GB2584012A

GB2584012A - Resonator apparatus and method of use thereof

Info

Publication number: GB2584012A
Application number: GB2005437.5A
Authority: GB
Inventors: Bakr Mustafa
Original assignee: Radio Design Ltd
Current assignee: Radio Design Ltd
Priority date: 2019-05-07
Filing date: 2020-04-14
Publication date: 2020-11-18
Also published as: GB201906368D0; GB202005437D0

Abstract

Resonator apparatus including a resonant cavity defined in a housing. The resonant cavity comprises resonator means, such as a dielectric rod. The resonator apparatus includes input and output coupling means provided a spaced distance apart from, and opposite, the resonator means. The input coupling means are arranged to be a spaced distance apart from the output coupling means within the resonant cavity. The resonator means is offset from the centre of the resonant cavity. The input and output couplings are an equal distance to the resonator. The input and output means can be capacitive or inductive, such as a post arranged parallel to the longitudinal axis of the resonator means or a plate which has the same curvature as the resonator means. The resonator means walls can include grooves. The resonator can be dual mode or triple mode, and the modes can be transverse electromagnetic (TEM).

Description

Resonator Apparatus and Method of Use Thereof This invention relates to multi-mode resonator apparatus and to a method of use thereof A filter apparatus is typically used in a telecommunication system to compensate for disturbances, such as interference, that may affect one or more transmission signals being sent and/or received by the telecommunication system. The filter apparatus is designed to remove unwanted components from the transmit and/or receive signals and/or enhance the desired transmit and/or receive signals.

Telecommunication systems, such as broadcast radio, television, wireless communication systems (i.e. mobile phones, Wi-Fi etc) and/or the like which transmit and/or receive signals in the medium to high frequency ranges (i.e. in the megahertz and gigahertz frequency ranges) typically use radio frequency (RI') and microwave filter assemblies in order to filter their transmit and/or receive signals. An example of conventional RF or microwave filter apparatus typically includes a conductive housing defining one or more resonant cavities therein with one or more resonators located in each cavity. A resonator is an electronic component that exhibits resonance for a narrow range of frequencies. two or more resonators within the filter are typically electromagnetically coupled together to provide the filter with a required set of performance chara.cteristics.

Resonators can be designed to operate in either a single mode, or two or more modes and are termed multi-mode resonators. Single mode resonators resonate at a single frequency or passband. Multi-mode resonators can be arranged to operate at a single frequency or passband or two or more different frequencies or passbands.

Filters using single mode resonators tend to be relatively large, with one resonator in each cavity and each resonator resonating at a single frequency. Multi-mode resonators allow a higher order filter to be provided while occupying less physical space compared to a single mode filter, thereby allowing multi-mode filters to be more compact in design. However, filters using multi-mode resonators tend to have insufficient degrees of freedom to constitute an arbitrary response. For example, it may not be possible to control the frequency of reflection zeroes and transmission zeroes simultaneously. In addition, filter apparatus using multi-mode resonators tends to lack independence with respect to the tuning elements of the filter apparatus; this is the tuning elements provide both a primary effect which is wanted, and a secondary effect which is unwanted.

Conventionally, resonators have been located centrally of a resonant cavity within the filter housing. However, such arrangements make it difficult to separate degenerate resonant modes. US9929713 discloses a method of separating degenerate resonant modes in a. relatively simple manner by offsetting the resonator position from the centre within the resonant cavity. In doing this, the distance between the resonator and the input and output couplings associated with the resonant cavity also changes compared to a centrally located resonator. For example, the resonator can be moved closer to the input coupling (Jr closer to the output coupling. this results in the distance between the input coupling and the resonator and the distance between the output coupling and the resonator being different. US9929713 only discloses capacitive coupling between the input and output coupling and the resonator.

It is an aim' of the present invention to provide alternative resonator apparatus.

It is a Further aim of the present invention to provide a method of using alternative resonator apparatus.

It is a. yet further aim of the present invention to provide filter apparatus including resonator apparatus.

It is a yet further aim of the present invention to provide a method of using filter apparatus including resonator apparatus.

