WO2021213630A1

WO2021213630A1 - A resonant device comprising resonant elements within a resonant cavity

Info

Publication number: WO2021213630A1
Application number: PCT/EP2020/061067
Authority: WO
Inventors: Senad Bulja; Pawel Rulikowski; Florian Pivit
Original assignee: Nokia Technologies Oy
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-10-28

Abstract

A resonant device comprising at least: a first resonant cavity comprising one or more first resonant elements extending parallel to a first direction; a second resonant cavity comprising one or more second resonant elements extending parallel to the first direction, wherein the first and second resonant cavities are adjacent and relatively displaced parallel to the first direction; and coupling means for electromagnetically coupling the first resonant cavity and the second resonant cavity.

Description

TITLE

A resonant device comprising resonant elements within a resonant cavity.

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate to a resonant device comprising resonant elements within a resonant cavity.

BACKGROUND

A resonant device is a component that has a frequency selective impedance as a consequence of resonant modes supported by the resonant device.

The arrangement of resonant elements within a resonant cavity of a resonant device varies a distributed capacitance and inductance and, as a consequence, varies the resonant modes of the resonant device.

It can for example be desirable for a resonant device to have a high transmission coefficient at passband frequencies and to have a low transmission coefficient for stopband frequencies.

It can for example be desirable for a resonant device to be compact (small volume).

It can for example be desirable for a resonant device to be usable in high power applications.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments there is provided a resonant device comprising at least: a first resonant cavity comprising one or more first resonant elements extending parallel to a first direction; a second resonant cavity comprising one or more second resonant elements extending parallel to the first direction wherein the first and second resonant cavities are adjacent and relatively displaced parallel to the first direction; and coupling means for electromagnetically coupling the first resonant cavity and the second resonant cavity. In at least some but not necessarily all examples, the coupling means comprises a through-aperture between the first resonant cavity and the second resonant cavity.

In at least some but not necessarily all examples, the through-aperture extends through a conductive wall that is shared by the first resonant cavity and the second resonant cavity.

In at least some but not necessarily all examples, at least one of the first resonant elements extends in the first direction from a first wall of the first resonant cavity, at least one of the first resonant elements extends in a direction opposite to the first direction from a second wall of the first resonant cavity, opposite the first wall of the first resonant cavity; and wherein at least one of the second resonant elements extends in the first direction from a first wall of the second resonant cavity, and at least one of the second resonant elements extends in a direction opposite to the first direction from a second wall of the second resonant cavity, opposite the first wall of the second resonant cavity.

In at least some but not necessarily all examples, each of the first resonant elements that extend in the first direction from the first wall of the first resonant cavity has, as a nearest neighbor, a first resonant element that extends in the direction opposite to the first direction from the second wall of the first resonant cavity and each of the first resonant elements that extends in the direction opposite to the first direction from the second wall of the first resonant cavity has, as a nearest neighbor, a first resonant element that extends in the first direction from the first wall of the first resonant cavity; and each of the second resonant elements that extends in the first direction from the first wall of the second resonant cavity has, as a nearest neighbor, a second resonant element that extends in the direction opposite the first direction from the second wall of the second resonant cavity, and each of the second resonant elements that extends in the direction opposite to the first direction from the second wall of the second resonant cavity has, as a nearest neighbor, a second resonant element that extends in the first direction from the first wall of the second resonant cavity.

In at least some but not necessarily all examples, the first resonant elements are arranged as a matrix comprising rows and columns, wherein the first resonant elements that extend in the first direction from the first wall of the first resonant cavity and the first resonant elements that extend in the direction opposite the first direction from the second wall of the first resonant cavity alternate in the rows and in the columns and/or wherein the second resonant elements are arranged as a matrix comprising rows and columns, wherein the second resonant elements that extend in the first direction from the first wall of the second resonant cavity and the second resonant elements that extend in the direction opposite the first direction from the second wall of the second resonant cavity alternate in the rows and in the columns.

In at least some but not necessarily all examples, the first resonant cavity comprises more than twenty first resonant elements extending parallel to the first direction and/or wherein the second resonant cavity comprises more than twenty second resonant elements extending parallel to the first direction.

In at least some but not necessarily all examples, the first resonant elements are freestanding posts and/or wherein the second resonant elements are freestanding posts.

In at least some but not necessarily all examples, the apparatus is configured to operate as a filter.

