 8, p. 654. Therein a resonator is discussed which however is mounted in a coaxial fixture. Among others because of that it is not suited for dual mode operation and use in multichannel multiplexers. Moreover, the dimensions are not as small as needed for such applications which among others is due to the fact that not the lowest resonant mode is used which according to the present invention is advantageous and contributes in reducing the dimensions. However, non-linear dielectric single crystalline materials such as for example strontium titanate STO have extremely high dielectric constants and moreover the microwave losses are very low in the temperature range below the boiling temperature of N_liq. Thus, as referred to above, a non-linear dielectricum such as e.g. STO car be used to still further reduce the size of the resonators but also to tune the resonant frequency of the resonator. Tuning may either be effected through the control of an applied voltage or controlling of the temperature. Alternatively optical tuning can be applied. In Fig 6 is illustrated how the resonant frequencies of the four lowest order modes of a superconducting parallel plate resonator depend on temperature. It follows from the almost linear dependence of the resonant frequencies of all modes below 80K that the reduction of the dielectric constant of STO has a T^-2 dependence in this temperature range.

The four lowest TM modes, TM₀₁, TM₁₁, TM₂₁ and TM₃₁ have K values K₀₁=3.8317, K₁₁=1.8412, K₂₁=3.0542 and K₃₁=4,2012 and within these four lowest modes, the lowest frequency belongs to the TM₁₁ mode. For example for a resonator having a diameter 5 mm, the resonant frequency of this mode is close to 0.95 GHz at 77K when no biasing voltage is applied. In Fig 5 is illustrated how the resonant frequency of the TM₁₁ mode depends on the applied voltage for two different temperatures, 35K and 75K. "a" illustrates the dependence of the TM₁₁ mode on the applied voltage at 35K whereas "b" illustrates the corresponding dependence at 75K.

The small differences in resonant frequencies of the degenerate modes referred to above and the temperature and the voltage dependencies of these frequencies can be used to control passband filters and multiplexers by varying the bias voltage or the temperature etc. One example of a double mode performance STO parallel plate disc resonator with superconducting plates for example of YBCO can according to one particular example, which merely is given for illustrative purposes, have a resonator diameter of about 10 mm and a dielectric thickness of about 0.5 mm. The coupling angle may be about 10° and the first and second biasing voltages can for example be 0 V and 200V respectively. This is however merely to be interpreted as one example among many others.

Fig 6 illustrates a tuneable multiplexer-filter/switch 10. A microwave signal with the frequency f₀ is supplied to the input port 11 of a two-pole filter comprising a dual mode tunable resonator P 10. Signal output means in the form of a signal output port 12 are provided through which a signal is output. The angle

Φ₁₀ comprises the first coupling means whereas a notch or a similar constitute the second coupling means 13. Fig 6A and Fig 6B illustrate the passband of the filter 10 for first biasing conditions e.g. corresponding to a voltage V₀ and/or a temperature T₀. For these first biasing condition, e.g. corresponding to zero voltage, the central frequency of the filter coincides with the frequency of the input signal. The input signal having the frequency f₀ is then transmitted through the filter with the lowest possible attenuation. The resonator is shown in Fig 6B, i.e. it can be seen from the figure that the input signal with frequency f₀ is also output from the filter.

Fig 6C shows the passband of the filter for a second biasing condition corresponding for example to an applied voltage V and/or a temperature T₁. The passband is then shifted so that the signal frequency of the input signal falls in the rejection band and it is strongly attenuated at the output port 12. As can be seen from Fig 6D, in this case no signal is output. The performance of the filter, which here is a passband filter, is given, or can be controlled by the angle Φ₁₀ that the signal input port 11 for the input signal forms with a symmetry plane of the resonator wherein the angle forms the first coupling means. Advantageously it can be additionally controlled by second coupling means 13. The tuneable filter/switch as illustrated in Figs b-6D can be said to form a basic unit of more complexe tuneable filters or multiplexing arrangements as will be discussed below.

