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Title:
MULTIMODE RADIO FREQUENCY RESONATOR
Document Type and Number:
WIPO Patent Application WO/2017/215739
Kind Code:
A1
Abstract:
A multimode radio frequency resonator (100) is described. The multimode radio frequency resonator (100) comprises a monoblock (102) of dielectric material, a conductive layer (104) covering the monoblock (102), and a first non-conductive elongated slot (106) in the conductive layer (102), the first non-conductive elongated slot (106) having a first length (108) and a first width (110) together defining a first slot surface (112), wherein the monoblock (102) has a first surface area (126) covered by the conductive layer (104), the first surface area (126) extending along at least a part of the first length (108) and protruding in relation to the first slot surface (112). A method (200) for tuning such a multimode radio frequency resonator (100) is also described.

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Inventors:
GUESS MICHAEL (SE)
CUI ZHENG (SE)
Application Number:
PCT/EP2016/063624
Publication Date:
December 21, 2017
Filing Date:
June 14, 2016
Export Citation:
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Assignee:
HUAWEI TECH CO LTD (CN)
GUESS MICHAEL (SE)
CUI ZHENG (SE)
International Classes:
H01P7/10
Foreign References:
US20050128031A12005-06-16
US6002307A1999-12-14
US20160094265A12016-03-31
US4691179A1987-09-01
Other References:
None
Attorney, Agent or Firm:
KREUZ, Georg (DE)
Download PDF:
Claims:
CLAIMS

1. A multimode radio frequency resonator (100) comprising

a monoblock (102) of dielectric material,

a conductive layer (104) covering the monoblock (102), and

a first non-conductive elongated slot (106) in the conductive layer (102), the first non- conductive elongated slot (106) having a first length (108) and a first width (1 10) together defining a first slot surface (1 12),

wherein the monoblock (102) has a first surface area (126) covered by the conductive layer (104), the first surface area (126) extending along at least a part of the first length (108) and protruding in relation to the first slot surface (1 12).

2. The multimode radio frequency resonator (100) according to claim 1 , wherein the multimode radio frequency resonator (100) has at least a first mode (1 a) and a second mode (2a), wherein the first length (108) of the first non-conductive elongated slot (106) is parallel with a magnetic field vector of the first mode (1 a).

3. The multimode radio frequency resonator (100) according to claim 1 or 2, wherein the monoblock (102) comprises a first ridge (130) or a first trench (146), wherein the first surface area (126) is arranged on a first sidewall (152) of the first ridge (130) or the first trench (146), the first sidewall (152) of the first ridge (130) or first trench (146) being arranged adjacent to and facing the first non-conductive elongated slot (106).

4. The multimode radio frequency resonator (100) according to claim 3, wherein the monoblock (102) comprises a second surface area (128) covered by the conductive layer (104), the second surface area (128) extending along at least a part of the first length (108) on the opposite side of the first non-conductive elongated slot (106) in relation to the first surface area (126), wherein the first surface area (126) and the second surface area (128) together with the first slot surface (1 12) form a first trench (146). 5. The multimode radio frequency resonator (100) according to claim 4, comprising a second ridge (132), wherein the second surface area (128) is arranged on a first sidewall (154) of the second ridge (132), the first sidewall (154) of the second ridge (132) facing the first non- conductive elongated slot (106); or

wherein the second surface area (128) is arranged on a second sidewall (156) of the trench (146), the second sidewall (156) of the trench (146) facing the first non-conductive elongated slot (106).

6. The multimode radio frequency resonator (100) according to anyone of the preceding claims, wherein the ratio between the first length (108) of the first non-conductive elongated slot (106) and the first width (1 10) of the first non-conductive elongated slot (106) is at least 2, preferably at least 5, and most preferred at least 10.

7. The multimode radio frequency resonator (100) according to claim 6, wherein the first non- conductive elongated slot (106) is curved.

8. The multimode radio frequency resonator (100) according to any of the preceding claims, wherein the first surface area (126) has an extension perpendicular to the first slot surface

(1 12) in the interval 0.05 mm to 2 mm.

9. The multimode radio frequency resonator (100) according to any of the preceding claims, wherein the first surface area (126) is perpendicular to the first slot surface (1 12).

10. The multimode radio frequency resonator (100) according to anyone of the preceding claims, comprising

a second non-conductive elongated slot (134) in the conductive layer (104), the second non-conductive elongated slot (134) having a second length (136) and a second width (138) together defining a second slot surface (140), and

wherein the monoblock (102) has a third surface area (142) covered by the conductive layer (104), the third surface area (142) extending along at least a part of the second length (136) and protruding in relation to the second slot surface (140). 1 1 . The multimode radio frequency resonator (100) according to claim 10, wherein the second length (136) of the second non-conductive elongated slot (134) is parallel with a magnetic field vector of the second mode (2a).

