GB2579425A - Phase or frequency tuneable RF device exploiting properties of sma #03_3 - Google Patents

Abstract

A phase or frequency tuneable device (e.g. an RF tuneable filter) has an RF cavity. An actuator formed of Shape Memory Alloy (SMA) material is used with the phase or frequency tuneable device to control the movement or deformation of the walls of the RF cavity or control the movement or deformation of additional electromagnetic structures in the vicinity of or inside the RF cavity. This movement or deformation of these elements affects the electric and/or magnetic components of one or several of the eigenmodes of electromagnetic field supported by the RF cavity. There may be two or more of the phase or frequency tuneable devices which are electromagnetically coupled, and the electromagnetic couplings may be in the form of irises which penetrate the solid walls or ground planes separating the tuneable devices. The phase or frequency tuneable device may contain a tuning device comprising the SMA material in the shape or wires, ribbons or sheets. The tuneable device may contain dielectric resonators.

Description

TITLE: Phase or Frequency Tuneable RF Device Exploiting Properties of S1VIA #03_3 DESCRIPTION

The Field of the Invention and the Prior Art

RF/Microwave (hereafter just RF) cavities and filters are known in the art, as are tuned filters, tuneable filters and adjustable cavities. Such a filter will have an input port and an output port (generically I/O-ports), sometimes coincident resulting in a single-port filter, and sometimes forming diplexers or multiplexers by having a common input port and two or more output ports. Recently, multiband filters arc being developed employing multiple resonances per resonator, or multiple resonators per cavity. Electromagnetically-coupled multi-cavity filters with a plurality of stages arc also known in the art wherein a sequence of cavities are electromagnetically coupled one to the next (in sequence) with possibly additional couplings between non-sequential cavities, and wherein the electromagnetic properties of one or more of the cavities arc individually tuned and sometimes dynamically tuneable (i.e. when in service), resulting in a multi-cavity filter which has much higher performance than that of any of its individual cavities. Filter performance may be measured as some combination of factors including pass-band insertion-loss (ideally zero), stop-band rejection (ideally infinite), phase-linearity (usually ideally perfectly linear with signal frequency), ripple (ideally zero), group delay and power handling (PIM, breakdown due to discharge in air, multipaction breakdown). Such filters arc typically of the low-pass, band-pass, band-stop, high-pass, phase-shift or all-pass configuration.

Where the filter is of bandpass or bandstop configuration it is characterised by a lower and upper cut-off frequency, the difference between which is called the bandwidth of the filter, and a "centre-frequency" between these two. A tuneable bandpass or bandstop filter will in general have a tuneable centre frequency and sometimes also a tuneable bandwidth. This may in practice be implemented by separately tunable lower and upper cut-off frequencies.

Such an RF filter can also be designed to produce primarily a phase shift, and in this case the useful effect of the cavity is to produce a phase difference dphi between that of the input signal and the output signal where dphi may be a tuneable quantity: i.e. in this case it is primarily the magnitude of phase-shift that is tuneable, and not the frequency at which the phase-shift occurs. Such a device is called a phase-shifting filter or just phase-shifter and an ideal phase-shifter would produce no change in insertion loss throughout the passband, and no change in insertion loss over the full range of tuneable dphi.

In some RF filters both a phase-shift function and a frequency-filtering function may be combined and both may be tuneable or specifically optimised. We use the tern filter to encompass all of these types of device.

RF cavities comprising chambers with solid conductive walls entirely surrounding the cavity are known in the art, as are RF cavities comprising a pair of often but not necessarily parallel, conductive ground-planes, and in the latter case individual cavities between the ground-planes may be delineated either by. I) solid conductive walls; or ii) by one or a plurality of conductive vias appropriately spaced and connecting between the ground-planes; or iii) by a combination of I) and ii). The input and output ports either: I) pierce the solid conductive cavity walls; or ii) are positioned between conductive vias connecting the ground-planes. Combinations of all of these types of RF cavities within the same filter are possible.