In Fig 7 a second embodiment is illustrated which comprises a tuneable two-channel multiplexer 20. A first and a second microwave signal f₁, f₂ are supplied to a first input port 21 and to a second input port 22 respectively of a single parallel-plate circular disk resonator R 20. The frequencies f₁, f₂ differ slightly. The output port 25 forms a two-pole filter with the first input port 21 in a manner similar to that as described under reference to Fig 6. This filter will in the following be denoted filter B. The performance of filter B is determined by the first coupling means, i.e. the angle Φ₂₁ and the second coupling means 23, 24. A second two-pole filter is in a similar manner formed between the second input port 22 and the output port 25 which is a common output port both for the first and for the second input ports. This filter will in the following be denoted filter C. Its performance is correspondingly given by angle Φ₂₂ and the second coupling means 23, 24. In Fig 7A the passbands for filters B and C respectively are illustrated for a first biasing condition for example corresponding to a voltage and/or temperature biasing condition V0, T0. The first coupling means, i.e. the coupling angles Φ₂₁, Φ₂₂ and the second coupling means 23, 24 are so chosen that the frequency of the first input signal f₁ is in the passband of filter B whereas the frequency of the second input signal f₂ is in the rejection band of filter C. Consequently only the input signal with the first input frequency f₁ is output from the common signal output means 25. This can also be seen from Fig 7B. In a similar manner Figs 7C and 7D illustrate the passbands for a second biasing condition corresponding to voltage and/or temperature biasing conditions V1, T1 wherein only the second input signal f₂ appears at the output port 25. The coupling is primarily given by the azimuthal angle between degenerate modes which is given by the arranging of the input/output ports. In the embodiment illustrated here, there is a two-pole filter in each channel.

Fig 8 illustrates another embodiment of the invention which relates to a four-channel multiplexer 30. According to the present invention, only three resonators R1, R2, R3 are required for a four-channel branching filter multiplexer. In the present embodiment all of the three resonators are tuneable. The multiplexer 30 comprises four input means in the form of four input ports 31, 32, 33, 34 of which two 31, 32 are comprised by a first resonator R1 and input ports 33, 34 are comprised by the second resonator R2. One common output port 35 is comprised by the third resonator R3. There is thus one common output port for all the input ports. The first resonator R1 forms a two-channel multiplexer with the third resonator R3 wherein said multiplexer comprises two four-pole tuneable branching filters. The second and the third resonators R2, R3 in a similar manner form another two-channel four-pole filter. The first and the second coupling means, i.e. here the coupling angles Φ₃₁, Φ₃₂, Φ₃₃, Φ₃₄ and the second coupling means 36, 37, 38, 39 and the respective coupling strength between the resonators as well as the biasing conditions are so chosen that only one of the input signals with either of the frequencies f ₁ , f₂, f₃, f₄ can be transmitted to the output port 35. It can thus be seen that only three resonators are needed to provide a four-pole branching filter multiplexer, which is advantageous. In Fig 9 an eight-channel multiplexer 40 is illustrated. The multiplexer 40 comprises eight input ports for signals with the frequencies f₇'' to f₈'' and there is one common output to which one of the input signals can be transmitted. As already discussed above this is given by the first and second coupling means, i.e. the coupling angles between respective axis of the resonators and signal input ports so that three degenerate azimuthal non-perpendicular modes are created. This is not further discussed here since the same principles apply as discussed in relation to the other embodiments. However, it can be seen that for an eight-channel multiplexer only seven resonators R40 are needed. The resonators forms six-pole tuneable filters in each branching channel. As a comparison, to make an eight-channel multiplexer as a traditional combiner with one-pole dielectric resonators, 48 resonators would have been required.

According to the present invention also higher order multiplexers can be provided using the same principles, which however not need to be illustrated in any figure since it should be clear from the foreging how such should be made.

Even if the invention has been more carefully described under reference to multiplexing arrangements, it is obvious that it also applies to demultiplexing arrangements. The invention applies to resonators having substantially any form such as disk, ring, rectangular or any arbitrary shape or particularly any kind of parallel-plate resonators but it is also possible to use so called image resonators. Earlier in the description resonators comprising bulk crystal like dielectric materials such as STO plated with e.g.

YBCO or any another HTS-material. This relates to advantageous embodiments through which for example the size can be even more reduced. It should be clear that this merely relate to particular embodiments. The resonators can also be made in other ways and the superconducting material does not have to be high temperature superconducting material etc. The invention is also in the other aspects not limited to the shown embodiments but it can be varied in a number of ways and particularly it relates to demultiplexers as well as to multiplexers.