12. The multimode radio frequency resonator (100) according to claim 10 or 1 1 , wherein the monoblock (102) comprises a third ridge (150) or a second trench (148), wherein the third surface area (142) is arranged on a first sidewall (158) of the third ridge (150) or the second trench (148), the first sidewall (158) of the third ridge (150) or the second trench (148) being arranged adjacent to and facing the second non-conductive elongated slot (134). 13. The multimode radio frequency resonator (100) according to claim 12, wherein the monoblock (102) comprises a fourth surface area (144) covered by the conductive layer (104), extending along at least a part of the second length (136) on the opposite side of the second non-conductive elongated slot (134) in relation to the third surface area (142), wherein the third surface area (142) and the fourth surface area (144) together with the second slot surface (140) form a second trench (148). 14. The multimode radio frequency resonator (100) according to anyone of claims 10-13, comprising a first main surface (114), a second main surface (116), a third main surface (118), a fourth main surface (120), a fifth main surface (122), and a sixth main surface (124), wherein the first non-conductive elongated slot (106) is arranged on the first main surface (106), and the second non-conductive elongated slot (134) is arranged on the second main surface (116), wherein the second main surface (1 16) is located adjacent to the first main surface (114).

15. Communication device (300) for a wireless communication system (400), the communication device (300) comprising a multimode radio frequency resonator (100) according to any of the preceding claims.

16. Method (200) for tuning a multimode radio frequency resonator (100) comprising

a monoblock (102) of dielectric material, and

a conductive layer (104) covering the monoblock (102),

wherein the monoblock (102) has a first main surface (1 14) and a first surface area (126) covered by the conductive layer (104), the first surface area (126) protruding in relation to the first main surface (1 14), the method (200) comprising

removing (502) the conductive layer (104) from a first slot surface (1 12) to form a first non-conductive elongated slot (106), having a first length (108) and a first width (110), the slot surface (1 12) extending along the first surface area (126).

Description:
Multimode radio frequency resonator Technical field

The present invention relates to a multimode radio frequency resonator and to a method for tuning such a multimode radio frequency 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 tightly packed and used in conjunction with large antenna arrays for 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. Frequency adjustment in radio-frequency and microwave filters for cellular communications has typically required a solid conducting rod or screw used to perturb the electric or magnetic fields within the interior of the resonator itself. For the case of a solid dielectric resonator, this has required holes to be formed within the resonator itself, in order to accommodate said conducting tuning element. This is undesirable owing to the added manufacturing complexity and the resultant increase in total volume, owing to the removal of high-dielectric material. More importantly, for multi-mode dielectric resonators used in a functional microwave or Radio Frequency (RF) filter, using conducting elements to perturb the Electromagnetic (EM) field of a resonator results in more than just the desired mode frequency being adjusted. Orthogonal modes coexisting in the same multi-mode section are simultaneously and non-linearly adjusted in frequency whilst the desired mode is tuned. Further, orthogonal modes can become increasingly coupled together - where their energy is shared or transferred - making further independent control impossible. Alternative, non- intrusive methods to negate these issues have further problems. For many cases, the above problems make the accurate configuration and integration of solid dielectric multi-mode filters very difficult and have precluded their wider adoption in commercial radio systems. Summary

An object of the present invention is to provide a multimode radio frequency resonator which at least partially resolves one of the problems of the prior art.

Another object of embodiments of the present invention is to provide a multimode radio frequency resonator which is easily tunable. Another object of embodiments of the present invention is to provide a multimode radio frequency resonator in which the different modes may be tuned independently of each other.

Another object of embodiments of the present invention is to provide a method for tuning a multimode radio frequency resonator.

According to a first aspect a multimode radio frequency resonator is provided, the multimode radio frequency resonator comprising a monoblock of dielectric material, a conductive layer covering the monoblock, and a first non-conductive elongated slot in the conductive layer, the first non-conductive elongated slot having a first length and a first width together defining a first slot surface, wherein the monoblock has a first surface area covered by the conductive layer, the first surface area extending along at least a part of the first length and protruding in relation to the first slot surface. The conductive layer is formed of a highly conductive material. The highly conductive material could be a metal.

The first surface area covered by the conductive layer provides an additional electrical ground plane that is external to the resonator. This can be compared to conventional resonators, where the electrical ground is provided exclusively by the interior surface of the conductive coating. Adjustment of a resonator or series of resonators can be made externally and prior to placement within a larger assembly, owing to the self-shielding properties provided by embodiments of the invention. The first surface area provides an additional, carefully designed, electrical ground plane that is external to the resonator.

The self-shielding properties provided by the first surface area can be shown to minimise the energy radiated from the first non-conductive elongated slot such that the multimode radio frequency resonator can be placed within an assembly, or otherwise in proximity to another component, without further substantially adjusting the frequency of the resonant modes of the first multimode radio frequency resonator. As stated above the energy radiated from the tuning features is minimized with the provision of the first surface area. Thus, any features close to the multimode radio frequency resonator will only have a weak field to interact with.

The self-shielding properties of the multimode radio frequency resonator also enable similar multimode radio frequency resonators to be placed in close proximity to each other, as is required in a commercial system, whilst minimising the transmission of energy from one multimode radio frequency resonator filter to an adjacent multimode radio frequency resonator. The features therefore allow for the multimode radio frequency resonators to be tuned and placed whilst maintaining the integrity of the signals in independent multimode radio frequency resonator. That is to say, the features enable good isolation between the signal of a first multimode radio frequency resonator and those of adjacent multimode radio frequency resonators.

Embodiments of the design will be shown to be at least compatible with three-axis machining but, more importantly, to be compatible with high-volume, moulded manufacturing methods such as, but not limited to, single axis isostatic-pressing, die-pressing, vacuum forming, super- plastic forming, injection-moulding, 3D printing, etc.

