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Title:
SOLID DIELECTRIC RESONATOR, HIGH-POWER FILTER AND METHOD
Document Type and Number:
WIPO Patent Application WO/2019/154496
Kind Code:
A1
Abstract:
A solid dielectric resonator (12) configured to operate in one or more modes in conjunction with a coaxial transmission line (9), and a method (1900) for coupling energy to the solid dielectric resonator (12). The solid dielectric resonator (12) comprises: a ceramic block covered by a conductive coating (13), having an uncovered area (14) in the conductive coating (13) on the side of the solid dielectric resonator (12) facing the coaxial transmission line (9). The uncovered area (14) in the conductive coating (13) enables energy of the coaxial transmission line (9) to be coupled magnetically to the solid dielectric resonator (12) in a resonant mode.

Inventors:
GUESS, Michael (Huawei Technologies Sweden AB Skalholtsgatan 9, Kista, 16440, SE)
Application Number:
EP2018/053153
Publication Date:
August 15, 2019
Filing Date:
February 08, 2018
Export Citation:
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Assignee:
HUAWEI TECHNOLOGIES CO., LTD. (Huawei Administration Building Bantian Longgang District, Shenzhen, Guangdong 9, 518129, CN)
GUESS, Michael (Huawei Technologies Sweden AB Skalholtsgatan 9, Kista, 16440, SE)
International Classes:
H01P1/20; H01P1/203; H01P5/08; H01P7/10
Foreign References:
US20040119564A12004-06-24
US20050099242A12005-05-12
US20160126622A12016-05-05
US20120206213A12012-08-16
Other References:
None
Attorney, Agent or Firm:
KREUZ, Georg (Huawei Technologies Duesseldorf GmbH, Riesstr. 8, Munich, 80992, DE)
Download PDF:
Claims:
CLAIMS

1. A solid dielectric resonator (12) configured to operate in one or more modes in conjunction with a coaxial transmission line (9), external to and electrically isolated from the solid dielectric resonator (12); wherein the solid dielectric resonator (12) comprises:

a closed cavity covered by a conductive coating (13), having an opening (14) in a first plane of the conductive coating (13), wherein the first plane is parallel with a second plane outside the closed cavity, which second plane comprises the coaxial transmission line (9), and wherein the opening (14) in the conductive coating (13) enables energy from an electromagnetic field generated by the coaxial transmission line (9) to be coupled magnetically to a resonant mode generated inside the closed cavity of the solid dielectric resonator of the solid dielectric resonator (12).

2. The solid dielectric resonator (12) according to claim 1 , wherein the opening (14) in the first plane of the conductive coating (13) is arranged as at least one slot, extending substantially perpendicular to the coaxial transmission line (9) of the second plane.

3. The solid dielectric resonator (12) according to any one of claim 1 or claim 2, wherein the opening (14) in the first plane of the conductive coating (13) comprises at least one slot extending substantially perpendicular to the coaxial transmission line (9), and one slot extending substantially in parallel with the coaxial transmission line (9).

4. The solid dielectric resonator (12) according to any one of claims 1-3, wherein the opening (14) in the first plane of the conductive coating (13) comprises a conductive element (22).

5. The solid dielectric resonator (12) according to claim 4, wherein the conductive element (22) is isolated from the conductive coating (13) by a by an area of removed conductive coating.

6. The solid dielectric resonator (12) according to any one of claims 4-5 wherein the opening (14) in the first plane of the conductive coating (13) comprises two substantially perpendicular slots having a common intersection, which common intersection comprises the conductive element (22).

7. The solid dielectric resonator (12) according to any one of claims 1-6 wherein the opening (14) in the first plane of the conductive coating (13) is separated from the coaxial transmission line (9) by a Printed Circuit Board and an air gap. 8. The solid dielectric resonator (12) according to any one of claims 4-7, wherein the conductive element (22) is arranged in the slot substantially parallel with the coaxial transmission line (9).