Physically adjacent cavities which are not necessarily sequentially adjacent cavities as far as the direct signal path through the filter is concerned, may be electromagnetically-coupled by Couplings. Each such Coupling may be comprised of: 1) one or more holes or "irises" passing right through the solid conductive walls separating the physically adjacent cavities; or ii) where the cavities are physically separated by one or more conductive vias connecting between the ground planes then by careful and appropriate positioning and spacing of the vias and again these Couplings are said to be formed by irises -gaps between vias; or iii) by coupling wires protruding into both cavities to be capacitively coupled when the wires are electrically isolated, or inductively coupled when the wires are connected to the inside of the cavity; or iv) by conductive tracks placed on an insulating layer on the inside or outside wall of one or both ground-planes protruding into each of the cavities to be coupled capacitively or inductively. Combinations of these types of Coupling within the same filter and even between the same cavities are possible.

The cavities may or may not contain one or more resonators. Typically a frequency-tuneable filter will have at least one cavity containing one or more resonators whereas a tuneable phase-shifter filter cavity may contain zero one or more resonators, and in the case where there is no resonator then instead a reflector is needed, and the phase-shifter may be realized with at least one side of the cavity being opened to a waveguide carrying the RF signal to be phase-shifted. The resonators maybe either conductive or dielectric or some combination of these. Each of any conductive resonators within a cavity may be either connected to ground at one end only or connected to ground at each end or connected to ground in the middle or connected to ground at one or more half-wavelength intervals or not be connected to ground at all resulting in a floating conductive resonator. The one or more cavities of a tunable phase-shifter filter may contain non-resonant components with one or more tuneable parameters the changing of which primarily effects the phase between input and output. In a simple phase-shifter filter the parameter might be the position of the non-resonant component in the cavity.

Typical of current filter state of the art is patent W02016/202687.

Completely electronic tuning of filters (i.e. involving no mechanical change of components) as described above is possible using semiconductor components (e.g. varactors, PIN diodes, FET switches). However, the RF losses (and associated RF noise production) associated with such electronic tuning components (such as varactor diodes which also introduce waveform distortion, intennodulation and cross-modulation products, and reduce power breakdown threshold) increase with RF frequency and are often unacceptable above the low 0Hz region, especially where the RF power budget is critical or where very low receiver noise is required. In these cases very high-Q mechanically tuned filters are necessary.

All of the above is known in the art.

The Problems with Low-Loss RF Tuneable Filters using the Prior Art We have described above some of the known prior art related to tuneable RF filters. The problems with current low-loss fully tuneable filters are that they are big, heavy, expensive to make and even more costly to actuate (i.e. to control dynamically in service). Conventional tuneable RF filters are primarily machined out of solid metal, usually aluminium, which is a slow and expensive process, even when using CNC machining. Such fabrication methods also restrict the geometric shapes that may be easily made -e.g. holes or cavities blind at both ends must be fabricated in sections and then assembled together with well-fitting precision joints required to be highly electrically conductive.

As far as actuation of moving mechanical components is concerned, rotary electric motors may be used but these motors are costly, bulky and require a significant amount of electronic control, and frequently also require a position sensor with related electronics to provide an accurate indication of the position of the moving component. Rotary electric motors also require some form of rotary-to-linear motion converter as well as a gearbox to produce the required component motions at the right speed, all of which add to the cost, size, weight and unreliability of the solution. Finally brushed electric motors are inherently unreliable and produce conductive particulate pollutants, whereas brushless motors are significantly more expensive and require more elaborate electronic control. Where a given tuneable filter has multiple tuning elements (often five or many more are required for high-performance) the cost of separately driving each of these elements is often prohibitive. Complicated schemes of mechanical linkages to drive multiple tuning elements with one motor might possibly reduce the cost but add to the complexity and unreliability, and are generally less flexible than individual clement tuning drives.

For example, in patent W02016/202687, because of RF energy leakage problems around metal tuning elements, the inventor is forced to instead use dielectric tuning elements. This is one of the problems we address below. Also in this same patent there is no teaching relevant to the integration of actuators to allow for programmable tuning (as opposed to manual tuning) and this is one of the primary issues we address below. Lastly, the coupling between cavities is fixed and not tuneable, and in what follows we advantageously address this issue also.

Co-owned patent applications GB20160003081 20160223 and W02017144873 (Al) 2017-08-31 describe in very general terms the application of SMA actuators to tuning RF devices. In what follows we supply much more practical detail about how to apply these novel techniques.