In addition to at least diminishing the technical problems with conventional technology, the multimode radio frequency resonator according to the first aspect also greatly simplifies production complexity and cost and thus enables more complex, compact and cost-effective full-system assembles based on these components to be designed and manufactured.

In a first possible implementation form of a multimode radio frequency resonator according to the first aspect, the multimode radio frequency resonator has at least a first mode and a second mode, wherein the first length of the first non-conductive elongated slot is parallel with a magnetic field vector of the first mode. This enables coupling or radiating of the first mode through the first slot and the first surface area to free air (or in general the outside of the resonator) providing an additional, carefully designed, electrical ground plane on the outside of the resonator. The strength of the coupling will depend on the length of the first non- conductive elongated slot. The resonance frequency of the multimode radio frequency resonator will depend on the strength of the coupling. Thus, when making the first non- conductive elongated slot longer the tuning of the frequency becomes stronger.

In a second possible implementation form of a multimode radio frequency resonator according to the first implementation form of the first aspect or to the first aspect as such, the monoblock comprises a first ridge or a first trench, wherein the first surface area is arranged on a first sidewall of the first ridge or the first trench, the first sidewall of the first ridge or first trench being arranged adjacent to and facing the first non-conductive elongated slot. A first ridge or a first trench is easily machinable in a monoblock. In a third possible implementation form of a multimode radio frequency resonator according to the second implementation form of the first aspect, the monoblock comprises a second surface area covered by the conductive layer, the second surface area extending along at least a part of the first length on the opposite side of the first non-conductive elongated slot in relation to the first surface area, wherein the first surface area and the second surface area together with the first slot surface form a first trench. By having a first surface area on one side of the first elongated slot and a second surface area on the opposite side of the first non-conductive elongated slot the first non-conductive elongated slot will be arranged in a trench. This will make the external ground plane symmetrical, which will be advantageous from an electrical field point of view.

A fourth possible implementation form of a multimode radio frequency resonator according to the third implementation form of the first aspect, comprises a second ridge, wherein the second surface area is arranged on a first sidewall of the second ridge, the first sidewall of the second ridge facing the first non-conductive elongated slot; or the second surface area is arranged on a second sidewall of the trench, the second sidewall of the trench facing the first non- conductive elongated slot. This is an easily machinable implementation form.

In a fifth possible implementation form of a multimode radio frequency resonator according to anyone of the first to fourth implementation forms of the first aspect or to the first aspect as such, the ratio between the first length of the first non-conductive elongated slot and the first width of the first non-conductive elongated slot is at least 2, preferably at least 5, and most preferred at least 10. The preferred first length will depend on the frequency required. The length should be longer than the first width to effect a change, but does not necessarily have an upper limit other than when the desired frequency is reached or when the first length is equal to the extension of the multimode radio frequency resonator. Another important feature is that the width of the first elongated elongated slot is sufficiently narrow to minimize the coupling of energy from any other mode than the mode having a magnetic field vector parallel to the length of the first non-conductive elongated slot, whilst still effecting change in the first mode.

In a sixth possible implementation form of a multimode radio frequency resonator according to the fifth implementation form of the first aspect, the first non-conductive elongated slot is curved. By having a curved first non-conductive elongated slot it is enabled to position the first non-conductive elongated slot on a surface of the monoblock on which the magnetic field vector of the first mode is circular, i.e. a surface of the monoblock on which the electric field vector of the first mode is perpendicular. By enabling the use of a first non-conductive elongated slot more freedom is provided in designing the multimode radio frequency resonator. A curved first non-conductive elongated slot for a first mode can be combined with a straight non-conductive elongated slot on the same side of the monoblock for a second mode. Thus, only one side of the monoblock may have to be machined.

In a seventh possible implementation form of a multimode radio frequency resonator according to any of the first to sixth implementation forms of the first aspect or to the first aspect as such, the first surface area has an extension perpendicular to the first slot surface in the interval 0.05 mm to 2 mm. If the extension is made smaller than 0.05 mm the effect from the first surface area will be impractically small. On the other hand, increasing the extension perpendicular to the first slot surface of the first area above 2 mm will have a negligible effect on the effect from the first surface area. Also, an extension perpendicular to the first slot surface of the first area above 2 mm will be more problematic to design and manufacture. This is a design trade-off. Thus, increasing the extension of the first surface area perpendicular to the first slot surface will not give any useful effect on the electromagnetic coupling but will make manufacturing more difficult.

In an eighth possible implementation form of a multimode radio frequency resonator according to any of the first to seventh possible implementation forms of the first aspect or to the first aspect as such, the first surface area is (at least essentially) perpendicular to the first slot surface. Such an arrangement of the first surface area minimizes the distance between the top of the first surface area and the slot surface, which may maximize the effect of the self- shielding. However, having the first surface area perpendicular to the first slot surface limits the available methods of manufacturing. As an example, pressing with a mould requires a small angle from perpendicular in order to let the mould release from the multimode radio frequency resonator.