Claims

1. Superconducting switching or (de)multiplexing arrangement (10; 20; 30; 40) comprising a number of signal input means (11; 21; 22; 31; 32; 33; 34), a number of signal output means (12;25;35) and a number of resonators (R10;R20;R1, R2, R3; R40) providing a number of filters, each filter representing a channel, the resonator(s) (R10;R20;R1, R2, R3; R40) at least operating in dual mode,

c h a r a c t e r i z e d i n

that asymmetries are produced in the resonator (s) to provide a current/electric field redistribution so that degenerate resonator modes are created, and in that tuning means are provided so that at least some of the resonators are tunable.

2. Arrangement according to claim 1,

c h a r a c t e r i z e d i n

that first coupling means (Φ₁₀; Φ₂₁; Φ₂₂;Φ₃₁, .. , Φ₃₄) are provided to provide mutual coupling between degenerate modes in a resonator (R10; R20; R1, R2, R3; R40).

3. Arrangement according to claim 1 or 2,

c h a r a c t e r i z e d i n

that the input/output means are so arranged in relation to each other or in relation to a symmetry axis of the resonator that at least one angle is formed for which the degenerate modes become coupled, said angle forming first coupling means

(Φ₁₀; Φ₂₁; Φ₂₂; Φ₃₁, ... , Φ₃₄) .

4. Arrangement according to claim 3,

c h a r a c t e r i z e d i n that the coupling angle is the azimuthal angle between the signal input and the resonator symmetry axis and in that degenerate modes are non-orthogonal.

5. Arrangement according to anyone claims 2-4,

c h a r a c t e r i z e d i n

that second coupling means (13; 23, 24; 36, 37, 38, 39) are provided for controlling the strength of the coupling between the degenerate modes and/or for controlling the resonant frequencies of the coupled degenerate modes for a given coupling angle.

6. Arrangement according to claim 5,

c h a r a c t e r i z e d i n

that the second coupling means (13; 23, 24; 36, 37, 38, 39) comprise a number of notches arranged on the resonators.

7. Arrangement according to anyone of the preceding claims,

c h a r a c t e r i z e d i n ,

that the lowest orders of degenerate (TM) modes are coupled.

8. Arrangement according to anyone of the preceding claims,

c h a r a c t e r i z e d i n

that at least some of the resonators are electrically tunable, i.e. the resonant frequencies can' be tuned, wherein the tuning is provided e.g. by the application of a voltage through biasing means.

9. Arrangement according to anyone of the preceding claims,

c h a r a c t e r i z e d i n

that at least a number of the resonators are optically or mechanically tunable and/or in that temperature tuning is applied.

10. Arrangement according to anyone of the preceding claims, c h a r a c t e r i z e d i n

that at least a number of the resonators (R10;R20; R1, R2, R3;R40) are triple mode resonators, i.e. operate in three modes.

11. Arrangement according to claim 10,

c h a r a c t e r i z e d i n

that the resonators comprise three azimuthal degenerate modes.

12. Arrangement according to anyone of the preceding claims, c h a r a c t e r i z e d i n

that a number of filters are provided and in that the number of resonators needed to provide a given number of filters does not exceed the number of filters.

13. Arrangement according to anyone of the preceding claims, c h a r a c t e r i z e d i n

that the arrangement (10) comprises a switch which comprises one resonator (R10) wherein the input port forms an azimuth coupling angle (Φ₁₀) with the symmetry axis for which coupling is provided between degenerate modes so that depending on biasing condition an input signal is transmitted to the output port or prevented form being transmitted to the output port.

14. Arrangement according to anyone of claims 1-12,

c h a r a c t e r i z e d i n

that it is a two-channel multiplexer (20) comprising a resonator (R20) wherein each channel comprises a two-pole filter and in that coupling is given by the first and second azimuthal coupling angles (∅₂₁, ∅₂₂) between the resonator symmetry axis and first and second signal input means (21,22) respectively, said first and second signal input means (21,22) having a common signal output means (25).

15. Arrangement according to claim 14,

c h a r a c t e r i z e d i n

that for a first tuning or biasing condition (V₀, T₀) only the first input signal (f₁) is output via the signal output means (25) whereas for a second biasing condition (V₁, T₁) only the second input signal (f₂) is transmitted to the signal output means (25).

