WO2022096181A1

WO2022096181A1 - Tunable resonator apparatus and method

Info

Publication number: WO2022096181A1
Application number: PCT/EP2021/074886
Authority: WO
Inventors: Senad Bulja; Dirk Wiegner; Wolfgang Templ; Ari Juhani Vilander
Original assignee: Nokia Technologies Oy
Priority date: 2020-11-06
Filing date: 2021-09-10
Publication date: 2022-05-12

Abstract

An apparatus such as a tunable filter is disclosed. The apparatus has multiple resonator members arranged in an array between two conductive plates. There is at least one electrically active component associated with at least a subset of the resonator members, the electrically active components being arranged between the two conductive plates and adjacent to or forming a part of the associated resonator member. There is a controller for controlling an electrical characteristic of the electrically active components and thereby changing a frequency response of the resonator member. The controller is configured to change a frequency response of the apparatus by controlling the frequency response of the at least a subset of the resonator members.

Description

TUNABLE RESONATOR APPARATUS AND METHOD

TECHNOLOGICAL FIELD

Various example embodiments relate to tunable resonator apparatus such as tunable filters, and methods of tuning resonator apparatus.

BACKGROUND

Filters are widely used in data transmission and in particular, telecommunications, for example in base stations, radar systems, amplifier linearization systems, point-to-point radio, and RF signal cancellation systems. They are important components of mobile radio transceivers in order to e.g. a) inhibit the transmission of interfering or disturbing signals in unwanted frequency bands and b) inhibit receivers from being disturbed by their own or other external disturbing signals (blockers, etc.). Despite their essential contribution in transceiver designs, filters are usually not frequency tunable without significant effort, leading to frequency and application specific designs which may require fairly onerous manual tuning.

For this reason a large variety of filters has to be made available to adequately address the large number of frequency bands, applications, markets, etc. Due to this situation, filters are also a serious bottleneck for flexible and thus more sustainable systems like multiband & software defined radio applications.

In addition to mobile radio application, there are other applications requiring resonators in general and filters in particular, such as fixed communication and oscillators, these would also benefit from frequency tunable resonators and/or filters.

BRIEF SUMMARY

The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

According to various, but not necessarily all, embodiments of the invention there is provided a distributed resonator-based apparatus comprising: multiple resonator members arranged in an array between two conductive plates; at least one electrically active component associated with at least a subset of said resonator members, said at least one electrically active component being arranged between said two conductive plates and adjacent to or forming a part of said associated resonator member; and a controller for controlling an electrical characteristic of said at least one electrically active component and thereby changing a frequency response of said associated resonator member; said controller being configured to change a frequency response of said apparatus by controlling said frequency response of said at least a subset of said resonator members.

Apparatus comprising resonator members may act as filters or oscillators and their frequency of operation is generally dependent on their configuration. Providing electrically active components associated with at least a subset of the resonator members in a resonator apparatus allows the electrical characteristics of the electrically active components to be controlled. This has a corresponding effect on the frequency response of the resonator member associated with the electrically active component. Controlling the frequency response of individual resonator members allows the frequency response of the whole apparatus to be correspondingly controlled. Electrically active components allow for electrical as opposed to mechanical control, which control is generally simpler and more robust.

Providing a resonator apparatus where the frequency response is electrically controllable allows the apparatus to be tunable. Thus, where the apparatus is used in a filter for example, a tunable bandwidth, high pass or low pass filter can be provided and where the apparatus is an oscillator for example, the frequency response of the oscillator may be controlled.

The controller may be a control means for controlling an electrical characteristic of the at least one electrically active component, it may be control circuitry configured to control an electrical characteristic of the at least one electrically active component, and it may comprise a processor configured to provide the control function.

In some embodiments there is at least one electrically active component associated with each of the at least a subset of the resonator members.

In some embodiments, the array of resonator members may comprise the resonator members arranged in a regular or an irregular geometric pattern between the conductive plates. In some embodiments, the resonator members may be arranged such that one end is connected, or close to, one of the conductive plates while the other end of the resonator member extends towards the other of the conductive plates.

In some embodiments, the controller is configured to change the biasing voltage applied to the electrically active component and thereby change the electrical characteristic of the electrically active component.

In some embodiments the electrical coupling between the resonator members and/or the resonator member and the conductive plates may be changed by changing the electrical characteristics of the electrically active component and in this way the frequency response of the resonator member is controlled. Providing electrical, nonmechanical control allows for a robust, effective and compact apparatus.

In some embodiments said at least one electrically active component is arranged between said resonator member and one of said conductive plates.

In some embodiments said resonator member has an outer surface formed of a conductive material, in some embodiments a metallic material.

In some embodiments said resonator member comprises a 3D object having a longitudinal axis at an angle of between 6o° and 120⁰ to said conductive plates, preferably substantially at 90° to said conductive plates.

In some embodiments, said conductive plates are substantially parallel to each other.

In some embodiments, said electrically active components comprise at least one of: a switching mechanism configured to connect or disconnect said resonator member from one of said conductive plates; and an electro-active material adjacent to said resonator member, changing in a biasing voltage across said electro-active material changing the dielectric permittivity of said electro-active material.

In some embodiments, at least a first subset of said multiple resonator members comprise a switching mechanism arranged between said resonator member and one of said conductive plates, said switching mechanism being configured to electrically connect or disconnect said resonator member from said one of said conductive plates in response to a control signal from said controller.