A ninth possible implementation form of a multimode radio frequency resonator according to any of the first to eighth implementation forms of the first aspect or to the first aspect as such, comprises a second non-conductive elongated slot in the conductive layer, the second non- conductive elongated slot having a second length and a second width together defining a second slot surface, and wherein the monoblock has a third surface area covered by the conductive layer, the third surface area extending along at least a part of the second length and protruding in relation to the second slot surface. Such a second non-conductive elongated slot enables further tuning of another mode (e.g. a second mode) in the multimode radio frequency resonator in addition to the tuning effected by first non-conductive elongated slot (on the first mode). In a tenth possible implementation form of a multimode radio frequency resonator according to the ninth possible implementation form of the first aspect, the second length of the second non-conductive elongated slot is parallel with a magnetic field vector of the second mode. By arranging the second non-conductive elongated slot in this way it is enabled to tune the frequency of the second mode by tuning of the length of the second non-conductive elongated slot.

In an eleventh possible implementation form of a multimode radio frequency resonator according to the ninth or tenth possible implementation form of the first aspect, the monoblock comprises a third ridge or a second trench, wherein the third surface area is arranged on a first sidewall of the third ridge or the second trench, the first sidewall of the third ridge or the second trench being arranged adjacent to and facing the second non-conductive elongated slot. This is an easily machinable implementation form. In a twelfth possible implementation form of a multimode radio frequency resonator according to the eleventh possible implementation form of the first aspect, the monoblock comprises a fourth surface area covered by the conductive layer, extending along at least a part of the second length on the opposite side of the second non-conductive elongated slot in relation to the third surface area, wherein the third surface area and the fourth surface area together with the second slot surface form a second trench. By having the third surface area on one side of the second elongated slot and the fourth surface area on the opposite side of the second non- conductive elongated slot the second non-conductive elongated slot will be arranged in a trench. This will make the external ground plane symmetrical, which will be advantageous from an electrical field point of view.

A thirteenth possible implementation form of a multimode radio frequency resonator according to any of the ninth to the twelfth possible implementation forms of the first aspect comprises a first main surface, a second main surface, a third main surface, a fourth main surface, a fifth main surface, and a sixth main surface, wherein the first non-conductive elongated slot is arranged on the first main surface, and the second non-conductive elongated slot is arranged on the second main surface, wherein the second main surface is located adjacent to the first main surface. By configuring the first non-conductive elongated slot and the second non- conductive elongated slot on different surfaces the mutual interference between the first non- conductive elongated slot and the second non-conductive elongated slot will be minimized.

According to a second aspect a communication device for a wireless communication system is provided. The communication device comprises a multimode radio frequency resonator according to any of the first to thirteenth implementation forms of the first aspect or to the first aspect as such.

According to a third aspect a method is provided for tuning a multimode radio frequency resonator comprising a monoblock of dielectric material, and a conductive layer covering the monoblock, wherein the monoblock has a first main surface and a first surface area covered by the conductive layer, the first surface area protruding in relation to the first main surface, the method comprising removing the conductive layer from a first slot surface to form a first non-conductive elongated slot, having a first length and a first width, the slot surface extending along the first surface area.

The first surface area covered by the conductive layer provides an additional electrical ground plane that is external to the resonator. This can be compared to conventional resonators, where the electrical ground is provided exclusively by the interior surface of the conductive coating. Adjustment of a resonator or series of resonators can be made externally and prior to placement within a larger assembly, owing to the self-shielding properties provided by the invention. The first surface area provides an additional, carefully designed, electrical ground plane that is external to the resonator. The self-shielding properties provided by the first surface area can be shown to minimise the energy radiated from the first non-conductive elongated slot such that the multimode radio frequency resonator can be placed within an assembly, or otherwise in proximity to another component, without further substantially adjusting the frequency of the resonant modes of the first multimode radio frequency resonator. As stated above the energy radiated from the tuning features is minimized with the provision of the first surface area. Thus, any features close to the multimode radio frequency resonator will only have a weak field to interact with.

The self-shielding properties of the multimode radio frequency resonator also enable similar multimode radio frequency resonators to be placed in close proximity to each other, as is required in a commercial system, whilst minimising the transmission of energy from one multimode radio frequency resonator filter to an adjacent multimode radio frequency resonator. The features therefore allow for the multimode radio frequency resonators to be tuned and placed whilst maintaining the integrity of the signals in independent multimode radio frequency resonator. That is to say, the features enable good isolation between the signal of a first multimode radio frequency resonator and those of adjacent multimode radio frequency resonators. The resonance frequency of the first mode depends on the length of the first non-conductive elongated slot which is formed by removing the conductive layer from a first slot surface to form the first non-conductive elongated slot. The removal of the conductive layer may be performed in steps until the desired resonance frequency is achieved.

In a first implementation form of a method according to the third aspect, the multimode resonator has at least a first mode and a second mode, wherein the removal of the conductive layer is performed with the first length of the first non-conductive elongated slot parallel with a magnetic field vector of the first mode.

In a second implementation form of a method according to the first implementation form of the third aspect or to the third aspect as such, the ratio between the first length of the first non- conductive elongated slot and the first width of the first non-conductive elongated slot is at least 2, preferably at least 5, and most preferred at least 10. By having such a ratio, the tuning of only one of the modes is possible. Ultimately, the first length depends on how much tuning that is necessary. Thus, the length of the first non-conductive elongated slot is ultimately limited only by the size of the multimode resonator. The width of the first non-conductive elongated slot is preferably sufficiently small to not effect any other mode in the multimode resonator. In a third implementation form of a method according to the second implementation form of the third aspect, the removal is performed along a curve so that the resulting first non-conductive elongated slot is curved. This enables tuning of a mode on a side of the multimode resonator where the magnetic field of the first mode is circular at the surface. In a fourth implementation form of a method according to any of the first to third implementation forms of the third aspect or to the third aspect as such, the monoblock has a second main surface and a third surface area covered by the conductive layer, the third surface area protruding in relation to the first main surface, the method comprising removing the conductive layer from a second slot surface to form a second non-conductive elongated slot, having a second length and a second width, the slot surface extending along the third surface area. By removal of the conductive layer from said second slot surface to form the second non- conductive elongated slot also a second mode can be tuned.