According to a first aspect of the present invention there is provided resonator apparatus, said resonator apparatus including a resonant cavity defined in a housing, resonator means provided in the resonant cavity, the resonator apparatus including input coupling means provided a spaced distance apart from and opposite the resonator means, and output coupling means provided a spaced distance apart from and opposite the resonator means, the input coupling means being a. spa.ced distance from the output coupling means within the resonant cavity, the resonator means being offset from the centre of the resonant cavity, characterised in that distance of ea.ch of the input and output coupling means to the resonator means is equal or substantially equal.

Thus, according to the present invention, 'although the resonator means is offset or off-centered within the resonant cavity, the distance between the resonator means and the input and output couplings, and therefore the electromagnetic coupling between the input and output couplings and the resonator means always remains constant, substantially constant, equal or substantially equal. This allows control of the frequency and position of the transmission zeroes and also allows a higher fractional bandwidth to be realised when the resonator apparatus forms pa.rt of radio frequency filter apparatus. The control over the placement of the transmission zeroes in the present invention can be realised without any additional coupling elements being used or changing the type of the input or output coupling means. The present invention therefore provides a. much simpler and more cost effective design for producing multi-mode filter apparatus compared to the prior art.

According to the present invention, the resonator means and/or coupling means are asymmetrically located within the resonant cavity.

Preferably the input coupling means and output coupling means provide an electromagnetic coupling with the resonator means and allows an input of electromagnetic energy and an output of electromagnetic energy with respect of the resonator means respectively.

In one embodiment the coupling means of the resonator apparatus consists only of a single input coupling means and a single output coupling means.

In one embodiment a plurality of input coupling means are provided and a plurality of output coupling means are provided for each resonator means. For example, two input coupling means could be provided and two output coupling means could be provided (i.e. four couplings in total per resonator means).

In one embodiment the input and output coupling means are arranged to provide capacitive or negative coupling with the resonator means.

In one embodiment the input and output coupling means are arranged to provide inductive or positive coupling with the resonator means.

In one embodiment one of the input and output coupling means are arranged to provide capacitive or negative coupling with the resonator means and the other of the input and output coupling means are arranged to provide inductive or positive coupling with the resonator means.

In one embodiment locating the input and/or output coupling means and the resonator means nearer a wall or side wall of the cavity compared to a centrally located resonator means provides an inductive coupling between the said coupling means and the resonator means.

In one embodiment locating the input and/or output coupling means and the resonator means a greater distance away from a wall or side wall of the cavity compared to a centrally located resonator means provides a capacitive coupling between the said coupling means and the resonator means.

In one embodiment the input and/or output coupling means arranged to provide inductive coupling includes a post. Preferably a longitudinal axis of the post is arranged parallel to or substantially parallel to a longitudinal axis, upright axis or height of the resonator means (i.e. the axis of protrusion of the resonator means from a wall of the resonant cavity).

In one embodiment the inductive coupling or post is integral with or attached to a wall of the cavity, such as for example a base wall or electrical ground plane of the resonant cavity.

Preferably the post is joined to or integral with the same wall of the resonant cavity to which the resonator means is provided on, integral with, joined to or supported on.

In one embodiment a coupling post can be provided which is not electrical grounded to the resonant cavity or is not in contact with a base wall or electrical ground plane of the resonant cavity. 'this coupling can be either capacitive or inductive depending on the mode of the resonator means.

In one embodiment the input and/or output coupling means arranged to provide capacitive coupling includes a disc or plate member.

In one example the disc or plate member is planar in form, and further preferably the major or main plane of the disc or plate member is arranged parallel or substantially parallel to a longitudinal axis, vertical axis or height of the resonator means (i.e the axis of protrusion of the resonator means from a wall of the resonant cavity).

In one example at least part of the disc or plate member has a curvature, and further preferably the curvature of the disc or plate member is the same or substantially the same as to curvature of the external surface of the resonator means which is opposite the same.

Preferably the disc or plate member is located a spaced distance apart from a base wall or electrical ground plane of the resonant cavity, in one example the disc or plate member is in contact with a side wall of the resonant cavity.

Preferably the post, disc and/or plate member are formed from, include and/or are provided with electrically conductive material such as for example metal or a metal coating.

Preferably the input and output coupling means are provided at 90 degrees or substantially 90 degrees to each other within the resonant cavity.

Preferably the input and/or output couplings can be made positive or negative by varying the distance of the coupling(s) and resonator means from the resonant cavity wall in which they are located.

In one embodiment the resonator means has two or more modes of operation. I;or example, the resonator means could be a. dual mode resonator or a triple mode resonator.