9. The solid dielectric resonator (12) according to any one of claims 1-8, wherein the conductive coating (13) and / or the conductive element (22) comprises a metal plating.

10. A high-power filter (180), comprising:

a plurality of solid dielectric resonators (12), according to any one of claims 1-9; a coaxial transmission line (9), connecting the plurality of solid dielectric resonators (12).

1 1. A method (1900) for manufacturing a solid dielectric resonator (12), according to any one of claims 1-9, which method (1900) comprises:

applying (1901 ) a conductive coating (13) on a closed cavity;

creating (1902) an opening (14) in a first plane of the conductive coating (13); arranging (1903) a coaxial transmission line (9) in a second plane, external to the solid dielectric resonator (12), which is parallel with the first plane of the conductive coating (13);

arranging (1904) a dielectric medium between the first plane of the conductive coating (13) of the closed cavity, and the second plane comprising the coaxial transmission line (9).

Description:
SOLID DIELECTRIC RESONATOR, HIGH-POWER FILTER AND METHOD

TECHNICAL FIELD

Implementations described herein generally relate to a solid dielectric resonator configured to operate in one or more modes in conjunction with a coaxial transmission line, external to and electrically isolated from the solid dielectric resonator.

BACKGROUND

As radios become more compact and integrated there is renewed demand to produce low- loss, high-power filters that are low volume or have a small form-factor. Primarily, this is to enable components to be packed tightly and used in conjunction with large antenna arrays for Multiple Input Multiple Output (MIMO) systems. Prior to final assembly in such a radio system, the filter component requires configuration in the form of frequency and bandwidth alignment, so that it meets the required specification.

One solution for producing low-loss, small filters, is to use solid dielectric multi-mode resonator filters. These comprise several multi-mode resonators, with each resonator coupling energy to the next resonator by means of an inter-resonator coupling elements that are formed as integral physical features in the part.

After manufacture, many identical filters are fitted into a system housing, connecting to adjacent power amplifying components and antenna components. The simplest way to successfully manufacture these assemblies in high volume is to provide connectors on all three components. The filter can then be connected to the amplifier Printed Circuit Board (PCB), the antenna sub-assembly, in turn, connected to the filter. Although effective, this method introduces additional loss and significant expense in the many connectors required. An alternative is to use a metal pin soldered in the filter and separately soldered to the amplifier circuit board at one end, and the antenna sub-assembly at the other. This method, however, is prone to mechanical failure over time, owing to significantly different rates of thermal expansion and contraction of the solder joint, the pin and the circuit boards. Furthermore, it is difficult to inspect the quality of the solder joint on the pin, owing to it being hidden underneath the filter when attached to the board.

In addition to the stated assembly issues, using a pin within the ceramic filter creates other manufacturing concerns and tolerance issues. For example, the position, diameter and depth of the pin is controlled by a drilled hole. This is typically machined in the green - or pre-fired - state. All three parameters can vary during the firing process, as the part shrinks, resulting in deviation from the intended performance. The complexity of the parts also means that deviation occurs in secondary variables as a result of variation in a first parameter.

The drilled hole must also be completely covered or filled with a highly conductive coating. In order to ensure adequate coating, the hole must also be of sufficient size to avoid air bubbles restricting the flow of the coating on application. This requirement conflicts with the general demand to miniaturise the filter.

The use of a metallic probe to couple energy into a microwave filter is well-known to those skilled in the art. In a cavity filter, the probe inserts into the air space internal to the resonator. In a solid resonator, the probe is formed by the inclusion of a typically cylindrical feature in the material of the resonator that is produced by moulding or drilling. The cylindrical void is then conductively coated to provide the complete probe, with an area of no conductive coating around the end of the probe, to provide insulation from the electrical ground, formed on the exterior of the resonator completely covered in conductive coating.

The probe couples energy into a resonant mode of the block, with the electrical field vector being co-axial with the probe and the magnetic field being circumferential about the pin.