In some embodiments the other end of the resonator member remote from the switching mechanism is at a distance from the other of said conductive plate. In some embodiments, connecting the resonator via the switching mechanism to the conductive plate activates the resonator, while isolating the resonator from the conductive plate deactivates the resonator.

In some embodiments, at least a second subset of said multiple resonator members each comprise said electrically active component as an end portion adjacent to one of said conductive plates and comprising an electro-active material, said controller being configured to control a biasing voltage applied to said electro-active material to change a dielectric permittivity of said electro-active material.

In some embodiments, the first and second subset are the same subset, in some embodiments, the first and second subset are different subsets, in some embodiments, the first and second subsets are overlapping subsets, with some shared resonator members, and some resonator members unique to that subset.

In some embodiments, said at least a first and at least a second subset comprise a same at least a subset of said multiple resonator members, such that each resonator member in said at least a subset comprises one of said switching mechanisms to connect one end of said resonator member to one of said conductive plates and one end of said resonator member comprises an electro-active material.

Having a switching mechanism and an electro-active material on a same resonator member, allows coarse tuning of the frequency response by activating or deactivating the respective resonator members and fine tuning of the frequency response by changing the dielectric permittivity of the electro-active material when the associated resonator member is activated.

In some embodiments, the switching mechanism and electro-active material are at a same end of the resonator member, while in other embodiments they are at opposite ends of the resonator member. In some embodiments, said electro-active material comprises at least one of a liquid crystal material and an electro-chromic material

In some embodiments, said controller is configured to form groups of said resonator members to control a frequency response of said resonator members within a same group in a same way.

Controlling the resonator members in groups allows for less complexity in the control, although there may be lower granularity in the controlled frequency response.

In some embodiments the control is performed in accordance with the geometric locations of the resonator members.

In some embodiments, said resonator members comprise vias within a laminate structure, said laminate structure being held between said conductive plates.

In some embodiments, said vias are tubular holes with surfaces comprising electrically conductive material at least when the resonator member is activated.

In some embodiments the tubular holes are cylindrical, and in others they may have a semi-circular or quarter circular cross section.

In some embodiments, said resonator members comprise posts arranged in a cavity formed by a conductive housing, said conductive housing comprising said conductive plates.

In some embodiments, said resonator members are mounted to form a plurality of substantially cylindrical posts, at least some of said plurality of substantially cylindrical posts comprising a plurality of resonator members each of said plurality resonator members forming a portion of said substantially cylindrical post, said plurality of resonator members forming a cylindrical post being mounted adjacent but separate to each other.

In some embodiments, at least a subset of said cylindrical posts each comprises at least one electrically active component arranged between said resonator members forming said cylindrical post. In some embodiments, said at least one electrically active component comprises an electro-active material and/ or a switch.

In some embodiments, said apparatus further comprises: a data store configured to store frequency responses and corresponding control signals applied to said electro-active components for said apparatus; wherein said controller is configured to: receive a signal indicating a target frequency response; determine from said data store the corresponding control signals to apply to said electro-active components to provide a frequency response at or close to said target frequency response.

In some embodiments, the target frequency response, comprises at least one of a target frequency, a target frequency bandwidth and a target frequency selectivity characteristic.

In some embodiments, said apparatus further comprises: circuitry for detecting a frequency response of said apparatus; wherein said controller is configured to determine said frequency response of said apparatus on applying said control signals retrieved from said data store; and to amend at least one of said control signals and determining an updated frequency response; and to continue amending said at least one control signal and determining said updated frequency responses until a frequency response sufficiently close to said target frequency response is obtained; and to maintain said updated control signals and update said data store.

In some embodiments, said controller is configured on receiving a target frequency response to: select a subset of said plurality of resonator members to activate or deactivate by controlling said switching mechanism associated with said subset to electrically connect or disconnect said subset of said plurality of resonators from said one of said conductive plates in order to set a frequency response of said apparatus close to said target frequency response, and where said frequency response is not within a threshold amount of said target frequency response; and to control a biasing voltage applied to said electro-active material of said subset of activated resonator members to change a dielectric permittivity of said electro-active material to fine tune a frequency response of said apparatus.

Where resonator members have both a switching mechanism and an electro-active material associated with them then the controller may first coarse tune the frequency response by controlling the switching mechanism and then if required fine tune the response by controlling the electro-active material. Where the resonator members have only one electrically active component then the controller controls the frequency response by controlling at least a subset of the electrically active components.

In some embodiments, said apparatus comprises multiple resonator members arranged in at least two arrays between said two conductive plates, said at least two arrays forming separate linked resonator apparatus, said apparatus comprising a signal path for a signal to pass between said at least two arrays; wherein at least one of said electrically active component is associated with each of at least a subset of said resonator members in each of said at least two arrays; and said controller is configured to change a frequency response of said apparatus by separately controlling said frequency response of said at least a subset of said resonator members in each of said at least two arrays, such that a frequency response of said two resonator apparatus are controlled independently of each other.

The resonator apparatus may be arranged to form two or more arrays of resonator members each individually controlled so that a frequency response of each array of resonator members can be separately controlled allowing a band pass filter for example to be provided.

In some embodiments the two or more arrays are arranged in two or more separate cavities, the signal path between the arrays comprising an iris in the wall linking adjacent cavities.