16. Arrangement according to anyone of claims 1-12,

c h a r a c t e r i z e d i n

that it is a four-channel multiplexer (30) with four input ports (31, 32, 33, 34), a common output port (35), and in that it comprises three tunable resonators (R1, R2, R3).

17. Arrangement according to claim 16,

c h a r a c t e r i z e d i n

that it is a branching filter multiplexer, wherein each branch comprises a four-pole filter.

18. Arrangement according to claim 16 or 17,

c h a r a c t e r i z e d i n

that a first (R1) and a second (R2) of said resonators comprise two four-pole tunable branching filters and in that a third resonator (R2) forms two further four-pole tunable filters with the first resonator (R1).

19. Arrangement according to anyone of claims 16-18,

c h a r a c t e r i z e d i n

that the first (Φ₁₀; Φ₂₁, Φ₂₂; Φ₃₁, Φ₃₂, Φ₃₃, Φ₃₄) and second (13; 23, 24; 36, 37, 38, 39) coupling means and the biasing conditions are such that only one of four input signals is output at a time.

20. Arrangement according to anyone of the claims 1-12, c h a r a c t e r i z e d i n

that it is an eight-channel multiplexer (40) comprising seven resonators (R40) with six-pole tunable filters in each branching channel.

21. Arrangement according to anyone of the preceding claims, c h a r a c t e r i z e d i n

that it is a multichannel multiplexer having more than eight channels.

22. Arrangement according to anyone of the preceding claims, c h a r a c t e r i z e d i n

that the resonators are made from a non-linear bulk material with a high dielectric constant at least partly covered by high temperature superconducting (HTS) films.

23. Arrangement according to anyone of the preceding claims, c h a r a c t e r i z e d i n

that the resonators (1B; R10; R20; R1, R2, R3; R40) are parallel plate resonators.

24. Arrangement according to anyone claims 1-23,

c h a r a c t e r i z e d i n

that the resonators are disk, ring, rectangular resonators or resonators of an arbitrary shape.

25. Arrangement according to anyone the preceding claims,

c h a r a c t e r i z e d i n

that the filters are bandpass filters.

26. Tuneable filter for electromagnetic signals with a number of input ports and a number of output ports and comprising a number of resonators,

c h a r a c t e r i z e d i n

that asymmetries are produced in the resonator(s) to provide a current and/or an electric field redistribution so that degenerate resonator modes are created, each resonator being a multimode resonator, and in that tuning means are provided for tuning the resonant frequencies of the degenerate modes.

27. Tuneable filter according to claim 26,

c h a r a c t e r i z e d i n

that each resonator comprises at least two azimuthllyy degenerate modes which are not perpendicular and in that the coupling between the degenerate modes is given by the azimuthal angle between the respective input port and the resonator symmetry plane.

28. Tuneable filter according to claim 27,

c h a r a c t e r i z e d i n

that three azimuthal degenerate modes are used, i.e. the resonator is a triple mode resonator.

29. Tuneable filter according to claim 27 or 28,

c h a r a c t e r i z e d i n

that the tuning means comprise electrical connection for the application of a biasing voltage.

30. Method for multiplexing electro-magnetic signals incoming to a multiplexing arrangement comprising a number of resonators with each a number of input ports so arranged that a number of multipole filters are created,

c h a r a c t e r i z e d i n

that it comprises the steps of: - supplying a number of input signals having different frequencies to the different input ports of resonators each of which

comprises at least two input ports,

- operating each resonator in three modes,

- arranging coupling means for the resonator wherein said coupling means comprises the introduction of asymmetries to provide a current and or an electric field redistribution so that

degenerate nodes are formed,

- providing tuning means for tuning the resonant frequencies of the degenerate modes,

- controlling the coupling angles and tuning means in such a way that for a number of input signals, only one can be transmitted to the output means.

31. Method according to claim 30,

c h a r a c t e r i z e d i n

that the coupling means comprises at least the angles between the input ports and a symmetry axis, which angles are non-perpendicularly azimuth.

32. Method according to claim 30 or 31,

c h a r a c t e r i z e d i n

that the tuning is electrical.