The strength or magnitude of the input coupling can be measured in a variety of ways. One figure of merit for a one-port measurement of the coupled energy is the reflected group delay. A lower group delay corresponds with a greater input coupling. Greater input coupling enables a larger overall filter bandwidth for a given return loss and, conversely, a narrow band filter requires a smaller input coupling, for a given return loss.

When designing the probe, the length is practically limited by the diameter of the hole, otherwise conductively coating the hole during manufacture is difficult. Even for weak coupling, the physical size of the hole requires space within the resonator and contributes several variables to be controlled and considered in the manufacturing tolerance stack-up.

After manufacture, the filter must be connected to the rest of the system - namely the antenna and power amplifier. This may typically be achieved in two ways. The first is to use a separate, physical connector, such a Quick disconnect SubMiniature version A (QMA), or similar, soldered to the filter. This then pushes or screws to a receptacle on the PCB. This method provides the highest reliability, as the filter can move sufficiently and independently of the board during thermal expansion. It is also the most expensive method, requiring additional parts and their fitting. Additional space in the system must also be provided to accommodate the connectors.

The alternative is to directly solder the filter to the PCB or PCBs that host the amplifier and antenna. This requires a solder joint between the ground on the filter and the ground on the PCB, as well as a second solder joint, between the probe metallisation and a track on the PCB that carries the signal. This is a significantly cheaper and lower volume solution, but suffers from requiring the joining of several different materials that have vastly different coefficients of thermal expansions (solder, ceramic, ceramic metallisation, PCB copper, PCB substrate). Inspection of joint after manufacture is difficult and, after many temperature cycles, the solder joint itself will crack owing to the fatigue of the joint from the Coefficient of Thermal Expansion (CTE) mismatch.

It would be desired to realise a solid dielectric resonator, not suffering from the enumerated disadvantages, and also requiring less space.

SUMMARY

It is therefore an object to obviate at least some of the above mentioned disadvantages and to improve the performance in a high power filter.

This and other objects are achieved by the features of the appended independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, a solid dielectric resonator is provided. The solid dielectric resonator is configured to operate in one or more modes in conjunction with a coaxial transmission line, external to and electrically isolated from the solid dielectric resonator. The solid dielectric resonator comprises a closed cavity covered by a conductive coating. The conductive coating has an opening in a first plane of the conductive coating. The first plane is parallel with a second plane outside the closed cavity, which second plane comprises the coaxial transmission line. The opening in the conductive coating enables energy from an electromagnetic field generated by the coaxial transmission line to be coupled magnetically to a resonant mode generated inside the closed cavity of the solid dielectric resonator of the solid dielectric resonator.

Thanks to the provided solution, a solid dielectric resonator is provided, without any inserted pin. Thereby, the solid dielectric resonator could be fixed directly to a dielectric substrate such as a PCB. Thus, the previously mentioned problems associated with using a pin within the ceramic filter are omitted, leading to a solid dielectric resonator less prone to mechanical failure, which is easier and thereby cheaper to produce. Also, a more compact filter, occupying less space may be constructed, which is attractive from e.g. a design point of view.

In an implementation of the solid dielectric resonator according to the first aspect, the opening in the first plane of the conductive coating may be arranged as at least one slot, extending substantially perpendicular to the coaxial transmission line of the second plane.

The at least one slot may be applied symmetrically in relation to the distant coaxial transmission line in some embodiments.

Thereby an improved solid dielectric resonator is provided, having an opening which is rather easy to manufacture.

In yet an implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the opening in the first plane of the conductive coating may comprise at least one slot extending substantially perpendicular to the coaxial transmission line, and one slot extending substantially in parallel with the coaxial transmission line.

Thereby yet an improved solid dielectric resonator is provided, having an opening which is rather easy to manufacture.