In a fifth implementation form of a method according to the fourth implementation form of the third aspect, the removal of the conductive layer from the second slot surface is performed so that the length of the second non-conductive elongated slot is parallel with a magnetic field vector of the second mode. Thus an efficient tuning of the second mode is enabled. Short description of the drawings

Fig. 1 shows the electrical and magnetic vectors for a first mode in a multimode radio frequency resonator according to an embodiment of the invention.

Fig. 2 shows the electrical and magnetic vectors for a second mode in the multimode radio frequency resonator of Fig. 1 . Fig. 3 shows the electrical and magnetic vectors for a third mode in the multimode radio frequency resonator of Fig. 1 .

Fig 4 is a side view of the multimode radio frequency resonator of Fig. 1 and shows the electric field lines from the slot.

Fig. 5 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention.

Fig. 6 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention.

Fig. 7 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention. Fig. 8 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention.

Fig. 9 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention.

Fig. 10 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention.

Fig. 1 1 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention. Fig. 12 is a perspective view of a multimode radio frequency resonator according to another embodiment of the invention.

Fig. 13 shows in a side view the multimode radio frequency resonator of Fig. 10.

Fig. 14 shows the resonance frequency for the first mode as a function of the slot length in a multimode radio frequency resonator as shown in Fig. 1 when the resonance frequency of the second and third mode are equal. Fig. 15 shows the resonance frequency for the first mode as a function of the slot length in a multimode radio frequency resonator as shown in Fig. 1 when the resonance frequency of the second mode differs from the resonance frequency of the third mode.

Fig. 16 shows an assembly with multimode radio frequency resonators in close proximity to an external cover.

Fig. 17 shows the power radiated from a slot in Fig. 1 as a function of the distance between the surface areas for different heights of the surface area from the slot surface. Fig. 18 shows the change in resonant frequency of a multimode radio frequency resonator according to Fig. 1 as a function of the distance for the slot surface to the external cover for different heights of the surface area over the slot surface.

Fig. 19 shows schematically a communication device in a wireless communication system.

Detailed description

Below a description of embodiments will follow. In the following description of embodiments of the invention the same reference numerals will be used for the same or equivalent features in the different drawings.

Figs. 1-3 shows a multimode radio frequency resonator 100 comprising a monoblock 102 of dielectric material. A conductive layer 104 covers the monoblock 102. A first non-conductive elongated slot 106 is arranged in the conductive layer 104. The first non-conductive elongated slot 106 has a first length 108 and a first width 1 10, which together define a first slot surface 1 12. Fig. 4 is a side view of the multimode radio frequency resonator 100 of Figs. 1 -3 and also shows the electric field lines 190 emitted from the first non-conductive elongated slot 106. The monoblock 102 has a first surface area 126 also covered by the conductive layer 104. The first surface area 126 extends along at least a part of the first length 108 (Fig. 4) and protrudes in relation to the first slot surface 1 12.

The multimode radio frequency resonator 100 has a first mode shown in Fig. 1 , a second mode shown in Fig. 2 and a third mode shown in Fig. 3. The first mode has electric field vectors along a direction depicted by E1 and magnetic field vectors as depicted by M1 in Fig. 1. The second mode has electric field vectors along a direction depicted by E2 and magnetic field vectors as depicted by M2 in Fig. 2. The third mode has electric field vectors along a direction depicted by E3 and magnetic field vectors as depicted by M3 in Fig. 3. The first length 108 of the first non-conductive elongated slot 106 is parallel with the magnetic field vector M1 of the first mode.

In order to avoid too much reference numerals in all drawings, reference will now be made only to Fig. 3. The features shown in Fig. 3 are present also in Figs. 1 and 2 which show the same embodiment as Fig. 3. The monoblock 102 comprises a first ridge 130 and a second ridge 132. The first ridge 130 and the second ridge 132 together define a first trench 146. The first surface area 126 is arranged on a first sidewall 152 of the first ridge 130. The first sidewall 152 of the first ridge 130 is arranged adjacent to and facing the first non-conductive elongated slot 106. The second surface area 128 is arranged on a second sidewall 154 of the second ridge 132, the first sidewall 154 of the second ridge 132 facing the first non-conductive elongated slot 106.