In at least some but not necessarily all examples, the filter has a center frequency of a bandpass, wherein a length of the first resonant elements and a length of the second resonant elements in the first direction are less than one eighth of a wavelength equivalent to the center frequency or a length of the first resonant elements and a length of the second resonant elements in the first direction are less than one twentieth of the wavelength equivalent to the center frequency.

In at least some but not necessarily all examples, the first resonant cavity is a substantially closed first conductive enclosure and the second resonant cavity is a substantially closed second conductive enclosure, and wherein the coupling means provides an aperture between the first and second enclosures, wherein the first enclosure and the second enclosure share a common intervening wall.

In at least some but not necessarily all examples, the first resonant cavity and the second resonant cavity are defined within a printed circuit board. In at least some but not necessarily all examples, the resonant device is comprised in radio frequency circuitry.

In at least some but not necessarily all examples, the resonant device is comprised in an electronic component.

In at least some but not necessarily all examples, the resonant device is comprised in a cellular base station configured for massive multiple input multiple output (mMIMO).

According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

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

FIG. 1 shows an example of the subject matter described herein;

FIG. 2A shows another example of the subject matter described herein;

FIG. 2B shows another example of the subject matter described herein;

FIG. 3A & 3B show another example of the subject matter described herein;

FIG. 4A & 4B show another example of the subject matter described herein;

FIG. 5A shows another example of the subject matter described herein;

FIG. 5B shows another example of the subject matter described herein;

FIG. 6 shows another example of the subject matter described herein;

FIG. 7 shows another example of the subject matter described herein;

FIG. 8 shows another example of the subject matter described herein;

FIG. 9A and FIG 9B show another example of the subject matter described herein; FIG. lOA and FIG 10B show another example of the subject matter described herein.

DETAILED DESCRIPTION

In the following description different features are referred to using different reference numerals and similar features are referred to using similar reference numerals. For example, a resonant device 10 comprises resonant cavities 20 that comprise resonant elements 22 that depend from opposite walls 24, 26. A feature associated with a particular resonant cavity 20_n will be identified using a first subscript index n. For example, resonant cavity 20_n comprises one or more resonant elements 22_n that extend parallel to a first direction 11. A second index m may be used to distinguish resonant elements 22_nm that extend parallel to the first direction 11 but in different senses. For example, the resonant elements 22_ni , extend in the first direction 11 from the wall 24_n of the resonant cavity 20_n and resonant elements 22_n2, extend in a direction opposite to the first direction 11 from the opposite wall 26_n of the resonant cavity 20_n.

The following figures illustrate various examples of a resonant device 10 comprising at least a first resonant cavity 20i and a second resonant cavity 2O₂. The resonant device 10 comprises coupling means 12 for electromagnetically coupling the first resonator cavity 20i and the second resonant cavity 2O₂. The first resonant cavity 20i comprises one or more first resonant elements 22n, 22i₂ that extend parallel to a first direction 11. The second resonant cavity 2O₂ comprises one or more second resonant elements 22₂₁, 22₂₂ that extend parallel to the first direction 11. The first and second resonant cavities 20I_,20₂ are adjacent and relatively displaced parallel to the first direction 11.

The stacking of the first resonant cavity 20i adjacent to the second resonant cavity 2O₂ with the provision of coupling means 12 between them provides fora compact resonant device 10. The resonant device 10 operates as a coupled resonator system.

The resonant elements 22 within a resonant cavity 20 are closely coupled, distributed resonant elements. In at least some of the examples, the resonant elements 22 are alternating in that they alternately depend from opposing walls 24, 26 of the respective resonant cavity 20.

In the example of FIG. 1, the first resonant cavity 20i comprises multiple first resonant elements 22i that extend parallel to the first direction 11 within the first resonant cavity 20i. Some of the first resonant elements 22i, the first resonant elements 22n, extend in the first direction 11 from a first wall 24i of the first resonant cavity 20i. Some of the first resonant elements 22i, the first resonant elements 22i₂, extend in a direction opposite to the first direction 11 from a second wall 26i of the first resonant cavity 20i, opposite the first wall 24i of the first resonant cavity 20i.

The second resonant cavity 2O₂ comprises multiple second resonant elements 22₂ that extend parallel to the first direction 11 within the second resonant cavity 2O₂. Some of the second resonant elements 22₂, the second resonant elements 22₂₁, extend in the first direction 11 from a first wall 24₂ of the second resonant cavity 2O₂. Some of the second resonant elements 22₂, the second resonant elements 22zi, extend in a direction opposite to the first direction 11 from a second wall 26₂ of the second resonant cavity 2O₂, opposite the first wall 24₂ of the second resonant cavity 2O₂.