Further, by applying a plurality of slots, the respective length of each involved slot may be reduced, which may be an advantage when space is limited on the mounting board, or when an alternative is required to avoid unwanted couplings or resonances caused by a particular slot/dielectric/substrate combination.

In yet an implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the opening in the first plane of the conductive coating may comprise a conductive element.

By applying the conductive element inside the opening in the resonator, the maximum possible coupling is increased.

In yet an implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the conductive element may be isolated from the conductive coating by a by an area of removed conductive coating.

Thereby, further implementation details are described in order to improve the solid dielectric resonator. In another an implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the opening in the first plane of the conductive coating may comprise two substantially perpendicular slots having a common intersection, which common intersection comprises the conductive element. Thereby, the maximum possible coupling is further increased. Further, the described implementation may be applied when size is important or spurious couplings and resonances are problematic.

In a further implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the opening in the first plane of the conductive coating is separated from the coaxial transmission line by a Printed Circuit Board (PCB) and an air gap.

In yet an implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the conductive element may be arranged in the slot substantially parallel with the coaxial transmission line.

In another an implementation of the solid dielectric resonator according to the first aspect, or according to any implementation thereof, the conductive coating and / or the conductive element comprises a metal plating. Thereby, further implementation details are described in order to improve the solid dielectric resonator.

According to a second aspect, a high-power filter is provided. The high-power filter comprises a plurality of solid dielectric resonators, according to the first aspect, or any implementation thereof. Further, the high-power filter comprises a coaxial transmission line, connecting the plurality of solid dielectric resonators.

Thanks to the provided solution, a high-power filter is provided, without any inserted pin into solid dielectric resonators of the high-power filter. Thereby, the solid dielectric resonator could be fixed directly to a dielectric substrate such as a PCB. Thus, the previously mentioned problems associated with using a pin within the ceramic filter are omitted, leading to a solid dielectric resonator less prone to mechanical failure, which is easier and thereby cheaper to produce. Also, a more compact filter, occupying less space may be constructed, which is attractive from e.g. a design point of view.

According to a third aspect, a method is provided for manufacturing a solid dielectric resonator according to the first aspect, or any implementation thereof. The method comprises applying a conductive coating on a closed cavity. Further, the method comprises creating an opening in a first plane of the conductive coating. Also, the method furthermore comprises arranging a coaxial transmission line in a second plane, external to the solid dielectric resonator, which is parallel with the first plane of the conductive coating. The method additionally comprises arranging a dielectric medium between the first plane of the conductive coating of the closed cavity, and the second plane comprising the coaxial transmission line.

Thanks to the provided solution, a method of manufacture of a solid dielectric resonator is provided, without requiring any inserted pin into the solid dielectric resonator. Thereby, the solid dielectric resonator could be fixed directly to a dielectric substrate such as a PCB. Thus the previously mentioned problems associated with using a pin within the ceramic filter are omitted, leading to a solid dielectric resonator less prone to mechanical failure, which is easier and thereby cheaper to produce. Also, a more compact filter, occupying less space may be constructed, which is attractive from e.g. a design point of view.

Other objects, advantages and novel features of the aspects of the invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are described in more detail with reference to attached drawings in which:

Figure 1 illustrates a useful dual-mode electromagnetic field configurations, according to an example.

Figure 2 illustrates magnetic fields of the transmission line (into the page) providing the signal and the coupled mode inside the resonator.

Figure 3A illustrates a single slot in ceramic resonator with transmission line coupling, according to an example.

Figure 3B illustrates a single slot in ceramic resonator with transmission line coupling, according to an example.

Figure 3C illustrates a single slot in ceramic resonator with transmission line coupling, according to an example.

Figure 4 illustrates a reflected group delay/ input coupling for various lengths of a single slot, according to an example.

Figure 5 illustrates a double slot in ceramic resonator with transmission line coupling, according to an example.

Figure 6 illustrates a reflected group delay/ input coupling for various lengths of a double slot, according to an example.