According to various, but not necessarily all, embodiments of the invention there is provided a method of tuning a frequency response of an apparatus according to a first aspect comprising: for a plurality of resonator members, changing a control signal applied to at least one electrically active component associated with said plurality of resonator members and thereby changing an electrical response of said plurality of resonator members. In some embodiments, at least one of said electrically active components comprises a switching mechanism and said step of changing a control signal applied to said electrically active component comprises controlling said switching mechanism to connect or disconnect said resonator member from one of said conductive plates.

In some embodiments, connecting the resonator via the switching mechanism to the conductive plate activates the resonator, while isolating the resonator from the conductive plate deactivates the resonator.

In some embodiments at least one of said electrically active components comprises an electro-active material adjacent to said resonator member, and said step of changing a control signal applied to said electrically active component comprises changing a biasing voltage applied across said electro-active material to changing the dielectric permittivity of said electro-active material.

In some embodiments, said method further comprises forming groups of said resonator members to control a frequency response of said resonator members within a same group in a same way.

In some embodiments, said method further comprises receiving a signal indicating a target frequency response; and determining from a data store storing frequency responses and corresponding control signals applied to said electro-active components for said apparatus the corresponding control signals to apply to said electro-active components to provide a frequency response at or close to said target frequency response and applying said control signals.

In some embodiments, said method further comprises: determining a frequency response of said apparatus on applying said control signals retrieved from said data store; and applying an amended at least one of said control signals and determining an updated frequency response; and continuing to amend and apply said at least one control signal and to determine said updated frequency responses until a frequency response sufficiently close to said target frequency response is obtained; and maintaining said updated control signals and update said data store.

In some embodiments, said method comprises on receiving a target frequency response: selecting a subset of said plurality of resonator members to activate or deactivate by controlling said switching mechanism associated with said subset to electrically connect or disconnect said subset of said plurality of resonators from said one of said conductive plates in order to set a frequency response of said apparatus close to said target frequency response, and where said frequency response is not within a threshold amount of said target frequency response; and controlling a biasing voltage applied to said electro-active material of said subset of activated resonator members to change a dielectric permittivity of said electro-active material to fine tune a frequency response of said apparatus.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims maybe combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION

Some example embodiments will now be described with reference to the accompanying drawings in which:

Fig. la illustrates a perspective view of an apparatus according to an embodiment;

Fig. ib illustrates a sideview of an apparatus according to an embodiment;

Fig. 2 illustrates a top view of a resonator apparatus where the resonator members are arranged in groups;

Fig. 3 shows the tuning affect of the groups of resonator members;

Fig. 4 shows the frequency variation of the apparatus where the number of open switches are changed;

Fig. 5 shows the variation in the unloaded Q-factor where the number of open switches are changed;

Fig. 6 shows a flow diagram of a method of tuning an RF filter according to an embodiment;

Fig. 7a shows a perspective view of the distributed resonator implemented with electroactive material;

Fig. 7b shows a cross section of an example embodiment of distributed resonators with electro-active material of tunable dielectric permittivity; Fig. 8 shows an example embodiment of an operation of a tunable RF filter based on dielectric permittivity tuned distributed resonators;

Fig. 9 shows the frequency variation as a function of the number of actuated resonator members of Fig. 8;

Fig. io shows the variation in the unloaded Q factor as a function of the number of actuated resonator members of Fig. 8;

Fig. n shows a three pole filter;

Fig. 12 shows a cross section through a tunable filter comprising both switches and electro-active materials.

Fig. 13 shows a flow diagram illustrating a method of operation of a tunable RF filter according to an example embodiment;

Fig. 14a, 14b shows a split distributed resonator apparatus according to an example embodiment;

Fig. 15 provides a graph illustrating the frequency tunability of the split resonator apparatus of Fig. 14;

Fig. 16 provides a graph illustrating changes in the Q factor of the split resonator apparatus of Fig. 14;

Fig. 17 shows an example embodiment of a tunable PCB based distributed resonator filter; and

Fig. 18 shows an example embodiment of the application of artificial intelligence to the distributed resonator filter of example embodiments.

DETAILED DESCRIPTION

Before discussing the example embodiments in any more detail, first an overview will be provided.

Some example embodiments are based on distributed resonators, and in some embodiments distributed split- resonator technology. In distributed resonators the frequency of operation is not a function of one resonant post, but of many resonant posts, suitably distributed in an array in the resonant chamber volume, allowing for improved compactness (lower height of the resonators) while still maintaining very good performance/high quality. In case of the split-distributed resonator based filters, the resonators rely not only on the coupling among the resonant posts, but the constituent elements of the resonant posts themselves are also made in the distributed form and the coupling between them can be varied. This, in comparison with the standard distributed resonator, caters for extremely low profiles, while allowing for a more uniform distribution of the electromagnetic fields inside the resonant cavity and hence higher unloaded quality factors.

Example embodiments allow for tuning by a) either making the individual or splitresonators switchable (activated or deactivated) providing relatively coarse frequency tuning, or b) tunable by application of Electro-Chromic or Liquid-Crystal material whose dielectric permittivity is controllable, providing relatively fine frequency tuning or c) combination of the above.

Embodiments provide the application of switches (PIN diode, MEMS, etc.) or electrically switchable material (Transition-Metal-Oxide (TM0)) to the individual or to the split resonators allowing them to be activated or deactivated either individually or on a split- resonator group level, in a way that is related to the currently required frequency response, which in a filter may be the passband of the filter. As will be shown below, a large tuning range can be achieved.