In the example illustrated there are two resonant cavities 20i, 2O₂. However, in other examples there may be more resonant cavities 20. An arbitrary one of the resonant cavities 20, the nth resonant cavity 20_n comprises multiple resonant elements 22_n extending parallel to the first direction 11 and it also comprises coupling means 12 for electromagnetically coupling the nth resonant cavity 20_n to another resonant cavity (for example adjacent resonant cavity 20_n+i and/or adjacent resonant cavity 20_n-i). The nth resonant cavity 22_n has a first wall 24_n and an opposing second wall 26_n. The resonant elements 22_n include multiple resonant elements 22_ni that extend in the first direction 11 and multiple resonant elements 22_n2 that extend in the direction opposite to the first direction 11. The resonant elements 22_ni extend in the first direction 11 from the first wall 24_n and the resonant elements 22_n2 extend in the opposite direction from the second wall 26_n.

In the example illustrated in FIG. 1, a particular number of stacked resonant cavities 20_n is illustrated. It should of course be realized that a resonant device 10 can comprise more resonant cavities 20 stacked in the first direction and intercoupled by coupling means 12. In some examples, the coupling means 12 comprises only direct couplers that couple directly adjacent resonant cavities 20 in the stack. In some examples, the coupling means 12 can comprises cross-couplers that couple non- adjacent resonant cavities 20 in the stack.

In the example illustrated in FIG. 1, a particular number of resonant elements 22 is illustrated in each resonant cavity 20. It should of course be realized that a resonant cavity 20 can comprise one or more resonant elements 22. For example, there may be two, three or many more resonant elements 22_n.

The resonant elements 22 are freestanding posts. The term post is used to indicate that the resonant element extends from one side towards another side but does not reach the other side but instead ends at a terminus. A post is therefore to be differentiated from a pillar that would extend across from one side of the resonant cavity 20 to the other side of the resonant cavity 20. For example, the resonant elements 22_ni extend in the first direction 11 from the first wall 24_n of the resonant cavity 20_n but do not reach the second wall 26_n of the resonant cavity 20_n. The resonant elements 22_n2 extend in the opposite direction to the first direction 11 from the second wall 26_n of the resonant cavity 20_n but do not reach the first wall 24_n of the resonant cavity 20_n.

There are therefore gaps, in the first direction 11 , between the terminus of resonant element 22_ni and the second wall 26_n of the resonant cavity 20_n. There are also gaps, in the first direction 11, between the terminus of the resonant elements 22_n2 and the first wall 24_n of the resonant cavity 20_n. There are also lateral gaps, in planes orthogonal to the first direction 11 , between any one of the resonant elements 22 and any other of the first resonant elements 22.

The posts forming the resonant elements 22 can each have a non-constant cross- section. For example, they may have a cross-sectional area that increases towards their terminus. This can, for example, form a larger area cap to increase capacitance. For example, they may have a cross-sectional area that decreases towards their terminus, for example, if resonant elements are made using metal drawing fabrication techniques.

In the example illustrated in FIG. 1 , each of the resonant elements 22 is a post of the same dimension. They have the same shape, same length and the same cross- sectional area. However, this is not necessary. In some examples the resonant elements 22 may vary in shape and/or length and/or cross-sectional area.

The posts that form the resonant elements 22 can be formed from conductive material such as aluminum, copper, brass. In some examples they may be formed from milled or molded metal or other conductive material. In other examples the conductive material may be a plated material such as for example silver or gold.

As can be seen from FIG. 1, and FIGS 2A and 2B, each of the first resonant elements 22ii that extend in the first direction 11 from the first wall 24i of the first resonant cavity 20i has, as a nearest neighbor or nearest neighbors, a first resonant element 22i₂ that extends in the direction opposite to the first direction 11 from the second wall 26i of the first resonant cavity 20i. Also each of the first resonant elements 22i₂ that extends in the direction opposite to the first direction 11 from the second wall 26i of the first resonant cavity 20i has, as a nearest neighbor or nearest neighbors, a first resonant element 22n that extends in the first direction 11 from the first wall 24i of the first resonant cavity 20i.

Each of the second resonant elements 22_2i that extend in the first direction 11 from the first wall 24₂ of the second resonant cavity 2O₂ has, as a nearest neighbor or nearest neighbors, a second resonant element 22zi that extends in the direction opposite the first direction 11 from the second wall 26₂ of the second resonant cavity 2O₂. Each of the second resonant elements 22zi that extend in the direction opposite to the first direction 11 from the second wall 26₂ of the second resonant cavity 2O₂ has, as a nearest neighbor or nearest neighbors, a second resonant element 22₂₁ that extends in the first direction 11 from the first wall 24₂ of the second resonant cavity 2O₂.