Figure 7 illustrates a maximum input coupling (reflected group delay) versus slot length for single and dual slots, according to an example.

Figure 8 illustrates a single slot coupling with surface director for increasing coupling, according to an example.

Figure 9 illustrates a slot and director formed on ceramic by selective removal of conductive coating, according to an example.

Figure 10 illustrates a magnetic field configuration for slot coupling using transmission line and conductive director, according to an example.

Figure 11 illustrates a reflected group delay /input coupling for various lengths of a single slot with 3 mm director, according to an example.

Figure 12 illustrates a maximum input coupling versus slot length for various director lengths, according to an example. Figure 13 illustrates a double slot coupling with surface director for increasing coupling, according to an example.

Figure 14 illustrates a reflected group delay/ input coupling for various lengths of a double slot with 1 1 mm director, according to an example.

Figure 15 illustrates a maximum input coupling versus slot length for various director lengths, according to an example.

Figure 16 illustrates an example of an embodiment in full filter.

Figure 17 illustrates an example of an embodiment, showing only circuit board assembly and bottom surface of conductive coating on filter, according to an embodiment of the invention.

Figure 18 illustrates an example of an embodiment, showing only circuit board assembly and bottom surface of conductive coating on filter (top view).

Figure 19 is a flow chart illustrating a method according to an embodiment of the inv- ention.

DETAILED DESCRIPTION

Embodiments of the invention described herein are defined as a solid dielectric resonator, a high-power filter and a method for manufacturing a solid dielectric resonator, which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be limited to the examples set forth herein; rather, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the herein disclosed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

Figure 1 is a schematic illustration over Magnetic and Electric field vectors for orthogonal modes in a solid dielectric multimode resonator 12. The dimensions of the part and the dielectric properties of the material may be chosen to determine the resonance frequency of each mode, where each mode is orthogonal to the next.

The embodiments disclosed herein provide a means to couple energy into one of the resonant modes of the filter. It may be applicable to all cases of mode usage in the resonator 12 without limitation, but examples in this document will be shown for use in dual-mode resonators 12, where it is deemed most useful and practical. These are shown in an example of a standard configuration in Figure 1.

The dielectric resonator 12 comprises a piece of dielectric (i.e. nonconductive) material, such as e.g. ceramic, that is designed to function as an electro-magnetic resonator in radio-frequency, microwave bands. The microwaves are confined inside the resonator material by the abrupt change in permittivity and/or conductivity at the surface, and bounce back and forth between the sides. At certain frequencies, the resonant frequencies, the microwaves form standing waves in the resonator 12, oscillating with large amplitudes. The dielectric resonator 12 may comprise a block of ceramic that has a large dielectric constant and a low dissipation factor. The resonant frequency is determined by the overall physical dimensions of the resonator 12 and the dielectric constant of the material. The dielectric resonator 12 may be used as bandpass filters and/or in conjunction with antennas.

There are three types of resonant modes that can be excited in the dielectric resonator 12: transverse electric, transverse magnetic and/or hybrid electromagnetic modes. Theoretically, there is an infinite number of modes in each of the three groups, and desired mode may be selected based on application requirements.

Whereas the prior art described energy being coupled using an inserted probe along the axis of the electric field vector of the coupled mode, here, the energy is coupled magnetically to the orthogonal mode, from an adjacent, but otherwise unconnected, transmission line.

Rather than requiring a physical protrusion into the cavity, an opening in the conductive ground plane is instead provided to allow the magnetic fields of the transmission line to transfer to the resonator 12, thereby effecting the coupling. These fields are shown in Figure 2.

The details of this are provided below, but the key features are that the coupled mode is orthogonal to the coupled mode using a pin and that no direct connection between signal paths are required to achieve the coupling. Instead only the ground planes of the signal transmission line and the resonator 12 need to be connected. The transmission line may terminate in a short circuit where only one filter is connected, or can continue to subsequent filters where multiplexing is required. All examples in this document assume a short-circuit termination of the line, for simplicity, but no limitation is implied.