Additionally and/or alternatively embodiments provide the application of electro-active materials such as Electro-Chromic (EC) material or Liquid-Ciystal (LC) material.

These may be applied to the individual resonators or to the split-resonators in order to achieve the desired RF frequency tunability, again, either for individual resonators or for resonator groups. This technique may support a somewhat more limited tuning frequency range compared to the switching technique and is thus more suited for a finer RF tuning.

Combined application of both concepts and techniques of (sub-) resonator switching and (sub-) resonator RF tuning can be provided for filter coarse and fine tuning.

Methods of distributed or split- resonator based RF filter tuning for a) switched resonators, b) tuned resonators, and c) switched + tuned resonators are disclosed.

These ideas may be applied to different filters such as air cavity based resonator filters and PCB based resonator filters.

The control of the tuning properties may be enhanced by artificial intelligence techniques to provide self-tuning and self-optimization of the RF filters related to the specific applications. The technique provides an electrically active component associated with at least a subset of the resonator members and in some cases with all of the resonator members allowing the frequency response of that resonator to be adjusted under electrical, nonmechanical control thereby providing effective, robust and efficient control. This allows for the frequency response of the multiple resonator members to be controlled and provides e.g. a tunable distributed filter.

In some cases the electrically active component is arranged between the resonator member and one of the conductive plates thereby providing an effective way of controlling the electrical coupling between the resonator member and the conductive plate and thereby the frequency response of the resonator member. The electrically active component may be a switching mechanism or an electro-active material such as a liquid-Ciystal (LC) or Electro-Chromic (EC) material and in each case a biasing voltage across the electrical component may be used to change the electrical coupling, either by coupling the resonator member to the conductive plate and thereby activating it where the electrical active component is a switching mechanism or by changing the dielectric permittivity between the two when it is an electro-active material.

Where the electrically active component is a switching mechanism which couples the resonator member to the conductive plate then the other end of the resonator member may be remote from the other conductive plate.

In some embodiments, one end of the resonator member may have an electrically active component in the form of a switching mechanism to activate or deactivate the component while the other end may have the electroactive material whose dielectric permittivity changes with biasing voltage. In this way, a resonator member which can be activated or deactivated and one whose frequency response itself can be more finely tunned is provided. In some embodiments all of the resonator members may have an electrically active component which allows the resonator member to be activated or deactivated and another electrically active component which allows the resonator member’s frequency response to be more finely tuned. In this way, the filter formed by these resonators may be tuned in two stages. Firstly a coarse tuning stage may be performed to provide a frequency response close to the desired frequency response where a certain subset of the resonator are activated and then a more fine tuning may be performed where the dielectric permittivity of the activated resonator members is controlled to provide a frequency response closer to the desired frequency response. Tuning individual resonator members can require complex control circuitry and in some cases the resonator members may be arranged in groups with resonators in a same group being controlled together.

In some embodiments, the arrangement of the groups might be according to the geometric location of the resonator members such that central resonator member(s) may form one group with the closest resonator members to the central resonator member(s) forming in a subsequent group and then the next closest and so on. This may provide a filter with a simplified yet effective control.

In other embodiments, artificial intelligence may be used to help tune the filter to the desired frequency response. This may involve the frequency responses achieved with the electrically active components controlled in different ways being stored, such that over time the data store amasses many pairs of frequency responses and control configurations and these can be used as a starting point when a particular required frequency is requested. The stored data may be updated over time during operation of the filter. Detection circuitry associated with the filter can be used to determine the actual frequency response and the control parameters changed to make adjustments as required.

In some cases the resonator members are formed of conductive hollow elements such as metallic posts that are mounted on a conductive plate and extend towards another conductive plate.

In other embodiments, they may be arranged within a laminate structure and form conductive vias which are tubular holes within the laminate with the surfaces comprising electrically conductive material.

Where they are metallic posts then they may be housed within a cavity within a conductive housing.

In some embodiments, the posts may be split posts, that is they may be formed of a plurality of members arranged adjacent to each other such that combined they form a cylindrical post, each member forming a different cross section portion of the post. In some embodiments, there may be an electrically active component arranged between the plurality of members forming the cylindrical post. This may be a switch to connect the members, or it may be an electro-active material to change the dielectric permittivity between the members. In this way a spilt distributed filter is provided and a further means of controlling the frequency response by controlling the switches or the dielectric permittivity of the electro-active material between the members forming the post can be used.

Fig. la shows an example arrangement of 49 (7x7) distributed single pole resonator members 10, mounted in a cavity 20, each resonator member 10 being individually equipped with a switch 12. Fig. lb shows a cross section through six of the resonators of Fig.ia, each being equipped with a switch 12 and showing an indication of individual control voltage. For the sake of simplicity, the RF blocking in the signal feeds is not shown, but this would be present to inhibit the leakage of the RF signal out of the resonators and impede possible RF perturbation of the voltage control to the resonators which would adversely impact the performance. The housing comprising two conductive plates 22 connected to ground that enclose the resonant elements 10 within cavity 20.

The switches allow the resonators to be activated or deactivated individually or in groups allowing the RF passband of the filter formed by the resonator apparatus to be tuned over a wide frequency range. Switch technology can be based on PIN diodes or MEMS or electrically switchable material like e.g. TMO. Depending on the actual frequency band required, the respective resonators can be activated, using the switches 12.