As can be seen in FIG. 2B and at least some examples, the resonant elements 22_n are arranged as a two-dimensional rectangular matrix comprising rows (horizontal in the page) and columns (vertical in the page). The nth resonant elements 22_ni that extend in the first direction 11 from the first wall 24_n of the nth resonant cavity 20_n and the nth resonant elements 22_n2 that extend in the direction opposite the first direction 11 from the second wall 26_n of the nth resonant cavity 20_n alternate in the rows and alternate in the columns. Each resonant element 22_ni that extend in the first direction 11 from the first wall 24_n of the nth resonant cavity 20_n has as nearest neighbors in the horizontal and vertical directions only the resonant elements 22_n2 that extend in the direction opposite the first direction 11 from the second wall 26_n of the resonant cavity 20_n. Each resonant element 22_n2 that extends in the direction opposite the first direction 11 from the second wall 26_n of the resonant cavity 20_n has as nearest neighbors in the horizontal and vertical directions only the resonant elements 22_ni that extend in the first direction 11 from the first wall 24_n of the nth resonant cavity 20_n

The resonant elements 22_ni are aligned only along diagonal lines 21 _ni . The resonant elements 22_n2 are aligned only along diagonal lines 21 m.

The alternating arrangement of the differently oriented resonant elements 22_ni, 22_n2 within a resonant cavity 20_n generates strong magnetic coupling in the lateral gaps between the differently oriented resonant elements 22_ni , 22m- In some examples, the resonant cavities 20_n can comprise a large number of resonant elements 22_n. For example, some, one or all of the resonant cavities 20 can comprise more than 20 resonant elements 22 extending parallel to the first direction 11. In some examples, the number of resonant elements 22 within a resonant cavity 20 can be even higher, for example it may be greater than 100. For example, the resonant elements 22 could, for example, be arranged as an 11 column by 11 row matrix. The large number of resonant elements 22 results in the resonant device 10 being less susceptible to the effect of random variations in the shape of the resonant elements 22 that could arise for manufacturing tolerance because of regression to the mean. As a consequence, the characteristics of the resonant device 10 can, in at least some examples, be accurately controlled. This may allow the resonant device 10 to have less or no tuning elements, such as tuning screws.

The large number of resonant elements 22 extending parallel to the first direction 11 distributes the capacitance and inductance of the resonant device 10. This allows resonant elements 22 of shorter extent (length) parallel to the first direction to be used. This creates a resonant device 10 of less height in the first direction 11.

For example, a length of the resonant elements 22 in the first direction 11 can be less than one eighth, one twentieth or one thirtieth of a wavelength equivalent to a resonant frequency of the resonant device 10. This allows each resonator cavity 20 to have a reduced dimension in the first direction, and allows the resonant device 10 to be compact with a reduced height in the first direction 11 even with multiple resonator cavities 20 stacked in the first direction 11.

Thus, despite the large number of resonant elements, it is still possible to maintain a compact size for the resonant device 10. For example, the size of the resonant device 10 can, in some examples, be as small as 3mm x 4mm x 0.2mm. In this example, the resonant device 10 has a height 0.2mm in the first direction 11.

In at least some examples, the resonant elements 22_ni, which extend in the first direction 11 from the wall 24_n of the resonant cavity 20_n, are formed from tabs formed in a first planar conductive sheet that are each bent from a base at the first planar conductive sheet at right angles to the plane of the first planar conductive sheet. The tabs can be formed by stamping and deforming the first planar conductive sheet. For example, stamping a U-shaped cut-out creates a U-shaped tab. The resonant elements 22_ni can be formed using a tool that in a single linear motion cuts the first planar conductive sheet to form the tabs and then bends the tabs. The first stamped planar conductive sheet can be joined to a parallel first unstamped planar conductive sheet to form the wall 24_n of the resonant cavity 20_n.

The resonant elements 22_n2, which extend in a direction opposite to the first direction 11 from the wall 26_n of the resonant cavity 20_n, are formed from tabs formed in a second planar conductive sheet that are each bent from a base at the second planar conductive sheet at right angles to the plane of the second planar conductive sheet. The tabs can be formed by stamping and deforming the second planar conductive sheet. For example, stamping a U-shaped cut-out creates a U-shaped tab. The resonant elements 22_n2 can be formed using a tool that in a single linear motion cuts the second planar conductive sheet to form the tabs and then bends the tabs. The second stamped planar conductive sheet can be joined to a parallel second unstamped planar conductive sheet to form the wall 26_n of the resonant cavity 20_n

Where resonant cavities 20_n are stacked, a single planar conductive sheet can be used as the first unstamped planar conductive sheet of one cavity and the second unstamped planar conductive sheet of a directly adjacent cavity.