Thereby, embodiments of the invention enable a solid dielectric resonator 12 to be fixed directly to a PCB, using only the ground plane as the electrical connection.

The signal path from adjacent components may be carried on a PCB track and couple magnetically through and to metallic features on the surface of the resonator 12. By this means, no direct physical connection is required on the signal path, eliminating a point of failure at a solder joint or a costly and bulky component, where a connector is used.

The exterior ground area requires the only physical connection. Here, manufacturing can be easily done using existing planar multi-layer PCB methods to connect the resonator 12 to the board with glue, and chemical plating to provide the ground connection. Alternatively, a single solder joint on the ground only (not the signal path) can be used and also inspected.

Figure 3A depicts a single slot in ceramic resonator 12 with transmission line coupling, according to an embodiment. A coaxial transmission line 9 carrying a signal and terminating, in some embodiments, in a short circuit at one end 10. The line can be in air, or some other dielectric substrate 11 such as PCB, provided that there is a ground plane provided.

The solid dielectric resonator 12 is completely covered in conductive coating 13, except for an uncovered area or opening 14, which in the illustrated embodiment comprises a slit, perpendicular to the direction of the transmission line 9, but parallel to the magnetic fields of both the line 9 and the intended mode to be coupled to.

The resonator 12 is electrically attached to the top surface of the transmission line ground 15, where an identical slot may be cut in some embodiments, allowing the transmission line 9 to be seen. The attachment can be made by solder joint or, if the assembly is made as part of a multi-layer PCB, by a glued PCB that is subsequently copper-plated to connect the grounds. A physical connection between the transmission line signal path 9 and the resonator 12 is not required; i.e. the resonator 12 and the transmission line signal path 9 are electrically isolated from each other.

The slot width of the opening 14 may with advantage be as small as possible to enable magnetic flux to pass whilst still being possible to manufacture. This may e.g. be about 10% of the shortest resonator dimension, but other dimensions can be made to work, where spurious transmissions or resonance are avoided.

In other embodiments, the opening 14 may have another shape, different from a slit, and / or elongated in another direction than perpendicular to the direction of the transmission line 9. Some arbitrary examples are illustrated in Figure 3B and Figure 3C.

The optional short-circuit termination 10 at one end of the transmission line 9 can be provided by metal plating, soldering, plated through vias, or any other practical means, provided good electrical contact is made.

Although the width of the track will also affect the resultant coupling, this can be fixed to match a convenient impedance for the signal transmission line 9.

The required coupling to the resonator 12 can then be achieved by varying the length of the opening 14, from zero / no coupling, to the maximum length of the resonator 12/ maximum coupling. The resultant coupling is similar to that obtained by the pin (according to prior art) and is shown for comparison and various slot lengths in Figure 4.

Figure 5 illustrates another embodiment of the resonator 12. The opening 14 in this embodiment, comprises a first slot 16, and a second slot 17, which are separated by a gap 18, which gap 18 comprises conductive coating 13.

The first slot 16 may ideally be offset in the opposite direction to the second slot 17, so that they are symmetrically positioned. The two slots 16, 17 may be parallel and typically, but not necessarily, of equal length. The gap 18 between the slots 16, 17 can be any size practical such that two distinct slots are retained, and is ideally as small as possible to reduce spurious coupling. The resultant coupling for the case where both slots 16, 17 are equal is shown in Figure 6. Although the maximum possible coupling is very similar to that possible with the first embodiment, it can be seen that all other coupling values are achieved with much smaller slots 16, 17. This may be of particular usefulness when space is limited on the mounting board, or when an alternative is required to avoid unwanted couplings or resonances caused by a particular slot / dielectric/ substrate combination.

A direct comparison of slot length versus coupling is shown for single and dual slots in Figure 7.