The multimode radio frequency resonator 100 comprises a first main surface (or side) 1 14, a second main surface (or side) 1 16, a third main surface (or side) 1 18, a fourth main surface (or side) 120, a fifth main surface (or side) 122, and a sixth main surface (or side) 124. The first non-conductive elongated slot 106 is arranged on the first main surface 1 14 with the first ridge 130 and the second ridge 132 on opposite sides of the first non-conductive elongated slot 106. The multimode radio frequency resonator 100 also comprises a second non- conductive elongated slot 134 arranged on the second main surface 1 16, wherein the second main surface 1 16 is located adjacent to the first main surface 1 14. The second non-conductive elongated slot 134 has a second length 170 and a second width 138. A third ridge 160 and a fourth ridge 162 are arranged on opposite sides of the second non-conductive elongated slot 134. A third surface area 174, facing the second non-conductive elongated slot 134 and covered by the conductive layer 104, is arranged on the third ridge 160 and a fourth surface area 176, facing the second non-conductive elongated slot 134 and covered by the conductive layer 104, is arranged on the fourth ridge 162. The multimode radio frequency resonator 100 also comprises a third non-conductive elongated slot 164 arranged on the third main surface 1 18, wherein the third main surface 1 18 is located adjacent to the first main surface 1 14. A fifth ridge 166 and a sixth ridge 168 are arranged on opposite sides of the third non-conductive elongated slot 164. The third non-conductive elongated slot 164 has a third length 172. A fifth surface area 178, facing the third non-conductive elongated slot 164 covered by the conductive layer 104, is arranged on the fifth ridge 166 and a sixth surface area 180, facing the third non- conductive elongated slot 164 covered by the conductive layer 104, is arranged on the sixth ridge 168.

The first length 108 of the first non-conductive elongated slot 106 is at least partially parallel with the magnetic field vector M1 of the first mode. The second length 170 of the second non- conductive elongated slot 134 is at least partially parallel with the magnetic field vector M2 of the second mode. The third length 172 of the third non-conductive elongated slot 164 is at least partially parallel with the magnetic field vector M3 of the third mode. The electric field vector E1 of the first mode is orthogonal to the electric field vector E2 of the second mode. The electric field vector E3 of the third mode is orthogonal to the electric field vector E1 of the first mode and the electric field vector E2 of the second mode.

The view in Fig. 4 is taken towards the second main surface 1 16 and shows the electrical field lines 190 coming out of the first non-conductive elongated slot 106. As can be seen in Fig. 4 the field lines from most of the first non-conductive elongated slot 106 are bent towards the first surface area 126 and the second surface area 128. Only from the centre of the first non- conductive elongated slot 106 the field lines 190 are not bent towards any of the first surface area 126 and the second surface area 128. Such field lines 190 from the centre of the first non-conductive elongated slot 106 will end in other parts of the conductive layer 104 or in an adjacent external cover 228 (Fig. 16) as will be described below with reference to Fig. 15 and Fig. 16. Hence, the first surface area 126 and the second surface area 128 form an additional external ground plane. As most of the electric field lines end in the external ground plane formed by the first surface area 126 and the second surface area 128, only a small portion of the electric field is effected by an additional (external) conductive surface close to the multimode radio frequency resonator 100. This will be described in further detail below with reference to Fig. 16. This self-shielding of the first non-conductive elongated slot 106 is an important feature. The extension h perpendicular to the first slot surface 1 12 of the first ridge 130 and the second ridge 132 is shown in Fig. 4. The corresponding extension of the third ridge 160, the fourth ridge 162, the fifth ridge 166 (Fig. 3) and the sixth ridge 168 are the same as the extension h perpendicular to the first slot surface of the first ridge 130. The ridges 130, 132, 160, 162, 166, 168, should ideally be formed so that symmetry is preserved in the plane of both axes of the non-conductive elongated slots 106, 134, 164. This serves to reduce or preclude undesirable coupling between orthogonal modes that may otherwise occur as a result of including asymmetrically-place protrusions. As an example the first surface area 126 and the second surface area 128 both have an extension perpendicular to the first slot surface 1 12 in the interval 0.05 mm to 2 mm. If the extension h is made smaller than 0.05 mm the effect from the first surface area 126 and the second surface area 128 will be impractically small. On the other hand, increasing the extension h perpendicular to the first slot surface 1 12 of the first surface area 126 and the second surface area 128 above 2 mm will have a negligible effect. Also, an extension h perpendicular to the first slot surface 1 12 of the first area 126 and the second surface area 128 above 2 mm will be more problematic to design and manufacture. This is a design trade-off. Thus, increasing the extension h of the first surface area 126 and the second surface area 128 perpendicular to the first slot surface 1 12 above 2 mm will not give any useful effect on the electromagnetic coupling but will make manufacturing more difficult. When tuning a multimode radio frequency resonator 100 according to the embodiment shown in Figs. 1-4 a non-conductive elongated slot 106, 134, 164 is formed for each mode that is to be tuned. The amount of tuning depends on the length of the non-conductive elongated slot 106, 134, 164. Thus, the longer the non-conductive elongated slot 106, 134, 164, is made the more tuning is achieved. For tuning of the first mode the first non-conductive elongated slot 106 is formed. In the following the first slot 106 will be used as an example on how to tune the first mode of the radio frequency resonator 100. The following explanations also apply for the second non-conductive elongated slot 134 for tuning the second mode and the third non- conductive elongated 164 for tuning the third mode. The ratio between the first length 108 of the first non-conductive elongated slot 106 and the first width 1 10 of the first non-conductive elongated slot 106 is at least 2, preferably at least 5, and most preferred at least 10. The preferred first length 108 will depend on the frequency required. The first length 108 needs always to be longer than the first width 1 10 to effect a change, but does not necessarily have an upper limit other than when the desired frequency is reached or when the first length 108 is equal to the extension of the multimode radio frequency resonator 100. The first length 108 of the first non-conductive elongated slot 106 is ultimately limited by the dimensions of the multimode radio frequency resonator 100.