A tab is a planar elongate element that also has breadth and is attached at only one end length-wise and at neither end breadth-wise.

The bent tabs are freestanding posts. The length of a tab is less than the separation distance between the stamped planar conductive sheets of a resonant cavity 20_n. There are therefore gaps, in the first direction 11 , between the terminus of resonant element 22_ni and the second wall 26_n of the resonant cavity 20_n. There are also gaps, in the first direction 11, between the terminus of the resonant elements 22_n2 and the first wall 24_n of the resonant cavity 20_n. The tabs can be posts of the same dimension. They can have the same shape, same length and the same cross-sectional area. However, this is not necessary.

FIGS 3A and 3B illustrate another example of a resonant device 10 as previously described. FIG. 3A illustrates a cross-sectional view through the resonant device 10. FIG. 3B illustrates the same resonant device 10 as illustrated in FIG. 3A except that an upper wall 35 of the resonant device 10 has been removed to more clearly illustrate the arrangement of resonant elements 22. In the following the terms ‘upper’ and ‘lower’ are used with reference to the FIGs and not necessarily the resonant device 10 when in use.

The first resonant cavity 20i is a substantially closed first conductive enclosure and the second resonant cavity 2O₂ is a substantially closed second conductive enclosure. The coupling means 12 provides an aperture 40 between the first and second enclosures. In this example, the first enclosure and the second enclosure share a common intervening wall 37. The first resonant cavity 20i is substantially closed in that it is closed except for openings for input, output or for coupling to another cavity. The second resonant cavity is substantially closed in that it is almost entirely closed except for openings for input, output or for coupling to another resonant cavity 20.

In this example, a conductive housing 30 of the resonant device 10 comprises an upper conductive wall 31 and a lower conductive wall 32 and also comprises a first pair of opposing side walls 33, 34 and a second pair of opposing side walls 35, 36. The side wall 36 is not illustrated as it has been cut away in the cross-section. The housing 30 is a substantially cuboid shape. An intermediate wall 37 extends parallel to the upper and lower walls 31, 32 and divides the housing into the first resonant cavity 20i and the second resonant cavity 2O₂. The first wall 24i of the first resonant cavity 20i is provided by the upper wall 31 of the housing and the second wall 26i of the first resonant cavity 20i is provided by the intermediate wall 37. The first wall 24₂ of the second resonant cavity 2O₂ is provided by the intermediate wall 37 and the second wall 26₂ of the second resonant cavity 2O₂ is provided by the lower wall 32. An aperture 40 in the intermediate wall 37 provides the coupling means 12 between the first resonant cavity 20i and the second resonant cavity 2O₂. The coupling means is a through- aperture between the first resonant cavity 20i and the second resonant cavity 2O₂, and, in this particular example, is a through-aperture 40 that extends through a conductive wall 37 that is shared by the first resonant cavity 20i and the second resonant cavity 2O2.

In this example, the size of the aperture 40 has a cross-sectional area that is of a similar size to a cross-sectional area of a resonant element 22. The cross section of the aperture 40 can be of almost any shape - can be square, triangular, rectangular or circular. Furthermore, one can have more than one aperture 40 for inter-resonant cavity coupling. For great filter bandwidth a great deal of coupling between resonator elements is required, which necessitates bigger apertures 40. If one aperture is not enough, multiple apertures 40 can be used, for example apertures 40 can be placed adjacent some or all of the four side walls of a resonator cavity 20 that requires inter cavity coupling.

The resonant device 10 comprises two input/output ports 50. In this particular example, but not necessarily all examples, the upper wall 31 of the resonant device 10 comprises an input/output port 50 and the lower wall 32 of the resonant device 10 comprises an output/input port 50. The resonant device 10 is a two-port device that has a selective reflection/transmission coefficient for particular frequencies.

In the example illustrated, the space within the resonant cavities 20i, 2O2 that is not occupied by the resonant elements 22 comprises air, which operates as a dielectric. In other examples, the space may be filled by a dielectric material, or in some examples filled with a combination of two or more dielectric materials, one of which could be air. In some examples, at least one dielectric material could be a composite dielectric material comprising two or more different dielectric materials/air.