In the example of Fig. 1 forty nine resonator elements and forty nine switches placed at one end of the elements are provided. Fig. 3 shows an example of the operation frequencies provided by the resonator elements where the cavity has the following dimensions: 5 x 5 x 0.25 mm³. In order to test frequency tunability, switches were kept initially closed and, then, they were sequentially opened in groups as shown in Fig. 2. Fig. 2 shows an example embodiment where the switches 12 and their corresponding resonant members 10 are divided into groups, 1-7, whereby in Figure 2 element 10(6) belongs to group 6 and element 10(7) belongs to group 7. The number of groups is equal to 7 (7x7 matrix)are divided into groups, 1-7. The number of groups is equal to 7 (7x7 matrix).

In this example embodiment, the grouping of the switches is done in the following way: the centre resonant element is designated to belong to group 1 and it is with reference to this element that the rest of the groups are formed. Group 2 is formed on the basis of physical proximity to the group 1. In this case, the 4 resonant elements that are closest and equidistant from the centre element are designated to belong to group 2. The second group of resonant elements are equidistantly positioned with respect to the centre element, but physically further away than the elements from group 2 with respect to the centre element these are group 3. Using a similar logic, the rest of the groups are obtained. Viewed in this way, one can think of the centre element (group 1) to be the “most significant bit”, while the elements of group 710(7) are the “least significant bits”.

By progressively and sequentially opening the switches, starting from group 1, the table of operational frequencies shown in Fig. 3 is obtained. It should be noted that switches do not need to be switched ON/OFF in the fashion presented here, but a different grouping logic can be used. However, the change in groupings would have no effect on the operational frequencies at the extremes (fully ON or fully OFF switches), instead its effect would be more pronounced on the exact values of the intermediate frequencies.

The table shown in Fig. 3 is plotted for better visualisation of Fig. 2. Element o: group 1; elements 1 - 4: group 2; elements 5 - 8: group 3; elements 9 - 16: group 4; elements 17 - 24: group 5; elements 25 - 36: group 6; elements 37 - 49: group 7. Furthermore, the table shows the related centre frequencies which are obtained by activating/ deactivating the respective resonators/resonator groups. As one can see from the results of the investigations depicted in the table, the resonator arrangement comprising 49 resonators can be tuned for this design between 26.5 GHz up to 169 GHz.

Fig. 4 graphically depicts the variation of frequency versus the number of open switches, based on the logic which has been just previously described, while Fig. 5 depicts the values of the unloaded Q factors vs the number of open switches.

Fig. 4 shows that the variation in the frequency of operation is between 169 GHz to 26.5 GHz, equivalent to a tunability of over 600 %. That is a huge range of coarse tuning which can be achieved by this example configuration. The values of the unloaded Q factors also vary as shown in Fig. 5, being highest for the highest frequencies of operation. They vary from 876 for the frequency of 169 GHz to 343 for 26.5 GHz in this example. This is expected due to the fact that the relative electrical cavity size is greatly reduced for lower frequencies which have a larger wavelength. Of course, this is only one example - the exact tuning values will depend on the design of the initial resonator, shown in Fig. 1.

Fig. 6 shows an example method of operation of a tunable distributed RF filter according to an example embodiment. Starting at step Sio where all resonators are deactivated, the target frequency of the application is then defined at step S20. Then in step S30, the required resonators/groups of resonators to be activated are selected so as to adjust the configuration to provide a frequency response close to the target frequency. The required distributed resonators/groups of resonators are activated in step S40, whereupon the system (e.g. RF frontend) can be put into operation at step S50. The system is kept in operation until at step S60 the system has to support a different target frequency. This requires the filter, based on the distributed resonators, to be re-configured. Where the target frequency changes, the method again starts with the identification and selection of the appropriate distributed resonators/groups of resonators to be activated or deactivated to support the new target frequency.

We note, that the configuration of distributed resonators shown in Fig. 1 is an example of one pole of a potential RF filter. Depending on the required performance of the filter (e.g. selectivity), several such example configurations maybe combined by for example mounting several distributed resonator groups within a single housing with walls between the groups, the walls having coupling irises (see for example Fig. 11).

In some example embodiments instead of applying switches to the resonators in order to activate or deactivate the resonators, RF tunable material such as Electro-Chromic (EC) material or Liquid-Ciystal (LC) can be used, which materials allow the dielectric permittivity to be controlled at the distributed resonators and thereby the RF characteristics of the distributed resonators and the resultant filter to be tuned.

Fig. 7a shows a perspective view of a 7X7 distributed resonator arrangement having resonator members 10 within cavity 20. The distributed resonator is similar to the distributed resonator of Fig.ia but with distributed EC and/or LC portions 14 forming the tunable portion of the resonator members 10 instead of having switches for tuning. Fig. 7(b) shows a cross section of the example embodiment of Fig. 7a with biasing control voltages used to control the dielectric permittivity of portions 14.

As shown in Fig. 7, EC- or LC material, allows the dielectric permittivity to be tuned by the application of suitable control voltages. This has been implemented between the top end (or bottom end) of the individual distributed resonator elements and the upper (or lower) cavity housing. By applying suitable control voltages to the EC or LC material mounted on the individual resonators, the dielectric permittivity and thus the RF characteristics of the EC and LC material and of the resonators can be controlled/tuned. In this way, the individual resonators and the filter resulting from the tunable distributed resonators can be tuned to support different RF target frequencies and/or different bandwidths.