Preferably the two or more modes of operation of the resonator means include any of a transverse electromagnetic (TEM) mode, a quasi TEM mode, a pure transverse electric (TE) mode, a pure transverse magnetic (TM) mode, or a hybrid mode (HE or Eli) In one embodiment the two or more modes of operation of the resonator means are degenerate modes.

In one embodiment the two or more modes of operation of the resonator means include at least one non-degenerate mode.

Preferably the resonator means are any means or member which exhibits resonance or resonant behaviour at a particular frequency or frequency range.

in one embodiment the resonator means can be in the form of any or any combination of a rod, puck, post and/or the like.

Preferably the resonator mea.ns includes, is formed from or consists of dielectric material.

In one example the dielectric material is ceramic.

Preferably an electrically conductive coating is provided on part or whole of an external surface of the resonator means.

In one example the electrically conductive coating is naetaL Preferably the resonator means comprises one or more solid members, or one or more hollow members. In one example the resonator means could be a solid member with a channel defined therein.

Preferably the resonant cavity and/or the resonator means can have any cross-sectional shape and/or dimensions, such as for example circular, square, hexagonal and/or the like.

Preferably the shape of the resonant cavity is different to the shape of the resonator means.

Preferably the walls of the housing defining the resonant cavity are formed from or are coated in electrically conductive material, such as for example, metal or a. metal coating.

Preferably a first end of the resonator means is joined to" rests on or is integral with a wall defining the resonant cavity, such as for example a base wall of the cavity. However, the resonator means could be joined to or integrally formed with the lid or cover of the cavity or a side wall of the cavity.

Preferably the resonator means is joined to a wall of the resonant cavity via joining means, such as for example, any or any combination of solder, adhesive, welding, friction fit, push fit, one or more clips, screws, nuts and bolls, inter-engaging members and/or the like.

In one embodiment the resonator means is supported in the cavity via support means, said support means in the form of or including insulating material, such as for example Alumina.

In one embodiment one or more external side walls of the resonator means are provided with one or more grooves defined therein. The one or more grooves can be used to achieve a required coupling between the resonator means and the input and/or output coupling means in use. The grooves can also strengthen the coupling between the input and/or output coupling means and the resonator mea.ns by placing the coupling means in a. location with higher electrical field strength.

Preferably a longitudinal axis of the one or more grooves is provided parallel or substantially parallel to a longitudinal axis, vertical axis or height of the resonator means.

Preferably the longitudinal axis of the resonator means is the axis from which the resonator means protrudes from a wall of the resonant cavity.

Preferably a plurality of grooves are provided and these grooves are arranged a spaced distance apart around the external side walls of the resonator means.

Preferably the side walls of the resonator means are parallel to the side walls of the resonant cavity.

In one embodiment tunnig means arc provided with or associated with the resonator means of each resonant cavity.

Preferably the tuning means includes any means or mechanism to allow a change in the resonant frequency of the resonator means, such as for example a timing screw and/or the like Preferably the tuning means is offset with respect to the centre of the resonator means and/or resonant cavity.

Preferably the tuning means is centred with respect to the resonator means and/or resonant cavity.

In one embodiment the resonant cavity is defined between a base wall and side walls of a housing, and preferably a filter housing.

Preferably the resonant cavity has an opening and preferably the opening is opposite to the base wall.

Preferably a lid or cover is provided over the resonant cavity in use.

In determining an off-set position of the resonator means from a centre of the resonant cavity within the resonant cavity, when the cavity is viewed in top plan view, an intersection of an X-Axis and a Y-axis is located in the centre of the resonant cavity. When the centre of the resonator means is not located in the centre of the resonant cavity, the resonator means is said to be off-set.

In one embodiment if the resonator means and the input and output couplings are offset from the centre in a positive X-Y direction within the resonant cavity (i.e. the resonator has been moved in a northerly and easterly direction from the centre of the resonant cavity when the cavity is looked a.t in top plan view and north is towards the top of the page). Preferably the input and output coupling means are both inductive couplings, and further preferably the input a.nd output coupling mea.ns a.re located south and west of the resonator means, the one or more transmission zeroes are located above (Jr On the high side of the passband of the resonant apparatus.