In this example, there is no aperture in the housing 30 for a tuning element such as a tuning screw for any of the resonant cavities 20. However, in other examples, an aperture may be provided for one or more tuning elements, for example tuning screws.

The resonant device 10 can, for example, have a quality (Q) factor greater than 1000.

The stacked resonant cavities can comprise resonant elements 22_n that are aligned in the first direction 11. For example, the pattern of the resonant elements 22_n in a nth resonant cavity 20_n can be the same as and be aligned with the pattern of resonant elements 22_m in any of the other resonant cavities 20_m that are stacked, in the first direction, with the resonant cavity 20_n.

FIGS 4A and 4B illustrate another example of a resonant device 10 as previously described. FIG. 4A illustrates a cross-sectional view through the resonant device 10. FIG. 4B illustrates the same resonant device 10 as illustrated in FIG. 4A except that an upper wall 31 of the resonant device 10 has been removed to more clearly illustrate the arrangement of resonant elements 22. In the following the terms ‘upper’ and ‘lower’ are used with reference to the FIGs and not necessarily the resonant device 10 when in use.

The resonant device 10 in FIGs 4A, 4B is similar to the resonant device 10 illustrated in FIG 3A, 3B. It, however, has a greater number of resonant cavities 20, stacked parallel to the first direction 11. Resonant cavities 20_n, 20_n+i that are adjacently stacked are separated by an intermediate wall 37. An aperture 40 in each intermediate wall 37 provides a coupling means 12 (direct-coupler 12_d) between the adjacent resonant cavities 20_n, 20_n+i. The apertures 40 are through-apertures between the cavities 20_n, 20_n+i and extend through the conductive wall 37 that is shared by the adjacent resonant cavities 20_n, 20_{n+i .} The resonant device 10 also comprises coupling means 12 between non-adjacent cavities 20_n, 20_n+P (p>1). An interconnecting sealed conduit provides an aperture 40 between the non-adjacent cavities 20_n, 20_n+P that are separated by (p-1) intermediate resonant cavities 20 and by p intermediate walls 37. The interconnecting sealed conduit passes through the (p-1) intermediate resonant cavities 20 and the p intermediate walls 37.

In this example, the size of the apertures 40 have a cross-sectional area that is of a similar size to a cross-sectional area of a resonant element 22.

Each resonant cavity 20 can be a substantially closed conductive enclosure with one or more coupling means 12 to one or more other resonant cavities 20. Each enclosure shares a common intervening wall 37 with each adjacent resonant cavity 20 in the stack. The resonant cavity 20 is substantially closed in that it is closed except for openings for input, output or for coupling to another resonant cavity 20 or resonant cavities 20.

A conductive housing 30 of the resonant device 10 comprises an upper conductive wall 31 and a lower conductive wall 32 and also comprises a first pair of opposing side walls 34, 33 (not labelled) and a second pair of opposing side walls 35, 36 (not labelled). The orientation of the conductive walls 31, 32, 34 (labelled) and 33, 35, 36 (not labelled) is as illustrated previously in FIG 3A. The side wall 36 is not illustrated as it has been cut away in the cross-section. The housing 30 is a substantially cuboid shape. Intermediate walls 37 extend parallel to the upper and lower walls 35, 36 and divide the housing 30 into the multiple resonant cavities 20 that are stacked parallel to the first direction 11. The first wall 24i of the first resonant cavity 20i is provided by the upper wall 31 of the housing and the second wall 26₂ of the last/lowest resonant cavity 2O₄ is provided by the lower wall 32.

In the example illustrated, the space within the resonant cavities 20i, 2O₂ that is not occupied by the resonant elements 22 comprises air, which operates as a dielectric. In other examples, the space may be filled by a dielectric material or in some examples filled with a combination of two or more dielectric materials, one of which could be air. In some examples, at least one dielectric material could be a composite dielectric material comprising two or more different dielectric materials/air.

FIGS 5A and 5B illustrate different arrangements of resonant elements 22_ni , 22_n2 within a resonant cavity 20_n. In these examples it can be seen that the resonant elements 22_ni that extend in the first direction 11 from an (upper) wall of the cavity are aligned along parallel lines 21 _ni and that the resonant elements 22_n2 that extend in the opposite direction to the first direction 11 from a (lower) wall of the resonant cavity 20_n are aligned along lines 21 „ All the resonant elements 22_ni (or all the resonant elements 22_ni along a line 21 _ni) can have the same shape, the same length parallel to the first direction 11, the same cross-sectional area orthogonal to the first direction 11 , or in other examples can have differing shapes, lengths or cross-sectional areas. Likewise, all the resonant elements 22_ni (or all the resonant elements 22_ni along a line 21 _n2) can have the same shape, the same length parallel to the first direction 11, the same cross- sectional area orthogonal to the first direction 11, or in other examples can have differing shapes, lengths or cross-sectional areas.