In case it is not possible to achieve the necessary frequency tuning even with a single slot having essentially the same length as the multimode radio frequency resonator 100 it is possible to use a plurality of parallel slots as is shown in Fig. 5, which is a perspective view of a multimode radio frequency resonator 100 according to another embodiment. The multimode radio frequency resonator 100 in Fig. 5 comprises a first ridge 130, a second ridge 132, and a third ridge 192 on the first main surface 1 14. A first non-conductive elongated slot 106 is arranged between the first ridge 130 and the second ridge 132. A second non-conductive elongated slot 194 is arranged between the second ridge 132 and the third ridge 192. The first non-conductive elongated slot 106 and the second non-conductive elongated slot 194 are oriented with their length parallel to the magnetic field lines M1 of the first mode. The first ridge 130, the second ridge 132 and the third ridge 192 constitute a first group of ridges. Similar groups of ridges 196, 198, are arranged on the second main surface 1 16 and the third main surface 1 18, respectively. The slots between the ridges are not shown on the second main surface 1 16 and the third main surface 1 18. Such slots are formed in case it is desirable to tune also the second mode and the third mode.

Fig. 6 is a perspective view of a multimode radio frequency resonator according to another embodiment. A first ridge 200 is formed on the first main surface 1 14 and a similar second ridge 202 is formed on the second main surface 1 16. Two parallel ridges 166, 168, are formed on the third main surface 118. The two parallel ridges 166, 168 formed on the third main surface 1 18 have the same shape as has been explained above with reference to Figs. 1-4 above. Slots are only shown on the second main surface 1 16. A first slot 204 and a second slot 206 are arranged on the second main surface 1 16. The second ridge 202 comprises a main ridge 208, a first sub-ridge 210, a second sub-ridge 212, and a third sub-ridge 214. The first sub- ridge 210, the second sub-ridge 212, and the third sub-ridge 214, extend perpendicular to the main ridge. The first slot 204 is arranged with its length along the main ridge 208 and between the first sub-ridge 210 and the second sub-ridge 212. The second slot 206 is arranged with its length along the main ridge 208 and between the second sub-ridge 212 and the third sub-ridge 214. The multimode radio frequency resonator 100 in Fig. 6 may be manufactured with die- pressing along one axis, namely perpendicular to the third main surface 1 18. The lack of a ridge on the opposing the main ridge 208 is compensated for by the first sub-ridge 210, the second sub-ridge 212, and the third sub-ridge 214. Fig. 7 is a perspective view of a multimode radio frequency resonator 100 according to another embodiment. On the first main surface 1 14 a first ridge 130 and a second ridge 132 are arranged parallel to each other as has been described with reference to Figs. 1-4. On the second main surface 1 16 pairs of curved ridges 216 are arranged. No non-conductive elongated slots are shown in Fig. 7. However, such non-conductive elongated slots are to be formed between the first ridge 130 and the second ridge 132 and between the pairs of curved ridges 216. The pairs of curved ridges 216 on the second main surface 1 16 are adapted for tuning of the third mode. The magnetic field M3 of the third mode is circular at the second main surface 1 16.

Fig. 8 is a perspective view of a multimode radio frequency resonator 100 according to another embodiment. The only difference between the embodiment shown in Fig. 7 and the embodiment shown in Fig. 8 is that a third ridge 160 and a fourth ridge 162, as was described with reference to Fig. 3, are arranged on the second main surface 1 16. No non-conductive elongated slots are shown in Fig. 8. However, such non-conductive elongated slots are to be formed between the first ridge 130 and the second ridge 132, between the third ridge 160 and the fourth ridge 162 and between the pairs of curved ridges 216. The third ridge 160 and the fourth ridge 162 are adapted for tuning of the second mode as the magnetic field M2 of the second mode is parallel to the third ridge 160 and the fourth ridge 162.

Common to the embodiments shown in Fig. 7 and Fig. 8, is that they can be formed by die- pressing along one axis, namely perpendicular to the second main surface 1 16.

Figs. 9-12 are perspective views of further multimode radio frequency resonators 100 according to different embodiments. In contrast to the embodiments described above the multimode radio frequency resonators 100 shown in Figs. 9-12 comprise no ridges. Instead trenches are formed in the first main surface 1 14, the second main surface 1 16 and the third main surface 1 18. Thus, in Fig. 9 a first trench 218 is formed in the first main surface 1 14, a second trench 220 is formed in the second main surface 1 16, and a third trench 222 is formed in the third main surface 1 18. In Fig. 10 the first trench 218, the second trench 220, and the third trench 222 extend along the entire length of the multimode radio frequency resonator 100. In Fig. 9 the first trench 218, the second trench 220, and the third trench 222 extend along only a part of the length of the multimode radio frequency resonator 100. The third trench 222 has a first sidewall 152 and a second sidewall 154. A fifth surface area 178, facing the third non- conductive elongated slot 164 covered by the conductive layer 104, is arranged on the first sidewall 152 of the third trench 222 and a sixth surface area 180, facing the third non- conductive elongated slot 164 covered by the conductive layer 104, is arranged on the second sidewall 154 of the third trench 222. The fifth surface area 178 and the sixth surface area 180 are perpendicular to the third non-conductive elongated slot 164.