A limitation of the previously described embodiments, compared to the inserted probe according to the conventional solutions, is the natural restriction on the maximum coupling possible with the slot when at maximum slot length. An improvement can be made by reducing the distance between the transmission line 9 and the opening 14, i.e. the slot opening (i.e. the thickness of the substrate), but this has practical limitations determined by the manufacturing process.

A third embodiment, which overcomes this limitation on maximum coupling, without requiring a reduction in the transmission line spacing, is shown in Figure 8.

Here, the opening 14 of the resonator 12 comprises a slot 19 of removed metallisation, which is removed from both the resonator coating 20 and the transmission line ground plane, as in previously illustrated embodiments. However, an additional area 21 of metal is removed from the conductive coating 20 of the resonator 12 to produce a small conductive element 22 open-circuit at each end. The element 22 may be substantially perpendicular to the slot 19 of the opening 14, and substantially parallel to the transmission line 9 and may serve as a field director to enable a greater coupling of the magnetic fields between the transmission line 9 and resonator 12. The slot and director pattern on the resonator 12 is shown in Figure 9 and the field resultant field configurations are shown in Figure 10.

The director length may be chosen in conjunction with the slot length so as to provide the required input coupling without any spurious resonances or couplings occurring for a given combination of geometry and materials.

The width of the coupling should be similar to the width of the perpendicular slot, and typically slightly smaller to minimise the overall size of the coupling structure and filter. The area of removed metallisation around the slot may be chosen to avoid spurious couplings and unnecessary loss, whilst being practical to produce. As the feature does not need to be repeated on the mounting surface, a gap of <0.5mm may be possible.

The operation of the coupling may otherwise be as previously, with the slot length determining the overall coupling for a given director length. This can be seen in Figures 11 , where input coupling is shown for various slot lengths, for director lengths of 3mm.

Figure 12 shows the maximum input coupling possible versus slot length for a variety of director lengths. It can be seen that the maximum possible coupling is greatly increased over previous embodiments.

A fourth embodiment is a combination of the previously described embodiment two and three, and is shown in Figure 13. Here, a director 22 is utilised in conjunction with a double slot, forming an opening 14. The implementation of both director 22 and dual slots 14 may be performed as described in the previous embodiments.

This combination allows for a slight increase in the overall maximum coupling possible, but also provides alternative combinations for achieving the same coupling, where size is important or spurious couplings and resonances are problematic.

The function of the coupling structure can be seen to be similar to previous embodiments and is shown in Figure 14 for a director length of 1 1 mm.

The maximum coupling for a given slot length is shown for various director lengths in Figure 15. It is evident that very strong couplings, comparable to those of long conductive probes, can be provided but without any protrusion into the cavity of the resonator 12.

An example of an embodiment of the invention is shown implemented in a full filter assembly in Figure 16.

A version of the same assembly is also shown in Figure 17. This embodiment realises a strongly-coupled fourth-order filter, directly mounted on to a circuit board, without a physical connection to the signal path. It can be seen that, by using a multi-layer PCB 23, formed e.g. by two bonded copper- plated substrates, a suspended coaxial transmission line 9 can be routed from the two board inputs 25/26. By utilising cut-outs in the copper 27, on various layers, and by forming plated through-vias 28, the ground planes can be connected to form one single ground plane. Furthermore, the plated through-vias 28 can be used to provide the short-circuit terminations 29 of the transmission line 9 after the input coupling slots 30, which may be applied in this design example.

In this example, the opening in the ground on the circuit board 23 is larger than the slots on the ceramic. This is acceptable as the conductive coating on the ceramic 31 provides the ground once joined to the PCB 23 and eliminates alignment errors.

The director 22 and opening 14, which may comprise a slot pattern, on the conductive coating 31 of the ceramic can be seen more clearly in relation to the transmission line 9 in Figure 18.