In one embodiment if the resonator means and the input and output couplings are offset from the centre in a negative XX direction within the resonant cavity, the resonator has been moved in a southerly and westerly direction from the centre of the resonant cavity when the cavity is looked at in top plan view and north is towards the top of the page). Preferably the input and output coupling means are both inductive couplings, and further preferably the input and output couplings are located south and west of the resonator means, the one or more transmission zeroes are located below or on the low side of the passband of the resonant apparatus.

Preferably the resonant cavity is defined in a housing, and preferably is defined in a radio frequency (Rh) filter housing.

Preferably a plurality of resonant cavities are defined in the housing.

Preferably two or more of the resonant cavities are coupled together via c coupling means.

Preferably the cavity coupling means includes all iris or aperture located between adjacent resonant cavities, and/or by a transmission line.

According to a second aspect of the present invention there is provided a method of using resonator apparatus, said resonator apparatus including a resonant cavity defined in a housing, resonator means provided in the resonant cavity, the resonator apparatus including input coupling means provided a spaced distance apart from and opposite the resonator means, and output coupling means provided a spaced distance apart from and opposite the resonator means, the input coupling means being a spaced distance apart from the output coupling means within the resonant cavity, and wherein the method includes the step of arranging the resonator means so as to be offset from the centre of the resonant cavity, characterised in that the method further includes the step of arranging the distance of each of the input and output coupling means to the resonator means to be equal or substantially equal.

According to a third aspect of the present invention there is provided filter apparatus including resonator apparatus.

According to a fourth aspect of the present invention there is provided a method of using filter apparatus including resonator apparatus.

The present applicants have shown that the ratio between stored electric and magnetic fields of the resonator means change in the displacement volume of an off-centered resonator. The degeneracy of two modes of the resonator apparatus is disturbed, thereby resulting in a required bandpass filter response. The generated transmission zeroes can be placed on the high or low side of the band pass frequency of the filter depending on the direction of offset of the resonator means and the input and/or output coupling means within the resonant cavity.

At first glance, offsetting the resonator and/or coupling means with respect to the resonant cavity walls reduces the resonator Q factor due to an increase in surface current produced. However, the average Q factor remains almost constant in the case of non-degenerate triple mode filters.

The apparatus of the present Invention has been found to achieve greater than 30% fractional bandwidth compared to 15% fractional bandwidth in the prior art.

When the resonator means is centrally located within a resonant cavity, as per the prior art, a certain ratio is achieved between stored electric and magnetic energies within the air. gap between the resonator means and the resonant cavity wall. When the resonator means is moved to an off-centred or off set location within the resonant cavity, the ratio of stored electric and magnetic energies changes. Since the resonant frequency of the resonator means is determined by the ratio of stored electric and magnetic energies, then it follows that the resonant frequency can be changed as the resonator to wall offset distance is clranged.

rilbodiments of the present invention will now be described with reference to the following figures, wherein: Figures la-id show examples of the electric Held distribution of dual mode dielectric resonators with a cavity height of 20mm Figure la (Prior Art) is for a 11E11+ mode resonator where the resonator is located centrally of the resonant cavity; Figure lb is for a HE11+ mode resonator where the resonator is offset from the centre of the resonant cavity by 2mm; Figure lc (Prior Art) is for a I IEll -mode resonator where the resonator is located centrally of the resonant cavity; Figure Id is for a HE11-mode resonator where the resonator is offset from the centre of the resonant cavity by 2n-m; Figure 2 shows the resonant frequencies and Q factor of the dominant degenerate modes as a function of offset distance in nun; Figures 3a.-3h show different examples of resonator apparatus according to the present invention; Figures 4a and 4b (prior art) show a dual mode resonator in which the resonator is centrally located with respect to the resonant cavity and having 90 degree input and output inductive post couplings, and the resonant response of an electromagnetic simulation using the resonator in figure 4a respectively; Figures 5a and 5b show a dual mode resonator in which the resonator is off centred and located towards the left hand side/top cavity wall and having 90 degree input and output inductive post couplings, and the resonant response of an electromagnetic simulation using the resonator in figure 5a respectively; Figures Oa and 6b show a dual mode resonator in which the resonator is off centred and located away from the left hand side/top cavity wall and having 90 degree input and output inductive post couplings, and the resonant response of an electromagnetic simulation using the resonator in figure Oa respectively; I itigures 7a. and 7b (prior art) show a dual mode resonator in which the resonator is centrally located with respect to the resonant cavity and having 90 degree input and output capacitive plate couplings, and the resonant response of an electromagnetic simulation using the resonator in figure 7a respectively; Figures 8a and 8b show a dual mode resonator in which the resonator is off centred and located towards the left hand side/top cavity wall and having 90 degree input and output capacitive plate couplings, and the resonant response of an electromagnetic simulation using the resonator in figure 8a respectively; and I figures 9a and 9b show a dual mode resonator in which the resonator is off centred and located away from the left hand side/top cavity wall and having 90 degree input and output capacitive plate couplings, and the resonant response of an electromagnetic simulation using the resonator in figure 9a respectively.