In the example of FIG. 5A, the resonant elements 22 have substantially the same shape. They are cylindrical posts.

In the example of FIG. 5B, the downwardly extending resonant elements 22_ni have a differently oriented shape to the upwardly extending resonant elements 22_n2. The resonant elements 22_ni and the resonant elements 22_n2 are both posts with a substantially semicircular cross-section. However, the orientation of the semicircular cross-sectional area for the resonant elements 22_ni is opposite to that for the resonant elements 22_n2.

In at least some of the examples, the resonant device 10 is configured to operate as a bandpass filter having at least one bandpass frequency range and a center frequency of the at least one bandpass frequency range. For example, the resonant devices 10 in FIGs 3A, 3B and 4A, 4B can be used as multipole filters, where each layer in the stack provides a pole of the filter. The two-port S-parameters (S11 and S21) for the two-pole filter of FIGs 3A, 3B are illustrated in FIGs 9A and 9B. The filter has a bandpass frequency range (defined at e.g. -10dB for S11) of approximately 1.2GHz and has a center frequency of 10GHz. The two-port S-parameters (S11 and S21) for the four-pole filter of FIGs 4A, 4B are illustrated in FIGs 10A and 10B. The filter has a bandpass frequency range (defined at e.g. -10dB for S11) of approximately 1GHz and has a center frequency of 10GHz.

The maximum length of any of the resonant elements 22 parallel to the first direction 11 can, for example, be less than 1/8, 1/20 or 1/30 a wavelength equivalent to the center frequency. The maximum height of a resonant cavity of the resonant device 10 parallel to the first direction 11 can, for example, be less than 1/8, 1/20 or 1/30 a wavelength equivalent to the center frequency. FIG 6 illustrates an example of a resonant device 10 in which conductive planar layers within a multi-layer PCB 70 can be used to form the upper, intermediate and lower layers 31, 37, 32 of the resonant device 10. Through-vias (through-openings) between those layers can be filled with conductive material to form the side walls 33, 34, 35, 36. Partial vias that extend partway through a dielectric 72, from one of the conductive planar layers 31 , 37, 32 towards but not to another one of those layers 31 , 37, 32, can be filled with conductive material to form the resonant elements 22. A dielectric-filled via through an intermediate layer 37 can be used to form the coupling means 12.

FIG. 7 illustrates an example of radio frequency circuitry 100 comprising the resonant device 10 as previously described. The radio frequency circuitry can for example be or be part of radio frequency receiver circuitry that is configured to receive radio frequency electromagnetic signals via an antenna 102, radio frequency transmitter circuitry that is configured to transmit radio frequency electromagnetic signals via an antenna 102 or radio frequency transceiver circuitry that is configured to transmit/receive radio frequency electromagnetic signals via an antenna 102.

Thus, in FIG 7 a single resonant device 10 is coupled to a single antenna 102. In other examples, a single resonant device 10 is coupled to multiple antennas 102.

An apparatus comprising the radio frequency circuitry 100 can comprise other electronic circuitry for handling or controlling other electronic signals (e.g. baseband and/or data signals), controller/processor with support circuitry (memory, registers, etc), input/output devices (keyboards, touchscreens, etc). Examples of such apparatus include but are not limited to vehicles (automobiles, ships, aircraft, drones, etc), internet of things (loTO devices, home entertainment devices, domestic devices, home security devices, etc.

In some examples, an electronic component 101 can comprise the resonant device 10 or radio frequency circuitry 100. Examples of electronic components include a module, a circuit board, an electronic device, a cellular base station, mobile equipment, user equipment, telecommunications equipment, a mobile cellular base station, part of a mobile cellular base station, a sensor for example a radar system, a point-to-point radio, a linear amplifier, a radio frequency signal cancellation circuit. FIG. 8 illustrates a particular example of an application of the resonant device 10. In this example, the radio frequency circuit 100 as illustrated in FIG. 7 used within a cellular base station 110 configured for massive multiple input multiple output (mMIMO). The cellular base station 110 comprises an array of antennas 102 each of which has radio frequency circuitry 100 comprising the resonant device 10.