In Fig. 1 1 the trenches are doubled so that two first trenches 218 are formed in the first main surface 1 14, two second trenches 220 are formed in the second main surface 1 16, and two third trenches 222 are arranged on the third main surface. As has been described above this increases the tuning range of the multimode radio frequency resonator 100. The difference between the embodiment shown in Fig. 1 1 and the embodiment shown in Fig. 12 is that only one third trench 222 is shown which and has been moved from the third main surface 1 18 to the first main surface 1 14. Thus, the third trench 222 crosses the two first trenches 218. It is shown in Fig. 12 that the number of slots used can be chosen arbitrarily, as required by the design. Any combination of self-shielding features may be chosen and utilised as required by the design.

Fig. 13 shows in a side view the multimode radio frequency resonator 100 of Fig. 10. As can be seen in Fig. 13 most of the electric field lines 230 from the first non-conductive emitted from the elongated slot 106 are self-shielded by the first surface area 126 and the second surface area 128.

Fig. 14 shows the resonance frequency (in MHz) for the first mode as a function of the first length 108 of the first non-conductive elongated slot 106 (in mm) in a multimode radio frequency resonator as shown in Fig. 1 when the resonance frequency of the second and third mode are equal. In Fig. 14 the first mode is called mode X, the second mode is called mode Y and the third mode is called mode Z. As can be seen in Fig. 14 the resonance frequency of the first mode is slightly above the resonance frequencies for the second mode and the third mode when the first length 108 of the first non-conductive elongated slot 106 is short. When the first length 108 of the first non-conductive elongated slot 106 passes 5 millimetres the resonance frequency of the first mode becomes lower than the resonance frequencies for the second mode and the third mode. The resonance frequencies for the second mode and the third mode are essentially unaffected by the first length 108 of the first non-conductive elongated slot 106.

Fig. 15 shows the resonance frequency (in MHz) for the first mode as a function of the first length 108 of the first non-conductive elongated slot 106 in a multimode radio frequency resonator as shown in Fig. 1 when the resonance frequency of the second mode differ from the resonance frequency of the third mode. Also in this figure it is seen that the resonance frequency of the first mode changes when the first length 108 of the first non-conductive elongated slot 106 is increased while the resonance frequencies for the second mode and the third mode are essentially unaffected.

Fig. 16 shows an assembly with a first multimode radio frequency resonator 100 and a second multimode radio frequency resonator 100 ' according to the embodiment in Fig. 5, in close proximity to an external cover 228. The second main surface 1 16 of the first multimode radio frequency resonator 100 and the second main surface 1 16 ' of the second multimode radio frequency resonator 100 ' each comprise a group of ridges 196, 196 ' . Similarly, the third main surface 1 18 of the first multimode radio frequency resonator 100 and the third main surface 1 18 ' of the second multimode radio frequency resonator 100 ' each comprise a group of ridges 198, 198 ' . Non-conductive elongated slots (not shown in Fig. 16) are arranged between the ridges 196, 196 ' , 198, 198 ' . Due to the self-shielding properties only a very small amount of the electric field will be emitted from the groups of ridges 196, 198. It is only the electromagnetic field that is emitted from the groups of ridges that can interact with the external cover 228 or with the groups of ridges 196, 198, ' 196 ' , 198 ' , on the adjacent multimode radio frequency resonator 100. The electromagnetic field that is emitted from the groups of ridges 196, 198, 196 ' , 198, is very small due to the self-shielding described. Thus, the distance between the multimode radio frequency resonator 100, 100 ' , and the external cover does not have any essential influence on the resonance frequency of the multimode radio frequency resonator 100, 100 ' . In the absence of self-shielding features, such as the ridges 130, 132, 160, 162, 166, 168, described the emanating fields from any removed conductive coating 104, for tuning or otherwise, would interact with the external cover 228 and other separate components. As such, the use of the described embodiments is most beneficial when it is combined in such closely packed assemblies as found, for example, behind an array of antennas or similar.

Fig. 17 shows the power radiated, normalized relative to slot with no ridges, from a slot in Fig. 1 as a function of the distance between the first surface area 126 and the second surface area 128 for different extensions h of the first surface area 126 and the second surface area 128 perpendicular to the first slot surface 112. The extension h is called ridge H in Fig. 17

Fig. 18 shows the change in resonant frequency in percent of a multimode radio frequency resonator 100 according to Fig. 1 as a function of the distance for the slot surface 1 12 to the external cover 228 for different extensions h of the first surface area 126 and the second surface area 128 perpendicular to the first slot surface 1 12. The extension h is called recess depth in Fig. 18. Fig. 19 shows schematically a communication device 300 in a wireless communication system 400. The communication device 300 comprises a multimode radio frequency resonator 100 according to an embodiment of the invention. The wireless communication system 400 also comprises a base station 500 which may also comprise a multimode radio frequency resonator 100 according to any one of the embodiments described above. The dotted arrow A1 represents transmissions from the transmitter device 300 to the base station 500, which are usually called up-link transmissions. The full arrow A2 represents transmissions from the base station 500 to the transmitter device 300, which are usually called down-link transmissions. The present transmitter device 300 may be any of a User Equipment (UE) in Long Term Evolution (LTE), mobile station (MS), wireless terminal or mobile terminal which is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UE may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).

The present transmitter device 300 may also be a base station a (radio) network node or an access node or an access point or a base station, e.g., a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network nodes may be of different classes such as, e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).