Referring to figures 1a-Id, the electric field distribution of a dual mode dielectric resonator is shown. 't he dielectric resonator in this example is in the form of a dielectric ceramic puck 2 which rests on the base wall 4 of a resonant cavity 6. The resonant cavity 6 is defined within' an electrically conductive filter housing and also includes side walls 8 protruding outwardly from the base wall 4, and a lid 10 provided over an opening of the cavity and opposite to the base wall 4. The dual modes of the dielectric resonator are degenerate modes which are HI l 1 + and H 111 -. It is evident that the axial components of the degenerate modes is maximum near the top of the ceramic puck 2 since the first end 12 of the puck is short circuited via base wall 4. It is noted that the electric field is strongest adjacent the external resonator surfaces.

It can be seen that offsetting the puck 2 in a direction towards the cavity side wall 8 by as little as 2mm, as shown in figures lb and Id, results in disturbing the electric field of the resonant mode polarised in that direction. When the puck 2 is moved towards the cavity side wall 8, the change in resonant frequency of the puck 2 is proportional to the difference in stored electric imd magnetic energies within the displacement volume of the resonant cavity. If the stored electric energy is larger than the stored magnetic energy, then the resonant frequency of the puck 2 will decrease and vice versa.

In the immediate vicinity of the side wall 8 of the resonant cavity, the boundary condition requires the tangential electric field to be zero. Similarly as the puck 2 is moved closer to the side wall 8 of the resonant cavity, the tangential electric field outside the puck 2 that is required to be zero increases, i.e., the density of evanescent fields increases since the distance to a specified side wall is reduced. Thus, the closer the resonator is to the cavity wall, the higher the shift in the resonant frequency of the mode polarised in that direction. An off-centred dual-mode resonator results in an increase of loss of the mode polarised in the direction of offset. This is due to an increase in the appreciable produced surface currents in the cavity walls which will, in turn, reduce the Q factor of the resonator. By knowing how much the overall Q factor will deteriorate when offset, it becomes possible to select materials, shapes and a turn*); mechanism in a way that an optimum design is achieved.

Figure 2 shows the resonant frequencies and Q factor of the dominant degenerate modes as a function of the offset distance of a resonator from the centre of the resonant cavity with respect to the resonant cavity wall in mm Observing the frequency as a function of offset distance, where the cavity diameter is 30mm_ the resonator diameter is 20mm, the dielectric constant is 44, and the resonator offset ranges from -2.75mm to +2.75mm away from the centre, we conclude that moving the resonator towards the cavity wall does affect resonant frequency and Q factor of the mode polarised in that direction more than the other mode. However, the perturbation between the degenerate modes is not significant. This is due to the fact that most of the electric field is confined inside the dielectric puck. Higher perturbation may be obtained by using dielectric materials with lower permittivity or reshaping the resonator. It seems that this technique may be limited to narrowband bandpass filters using dual-mode resonators.

I figures 3a-3h show different examples (a non-exhaustive list) of how the resonator apparatus can be provided according to the present invention.

Figure 3a shows a side view of an offset resonator 102 having two inductive post couplings 112 attached to a base wall of the cavity 104 and launched from a side wall of the cavity.

i'igures 3b and 3c show a side view and a. top plan view of an offset resonator 102 having two capacitive probe couplings 112, 114 launched from a base wall of the cavity 104 respectively. The external side wall of the resonator is continuous and does not have grooves defined in the same. The resonator 102 is offset from the centre of the cavity 104 in the negative X and Y directions.

Figure 3d shows a perspective view of an offset resonator 102. The resonator has two capacitive probe couplings 112, 114 launched from a lid of the cavity 104. At least part of the coupling 112 is located within a. groove 116 provided on the external side wall of the resonator 102. A longitudinal axis of the groove 116 is parallel to a longitudinal axis of the resonator 102.