A related example method of the inventive RF tunable distributed resonator filter concept is shown in Fig. 8.

Initially at step S100 all resonators are at an initial configuration e.g. with a defined dielectric permittivity applied to all distributed resonators. At step S200 a system target frequency is defined and the dielectric permittivities of the individual distributed resonators that are needed to meet the target frequency are determined at step S300. Subsequently, at step S400 the individual selected dielectric permittivities are applied to the individual resonators by application of the respective related control voltages. The system is then put into operation at step S500 and operated as long as the target frequency stays the same. If the target frequency is to be changed at step 600, the method returns to step S300 with the definition of a new target frequency. Although this method is shown for target frequencies it should be understood, that additionally or alternatively the passband bandwidth and/or the selectivity characteristics can be tuned using the control voltages.

Figs. 9 and 10 show the extent of dielectric tunability when the resonator is loaded with a commercially available LC material, E63. This material possesses a dielectric permittivity of 2.78 and loss tangent of 0.0076 in the non-actuated state and a dielectric permittivity of 3.23 and loss tangent of 0.0006 in the actuated state at mm- wave frequencies. For this purpose, the resonator with the same dimensions as the one shown in Fig. 1 is used. It is assumed, for the purpose of this figure that the LC material has a dielectric permittivity of 3 in the non-actuated state and a dielectric permittivity of 4 once actuated. Fig. 9 shows that the tunability of about 1 GHz is achieved with a resonator operating at a nominal frequency of 19.15 GHz, corresponding to an average frequency shift of about 20 MHz per step. In percentage terms, this corresponds to tunability of 0.1 % per actuated LC cell. It should be noted that the unloaded Q factor increases as frequency is reduced. This is due to the fact that the E63 LC mixture has higher losses in the activated state as opposed to the non activated state. Depending on the required performance of the filter realized by the tunable distributed resonators, several poles consisting of the basic concept/ configuration described above can be combined in a geometrical arrangement such as is shown in Fig. 11. That is multiple arrays of resonator members may be mounted between conductive plates and arranged within individual cavities, the linking walls of the cavities comprising coupling windows 25 allowing the signal to pass between the multiple resonator arrays. Each array is configured to provide a different pole or frequency response. Fig. 11 shows an example of a three-pole filter based on distributed resonator technology. A similar arrangement may be used to provide a multiple pole filter formed from split distributed resonators.

A further example embodiment is one where the two embodiments of switches and electro-active material are combined, to achieve a further improved tunable RF filter. An example implementation is shown in Fig. 12.

Fig. 12 shows a cross section of the distributed resonators forming a filter, with switches 12 and EC or LC layers 14 for tuning. The switches are used to activate and deactivate the individual resonators and are mounted at alternate resonators on alternate ends. The resonators lie between two conductive plates 22. The EC or LC layers 14 are in this embodiment at opposite ends to the switches 12 and each switch and each layer is controlled by an individual control voltage. As described above, the switchable and tunable distributed resonator filter can e.g. at first be coarse tuned by activating or deactivating the respective switches required in order to meet the range of the targeted RF carrier frequency. Subsequently, the filter can be fine tuned and optimized by tuning via the EC or LC segments at each resonator. In other embodiments the switches and EC and/or LC layers maybe at the same end.

Fig. 13 shows an exemplary method of operation related to a filter which can be controlled by switchable distributed resonators and tuned with respect to dielectric permittivity by EC or LC material associated with the resonators, as previously indicated by Fig. 12.

In Fig. 13 at step S205 the configuration of the filter is started by deactivating all resonators and setting the dielectric permittivity to a starting value. At step S210 a target frequency is defined. This may be the system setting the frequency for a particular mode of operation or an operator inputting a value or a signal received from elsewhere indicating a desired frequency band. At step S220 the resonators or group of resonators to be activated given the target frequency is determined, and they are then activated in step S230 by switching the associated switches. Then finer tuning is performed by determining at step S240 the expected required dielectric permittivities of the individual activated resonators and at S250 these are set by adjusting the control voltage across the EC and/or LC material. Operation of the system is then started at step S260 and is performed until a change of target frequency is received at step S270, this target frequency is defined at step S265 and at step S255 it is determined whether fine tuning using changes in the dielectric permittivities is sufficient to provide the change and if so the method proceeds to step S240. If a greater adjustment is required then the method proceeds to S220 where the resonators to be activated and deactivated are determined. As noted for Fig. 8 this method could also be used for tuning passband width and/or selectivity characteristics of the filter.

The determination of the resonators to be activated and the required dielectric permittivities for a particular target frequency may be retrieved from a data store associated with the filter, the data store being updated during operation with new data regarding target frequencies and dielectric permittivities and activated resonator members that generate particular frequency responses.

Fig. 14a and b show a tunable RF filter based on switchable and/or tunable split- distributed resonators. Fig. 14a shows the perspective view, while Fig. 14b shows a top view.

The apparatus of Fig. 14 provides a further variant of a split-distributed filter that provides a very low profile filter solution. Here the ideas of resonator switching and resonator tuning by EC or LC is applied to split-distributed resonator filters, and is combined with switches and/or EC and/or LC material placed in between the split segments to flexibly connect/disconnect (switches) the individual split segments of a resonator with each other or to tune (EC, LC) the split-segments of the resonators individually, both resulting in an further extended possibility of tuning.