Figure 19 is a flow chart illustrating embodiments of a method 1900 for manufacturing a solid dielectric resonator 12. The method 1900 aims at manufacturing the previously described solid dielectric resonator 12.

To appropriately control the analogue beam-steerable phased-array antenna, the method 1900 may comprise a number of method steps 1901-1904. It is however to be noted that any, some or all of the described steps 1901-1904, may be performed in a somewhat different chronological order than the enumeration indicates, be performed simultaneously or in a somewhat adjusted order according to different embodiments. Further, it is to be noted that some method steps may be performed in a plurality of alternative manners according to different embodiments, and that some such alternative manners may be performed only within some, but not necessarily all embodiments. The method 1900 may comprise the following steps:

Step 1901 comprises applying a conductive coating 13 on a closed cavity.

The closed cavity may comprise a ceramic block which may be cubic, cuboidic, parallelepipedic, rhombohedronic, hexahedronic, polyhedronic, etc. The conductive coating 13 may comprise a thin layer of metal such as e.g. copper, silver, etc. Step 1902 comprises creating an opening 14 in a first plane of the conductive coating 13.

The opening 14 may be created by removing a subset of the applied 1901 conductive coating 13 of the closed cavity. The conductive coating 13 may be removed by laser, in some embodiments.

The opening 14 may for example comprise one singular, or a plurality of slots, extending substantially perpendicular to the coaxial transmission line 9. The opening 14 may have many different shapes in different embodiments, such as e.g. a plus sign like shape wherein one of the slots is extending substantially in parallel with the coaxial transmission line 9; or an H-like shape wherein one of the slots is extending substantially in parallel with the coaxial transmission line 9.

In some embodiments, the opening 14 in the conductive coating 13 comprises a conductive element 22. The conductive element 22 may comprise a piece of conductive coating 13 which has not been removed from the closed cavity. Thus, the conductive element 22 may be isolated from the conductive coating 13 by a by an area of removed conductive coating 13. Thereby, the conductive element 22 comprises an island of conductive material inside the opening 14.

In yet some embodiments, the opening 14 in the first plane of the conductive coating 13 comprises two substantially perpendicular slots having a common intersection, which common intersection comprises the conductive element 22.

Step 1903 comprises arranging a coaxial transmission line 9 in a second plane, external to the solid dielectric resonator 12, which is parallel with the first plane of the conductive coating 13.

Step 1904 comprises arranging a dielectric medium between the first plane of the conductive coating 13 of the closed cavity, and the second plane comprising the coaxial transmission line 9.

The dielectric medium may comprise e.g. a PCB layer and/or an air layer.

Thanks to the provided method, the previously described problems associated with using a metal pin soldered in the filter and separately soldered to the amplifier circuit board at one end, and the antenna sub-assembly at the other. Tolerance issues, positioning, and problems associated with diameter and depth of the pin are completely avoided, as the pin is omitted. It is also possible to make a smaller filter than when using a prior art ceramic filter with an inserted pin.

The terminology used in the description of the embodiments as illustrated in the accompanying drawings is not intended to be limiting of the described solid dielectric resonator 12, high-power filter 180, and method 1900. Various changes, substitutions and / or alterations may be made, without departing from the invention as defined by the appended claims.

As used herein, the term "and / or" comprises any and all combinations of one or more of the associated listed items. In addition, the singular forms "a", "an" and "the" are to be int erpreted as“at least one”, thus also possibly comprising a plurality of entities of the same kind, unless expressly stated otherwise. It will be further understood that the terms "includes", "comprises", "including" and / or "comprising", specifies the presence of stated features, actions, integers, steps, operations, elements, and/ or components, but do not preclude the presence or addition of one or more other features, actions, integers, steps, operations, elements, components, and / or groups thereof. A single unit such as e.g. a processor may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/ distributed on a suitable medium, such as an optical storage medium or a solid- state medium supplied together with or as part of other hardware, but may also be distributed in other forms such as via Internet or other wired or wireless communication system.