Figure 3e shows a perspective view of an offset resonator 102. 't he resonator has one capacitive probe coupling 114 launched from a base wall of the resonant cavity 104 and one inductive post coupling 112 launched from a side wall of the resonant cavity 104. At least part of the coupling 112 is located within a groove 116 provided on the external side wall of the resonator 102. A longitudinal axis of the groove 116 is parallel to a longitudinal axis of the resonator 102.

Figure 3f shows how two resonators 102, 102' located in two adjacent resonator cavities 104, 104' respectively can be coupled together at a dupkxing junction 110. The resonator 102 has two inductive post couplings 112, 114 launched from side walls of the cavity 104 to provide an input coupling and an output coupling respectively. The inductive post couplings are located within grooves 116 defined on the external side wall of the resonator 102. More grooves are provided than is required to accommodate the input and output couplings. A longitudinal axis of ea.ch groove 116 is arranged to be parallel to the longitudinal axis of the resonator 102. Resonator 102' is similar in form to resonator 102 but fewer grooves 116 are provided on the external side wall of the resonator 102' compared to that of resonator 102. 't his shows the different types of offset resonator can be successfully coupled together to provide a filter response in use.

Figures 3a and 3g show a side view and a top plan view of an offset resonator 102 having two inductive post couplings 112, 114 located in grooves 116 on the external side wall of the resonator respectively. The input and output couplings 112, 114 are launched from the side wall of the cavity 104. The resonator 102 is offset from the centre of the resonant cavity 104 in a. negative X-direction and a positive Y-direction.

Figure 3h shows a top plan view of an offset resonator 102 having two inductive post couplings 112, 114, located in grooves 116 on the external side wall of the resonator. The input and output couplings 112,114 are launched from the side wall of the cavity 104. The resonator 102 is offset from the centre of the resonant cavity 104 in a. negative X-direction and a negative \'-direction.

It is to be noted that some of the resonators can optionally have a metal disc 118 located on a top surface of the resonator to provide a different resonator response if required.

Figures 4a-9a show examples of a resonator 102 located at different positions within a resonant cavity 104, and corresponding figures 4b-9b show the resonant response of an electromagnetic simulation using the resonator in the resonant cavity in each case. In accordance with the present invention, the distance between the input coupling means and the resonator, and the distance between the output coupling means and the resonator is the same, irrespective of the amount and direction of offset distance from the centre of the resonator cavity.

The resonator 102 is a. dual-mode resonator and which has asymmetrically arranged 90 degree input and output couplings 106, 108. In figures 4a-6a, the input and output couplings are provided by inductive post couplings. ln figures 7a-9a, the input and output couplings are provided by capacitive plate couplings.

In the graphs of figures 4b-9b, Sil shows the reflection characteristics of the resonator in dB and 512 show the transmission characteristics of the resonator in dB. Tz =transmission zeros.

The graphs in figures 4b-9b show how by off-setting the resonator 102 within the resonant cavity, the position of the transmission zeros can be changed and/or the bandwidth of the filter's band pass can be controlled. Note that no additional coupling or tuning elements are introduced.

The direction of offset within the resonant cavity can be specified based on dividing the resonant cavity up when viewed in top plan view with the cross over of the X-axis and Y-axis passing through the centre of the resonant cavity.

For example, figures 5a and 8a shows the resonator offset in a negative X direction and a positive Y direction; figure 6a and 9a shows the resonator offset in a negative X and negative Y direction.

The same approach can be applied to triple mode resonators.