In Fig. 14, the different possibilities of applying switches 12 and/or EC and/or LC material 14 to the split-resonators have been indicated individually on individual resonators 10 within cavity 20 for clarity. However, the two may be combined such that individual split-resonator segments may have both on-/off-switching, as well as individual split segment tuning using EC and/ or LC material 14 along with the possibility to connect individual split segments of a distributed resonator with each other, leading to several possibilities of switching and tuning per distributed resonator and thus to a highly flexible tuning of a filter realized based on such switchable and tunable split-distributed resonators. In some embodiments in addition to or as an alternative to having switches between the conductive plate and the split resonator, there may be switches between the split resonator members, allowing them to be shorted together.

Considering an example response based on the resonator depicted in Fig. 14: The example resonator comprises switching elements 12 placed on one end of the resonator elements 10 with a tunable dielectric material (LC and/ or EC) 14 sandwiched between the split posts of the split resonator elements. It has already been shown that switching itself can provide a wide tuning range, however, the granularity may be relatively poor. It has also been shown that the tunable LC and/ or EC material allow for very fine granularity at the expense of a lower tuning range. In the resonator of Fig. 14, we provide the means for both high tunability and high granularity. For example, for the case when all switches are closed in Fig. 14, the resonator operates at a frequency of 19 GHz, whereas, when the switches are open, the resonant frequency drops to 1.4 GHz. This provides for an average frequency step per open switch of about 0.55 GHz. Such a step is considered too high for many applications. However, the situation can be ameliorated by the addition of fine tuning provided using LC (or e.g. EC) material with the same characteristics as used in the previous example. For this purpose, let us assume that all switches are open and that fine tuning needs to be provided using LC only. Although the example of Fig. 14 shows the switches at one end and the tunable dielectric material between the split resonators, in other embodiments, the arrangement may differ and comprise switches between the elements and/ or tunable dielectric material at an end of the resonator members.

Fig. 15 shows an example of the tuning frequency as a function of the actuated LC cells, while Fig. 16 shows an example of the variation of obtained Q factors as functions of the number of activated LC cells.

Fig. 15 shows that the tunability from the nominal frequency of 1.457 GHz to 1.396 GHz is achieved. This corresponds to the tunable range of 61 MHz, which is equivalent to 1.84 MHz per actuated LC cell. We note that the unloaded Q factor increases as the frequency decreases; this is due to the fact that the loss tangent of the E63 LC mixture exhibits a lower loss tangent in the actuated state than in the non-actuated state. A further example embodiment provides a tunable PCB-based RF filter based on switchable and tunable distributed resonators.

While the previous example embodiments of the highly tunable filter are based on air cavity distributed resonators, these ideas of distributed resonator filter tuning can also be applied to PCB-based embodiments, as shown in Fig. 17. Fig. 17 shows a cross section of a section of a filter having two distributed resonators 10. As in the case of the air cavity variants, switches 12 have also been implemented for the PCB variant, allowing to individually switch-on or switch-off the resonators, the switches 12 being controlled by respective individual control voltages. As in Fig. 7, RF blocking is not shown in the voltage control feeds. Furthermore, EC and/or LC material 14 is implemented at the one end of the resonator, along with additional layers such as an electrode layer and layers for biasing the electrode layers, allowing control of the EC/LC layers 14 and thus tuning of the individual resonators 10.

The resonators 10 are vias within laminate 30 sandwiched between an upper conductive plate 22A and a lower conductive plate 22B. The via is formed of a conductive layer connected to the top and bottom conductive plates 22A , 22B respectively by switches 12. The electro-active material 14 is at one end of the resonator between the conductive layer forming the via and the laminate. There is a low conductivity conductor with a high skin depth 32 between the electro-active material and the laminate 30. There is also a spacer dielectric 34 that is inactive that contacts the electro-active material and runs to the conductive plate and has a high conductivity conductor 38 with a low skin depth between it and the laminate 30. As for the switches 12, individual control voltages for controlling the EC/LC layers 14 have also been provided.

In this way, a PCB-based counterpart to the switchable and tunable air cavity filter described previously is achieved. As in the air cavity case, coarse tuning of the PCB- based distributed resonator filter can be achieved by on-/off-switching of the respective resonators to meet the RF carrier frequency range and a fine tuning of the RF characteristic can be achieved by EC/LC tuning.

As for the air cavity filter, it is also possible to apply only distributed resonator switching or only distributed resonator tuning for the PCB-based filter variant. A further example embodiment uses artificial intelligence for self -tuning and - optimization.

With distributed resonators having many resonator members, and with the possibility of both switches, electro-active material and split resonator members, the tuning control can become very complex. In order to support advanced operation, tuning and optimization of such potentially complex configurations, there is proposed the application of artificial intelligence for self -control, -tuning and -optimization. As schematically shown in Fig. 18, an artificial intelligence routine has been added to the control of a tunable distributed resonator filter. Parameters/info provided to the Al unit are target parameters such as a target frequency and/or passband bandwidth of the system, for which the distributed resonator based filter has to be tuned and optimized for. The actual output frequency characteristic of the filter is determined and is fed to the Al unit allowing the Al unit to monitor the filter performance/characteristic/output signal and thus enable filter tuning and optimization to meet the previously defined target performance using a feedback routine. Outputs of the Al unit may include the control signals for controlling the switching and tuning voltages (VTctrln and VSctrln) on an individual or at least group level.