Thus, in FIG 8 a single resonant device 10 couple to a single antenna 102. In other examples, a single resonant device 10 couples to an array of antennas 102 configured for massive multiple input multiple output (mMIMO).

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

As used here ‘module’ refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user.

The above described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and/or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one” or by using “consisting”.

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

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

Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

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

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

The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

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

I/we claim:

Claims

1. A resonant device comprising at least: a first resonant cavity comprising one or more first resonant elements extending parallel to a first direction; a second resonant cavity comprising one or more second resonant elements extending parallel to the first direction wherein the first and second resonant cavities are adjacent and relatively displaced parallel to the first direction; and coupling means for electromagnetically coupling the first resonant cavity and the second resonant cavity.

2. A resonant device as claimed in claim 1 , wherein the coupling means comprises a through-aperture between the first resonant cavity and the second resonant cavity.

3. A resonant device as claimed in claim 2, wherein the through-aperture extends through a conductive wall that is shared by the first resonant cavity and the second resonant cavity.

4. A resonant device as claimed in any preceding claim, wherein at least one of the first resonant elements extends in the first direction from a first wall of the first resonant cavity, at least one of the first resonant elements extends in a direction opposite to the first direction from a second wall of the first resonant cavity, opposite the first wall of the first resonant cavity; and wherein at least one of the second resonant elements extends in the first direction from a first wall of the second resonant cavity, and at least one of the second resonant elements extends in a direction opposite to the first direction from a second wall of the second resonant cavity, opposite the first wall of the second resonant cavity.

5. A resonant device as claimed in claim 4, wherein each of the first resonant elements that extend in the first direction from the first wall of the first resonant cavity has, as a nearest neighbor, a first resonant element that extends in the direction opposite to the first direction from the second wall of the first resonant cavity and each of the first resonant elements that extends in the direction opposite to the first direction from the second wall of the first resonant cavity has, as a nearest neighbor, a first resonant element that extends in the first direction from the first wall of the first resonant cavity; and each of the second resonant elements that extends in the first direction from the first wall of the second resonant cavity has, as a nearest neighbor, a second resonant element that extends in the direction opposite the first direction from the second wall of the second resonant cavity, and each of the second resonant elements that extends in the direction opposite to the first direction from the second wall of the second resonant cavity has, as a nearest neighbor, a second resonant element that extends in the first direction from the first wall of the second resonant cavity.

6. A resonant device as claimed in any preceding claim, wherein the first resonant elements are arranged as a matrix comprising rows and columns, wherein the first resonant elements that extend in the first direction from the first wall of the first resonant cavity and the first resonant elements that extend in the direction opposite the first direction from the second wall of the first resonant cavity alternate in the rows and in the columns and/or wherein the second resonant elements are arranged as a matrix comprising rows and columns, wherein the second resonant elements that extend in the first direction from the first wall of the second resonant cavity and the second resonant elements that extend in the direction opposite the first direction from the second wall of the second resonant cavity alternate in the rows and in the columns.

7. A resonant device as claimed in any preceding claim, wherein the first resonant cavity comprises more than twenty first resonant elements extending parallel to the first direction and/or wherein the second resonant cavity comprises more than twenty second resonant elements extending parallel to the first direction.

8. A resonant device as claimed in any preceding claim, wherein the first resonant elements are freestanding posts and/or wherein the second resonant elements are freestanding posts.

9. A resonant device as claimed in any preceding claim, configured to operate as a filter.

10. A resonant device as claimed in claim 9, wherein the filter has a center frequency of a bandpass, wherein a length of the first resonant elements and a length of the second resonant elements in the first direction are less than one eighth of a wavelength equivalent to the center frequency or a length of the first resonant elements and a length of the second resonant elements in the first direction are less than one twentieth of the wavelength equivalent to the center frequency.

11. A resonant device as claimed in any preceding claim, wherein the first resonant cavity is a substantially closed first conductive enclosure and the second resonant cavity is a substantially closed second conductive enclosure, and wherein the coupling means provides an aperture between the first and second enclosures, wherein the first enclosure and the second enclosure share a common intervening wall.

12. A resonant device as claimed in any preceding claim, wherein the first resonant cavity and the second resonant cavity are defined within a printed circuit board.

13. Radio frequency circuitry comprising the resonant device as claimed in any preceding claim.

14. An electronic component comprising the resonant device as claimed in any one of claims 1 to 12.

15. A cellular base station configured for massive multiple input multiple output (mMIMO) comprising the resonant device as claimed in any one of claims 1 to 12.