Claims

C 'aim s: 1. Resonator apparatus, said resonator apparatus including a resonant cavity defined in a housing, resonator means provided in the resonant cavity, the resonator apparatus including input coupling means provided a spaced distance apart from and opposite the resonator means, and output coupling means provided a spaced distance apart from and opposite the resonator means, the input coupling means being a spaced distance apart from the output coupling means within the resonant cavity, the resonator means being offset from the centre of the resonant cavity, characterised in that the distance of each of the input a.nd output coupling means to the resonator means is equal or substantially equal.
Resonator apparatus according to claim 1, wherein the resonator means and/or the coupling means are asymmetrically located within the resonant cavity.
3. Resonator apparatus according to claim 1, wherein a single input coupling means and a single output coupling means are associated with a single resonant cavity only.
4. Resonator apparatus according to claim 1, wherein a plurality of input coupling means and a. plurality of output coupling means are provided with a single resonant cavity.
Resonator apparatus according to claim 1, wherein the input and output coupling means are arranged to provide capacitive or negative coupling with the resonator means, wherein the input and output coupling means are arranged to provide inductive or positive coupling with the resonator means or one of the input and output coupling means are arranged to provide capacitive or negative coupling with the resonator means and the other of the input and output coupling means are arranged to provide inductive or positive coupling with the resonator means.
6. Resonator apparatus accordhig, to claim 1 wherein the location of the input and/or output coupling means and the resonator means nearer to a wall or side wall of the resonant cavity compared to a centrally located resonator means provides an inductive coupling between said coupling means and the resonator means.
7. Resonator apparatus according to claim 1 whercin the location of the input and/or output coupling means and the resonator means a greater distance from a wall or side wall of the resonant cavity compared to a centrally located resonator means provides a capacitive coupling between said coupling means and the resonator means.
8. Resonator apparatus according to claim 1 wherein the input and/or output coupling means arranged to provide an inductive coupling includes a post, and a longitudinal axis of the post is arranged to be parallel to substantially parallel to a longitudinal axis, upright a.xis or height of the resonator means.
9. Resonator apparatus according to claim 1 wherein the input and/or output coupling means are arranged to provide a capacitive coupling includes a disc or plate member, and a main plane of the disc or plate member is arranged to be parallel to or substantially parallel to a longitudinal axis, upright axis or height of the resonator means.
10. Resonator apparatus according to claim I wherein the input and/or output coupling means are arranged to provide a capacitive coupling includes a. disc or plate member, and at least part of the disc or plate member has a curvature which is the same or substantially the same as a curvature of an external surface of the resonator means which is opposite the same.
11. Resonator apparatus according to claims 9 or 10 wherein the disc or plate member is located a spaced distance from a base wall or electrical ground plane of the resonant cavity.
12. Resonator apparatus according to claim 1 wherein the input and output coupling means are provided at 90 degrees or substantially 90 degrees to each other within the resonant cavity.
13. Resonator apparatus according to claim 1 wherein the resonator means has two or more modes of operation, is a dual mode resonator or is a triple mode resonator.
14. Resonator apparatus according to claim 13 wherein the two or more modes of operation of the resonator means include any of a transverse electromagnetic (TEM) mode, a quasi TEM mode, a pure transverse electric Clip mode, a pure transverse magnetic (4M) mode, or a hybrid mode (HE or EH).
15. Resonator apparatus according to claim 13 wherein the two or more modes of operation of the resonator means are degenerate modes, or includes at least one non-degenerate mode.
16. Resonator apparatus according to claim 1 wherein the resonator means is any or any combination of a rod, puck, post, is formed from or consists of dielectric material and/or is ceramic.
17. Resonator apparatus according to claim 1 wherein one or more external walls of the resonator means are provided with one or more grooves defined therein.
18. Resonator apparatus according to claim 17 wherein a. longitudinal axis of the one or more grooves is parallel to substantially parallel to a longitudinal axis, vertical axis or height of the resonator means.
19. Resonator apparatus according to claim 1 wherein tuning means are provided with or associated with the resonator means of each resonant cavity, said tuning means being offset or centrally located with respect to the centre of the resonator means and/or resonant cavity.
20. Resonator apparatus according to clann 1 wherein the resonator means and the input and output couplings are offset from a centre of the resonant cavity in a positive X-Y direction.
21. Resonator apparatus according to claim 1 wherein the resonator means and the input and output couplings are offset from a centre of the resonant cavity in a negative X-Y direction.
22.A method of using resonator apparatus, said resonator apparatus including a resonant cavity defined in a housing, resonator means provided in the resonant cavity, the resonator apparatus including input coupling means provided a spaced distance apart from and opposite the resonator means, and output coupling means provided a spaced distance apart from and opposite the resonator means, the input coupling means being a spaced distance apart from the output coupling means within the resonant cavity, and wherein the method includes the step of arranging the resonator means so as to be offset from the centre of the resonant cavity, characterised in that the method further includes the step of arranging the distance of each of the input and output coupling means to the resonator means to be equal (Jr substantially equal.