One point to note is that the implementation of switches and/or electro-active material that enables tuning of dielectric permittivity may add some additional insertion loss to the tunable filter compared to the non-tunable version. However, the amount of additional insertion loss is an additional design parameter, which can e.g. be controlled by the number of distributed resonators which are equipped with switches and/ or EC and/ or LC material. If the maximum possible filter tunability is not required from an application point of view, only a certain number of distributed resonators may be equipped with switches and/ or EC or LC material, which should reduce the additional filter insertion loss.

In summary embodiments seek to provide compact highly tunable RF filter, which may have the following benefits:

■ Wide range of frequency tunability,

■ limited complexity to achieve tunability,

■ reduced system design effort,

■ compact size, ■ cost effectiveness,

■ enable improved sustainability, versatility and flexibility of systems by use of tunable filters,

■ enable realization of multiband/software defined radio systems in a beneficial manner with reduced complexity,

■ reduced tuning and control effort by self-tuning and self-optimization related to the respective RF bands currently to be addressed.

A person of skill in the art would readily recognize that steps of various abovedescribed control methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machineexecutable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices maybe, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description maybe used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. An apparatus comprising: multiple resonator members arranged in an array between two conductive plates; at least one electrically active component associated with at least a subset of said resonator members, said at least one electrically active component being arranged between said two conductive plates and adjacent to or forming a part of said associated resonator member; and a controller for controlling an electrical characteristic of said at least one electrically active component and thereby changing a frequency response of said associated resonator member; said controller being configured to change a frequency response of said apparatus by controlling said frequency response of said at least a subset of said resonator members.

2. An apparatus according to claim 1, wherein said at least one electrically active component comprises at least one of: a switching mechanism configured to connect or disconnect said resonator member from one of said conductive plates; and an electro-active material adjacent to said resonator member, changing in a biasing voltage applied to said electro-active material changing the dielectric permittivity of said electro-active material.

3. An apparatus according to any preceding claim, wherein at least a first subset of said multiple resonator members comprise a switching mechanism arranged between said resonator member and one of said conductive plates, said switching mechanism being configured to electrically connect or disconnect said resonator member from said one of said conductive plates in response to a control signal from said controller.

4. An apparatus according to any preceding claim, wherein at least a second subset of said multiple resonator members each comprise said electrically active component as an end portion adjacent to one of said conductive plates and comprising an electroactive material, said controller being configured to control a biasing voltage applied to said electro-active material to change a dielectric permittivity of said electro-active material.

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5. An apparatus according to claim 3 and claim 4, wherein said at least a first and at least a second subset comprise a same at least a subset of said multiple resonator members, such that said resonator members in said at least a subset comprise one of said switching mechanisms to connect one end of said resonator member to one of said conductive plates and one end of said resonator member comprises an electro-active material.

6. An apparatus according to claim 4 or 5, wherein said electro-active material comprises at least one of a liquid crystal material and an electro-chromic material

7. An apparatus according to any preceding claim, wherein said multiple resonator members are arranged in an array and said controller is configured to form groups of said resonator members to control a frequency response of said resonator members within a same group in a same way.

8. An apparatus according to any preceding claim, wherein said resonator members comprise vias within a laminate structure, said laminate structure being held between said conductive plates.

9. An apparatus according to any one of claims 1 to 7, wherein said resonator members comprise posts arranged in a cavity formed by a conductive housing, said conductive housing comprising said conductive plates.

10. An apparatus according to claim 9, wherein said resonator members are mounted to form a plurality of substantially cylindrical posts, at least some of said substantially cylindrical posts comprising a plurality of resonator members each resonator member forming a portion of said substantially cylindrical post, said plurality of resonator members forming a cylindrical post being mounted adjacent but separate to each other.

11. An apparatus according to claim 10, wherein at least a subset of said cylindrical posts each comprises an electrically active component arranged between said resonator members forming said cylindrical post.

12. An apparatus according to any preceding claim, said apparatus further comprising: a data store configured to store frequency responses and corresponding control signals applied to said electro-active components for said apparatus; wherein said controller is configured to: receive a signal indicating a target frequency response; determine from said data store the corresponding control signals to apply to said electro-active components to provide a frequency response at or close to said target frequency response.

13. An apparatus according to claim 12, said apparatus further comprising: circuitry for detecting a frequency response of said apparatus; wherein said controller is configured to determine said frequency response of said apparatus on applying said control signals retrieved from said data store; and to amend at least one of said control signals and determine an updated frequency response; and to continue amending said at least one control signal and determining said updated frequency responses until a frequency response sufficiently close to said target frequency response is obtained; and to maintain said updated control signals and update said data store.

14. An apparatus according to any preceding claim, said apparatus comprising multiple resonator members arranged in at least two arrays between said two conductive plates, said at least two arrays forming separate linked resonator apparatus, said apparatus comprising a signal path for a signal to pass between said at least two arrays; wherein at least one of said electrically active components is associated with each of at least a subset of said resonator members in each of said at least two arrays; and said controller is configured to change a frequency response of said apparatus by separately controlling said frequency response of said at least a subset of said resonator members in each of said at least two arrays, such that a frequency response of said two resonator apparatus are controlled independently of each other.

15. A method of tuning a frequency response of an apparatus according to any preceding claim comprising: for a plurality of resonator members, changing a control signal applied to at least one electrically active component associated with said plurality of resonator members and thereby changing an electrical response of said plurality of resonator members.