The Present Invention In the present invention we show how to overcome all of these problems of low-loss RF tuneable filters, by the use of electronically-controlled Shape Memory Alloy (SMA) actuators to move and or deform the tuning elements and/or the resonators and/or novel filter electromagnetic and mechanical configurations. A useful form of SMA actuator for these functions is an SMA wire actuator where the contraction of a long thin wire of SMA material is used to provide a pulling force upon heating of the wire above its Austenite start temperature. We refer hereafter to such actuators very broadly as SMA wire actuators. However, in certain instances it can also be useful to use SMA material in an actuator in forms other than wires, e.g. strips, sheets or even rods and bars. For convenience of description we include all such SMA actuator forms in the term "SMA wire" hereafter. In the present invention conventional tuning screws are replaced by moveable and/or deformable elements actuated by SMA wires. Both capacitive and inductive tuning elements (and combinations thereof) are used, and we tune not only the resonators to shift centre-frequencies, but also tune input-output (I/O) couplings, inter-cavity couplings, as well as the phase angle of predominantly phase-shifting elements.

By using one small SMA actuator (each with one or more wires, and where there is only one SMA wire in an actuator it is to be understood that some sort of mechanical spring force is used to achieve a return stroke, as is well known in the art of SMA actuators) to control each tunable element separately, we avoid complicated and unreliable mechanical mechanisms, gears and levers otherwise needed to keep multiple tuning elements in synchronisation (in.sync*). Instead the synchronisation is done entirely in electronics and/or software for maximum flexibility and minimum complexity. There may occasionally be instances where it is convenient and appropriate to move more than one tuning element with a single SMA actuator, and such cases are to be understood to be included herein, though it is our contention that the most advantage will usually be gained by separately controlling each tuneable element with a dedicated actuator ideally independently controlled by software.

However, one drawback of simple SMA actuators /1' SMA wire actuator is their long-term positional stability which is poor. Another is that to maintain their set position such actuators need to be powered continuously. Thirdly, their absolute positional precision is also suspect, at least over the long term, because of SMA material ageing, fatigue, as well as other factors. Fourthly, the greater the stroke required of a simple SMA actuator, the greater the length of SMA wire is required to achieve that stroke (all else being equal) and thus it is difficult to make compact SMA actuators with long stroke. Fifthly, for precise (even short-term) position-control a complex high-precision electronic controller is required (for each SMA wire) capable to accurately estimate the SMA wire resistance (from which the wire length and thus the actuator position is estimated) or, some other form of precision position sensor needs to be added, all of which adds considerable size, power consumption, complexity and cost. Another co-owned patent (GB1819576.8) overcomes all of these problems, by creating a new form of SMA actuator, which we call an SMA-stepper-actuator. The key features of this new form of SMA actuator are: zero-power position hold; required total SMA wire-length is independent of actuator stroke; near-ideal short-and long-term positional stability, unaffected by material ageing and fatigue; very high positional precision; simple electronic control with no need for precision ADC and DAC components. In what follows in the description, claims and abstract, and drawings of the present invention, it is to be understood that wherever any form of SMA actuator or SMA wire actuator or SMA-wire actuator is mentioned or shown below in what follows as part of a functional description or an embodiment or claim of the present invention, then an SMA-stepper-actuator (in any of the forms described in GB1819576.8) may advantageously be substituted, because of the exemplary features of this particular form of SMA actuator set out above (it was specifically invented to overcome the issues described above), and all such substitutions are to be considered as included in this invention. This is particularly relevant to the control of RF devices, since frequency-and phase-stability are generally one of the most critical parameters of such devices. Making such an RF device tuneable in some way (as we here describe using SMA actuators) in no way diminishes that requirement for stability, of which ever parameter(s) has been tuned. Where specific descriptions below refer to the actual mechanics of the SMA wire itself (e.g. when describing using twisted-pairs of SMA wire, or using insulated SMA wire) then they can additionally be read as referring to the SMA wire(s) within an SMA-stepper-actuator where that option is being considered as the specific form of (generic) SMA wire actuator.

Algorithms and/or look-up-tables (LUTs) in a controller determine how each tunable element and its associated actuator needs to be moved or deformed to achieve the desired filter performance and then further algorithms are used to separately control all of the actuators in parallel to provide optimum performance. By having the same controller monitor the temperature inside the tunable cavities and modulate the actuator control algorithms accordingly, the control system is also able to temperature-compensate the whole filter against environmental conditions as well as heat build up within the system.

Within the tuneable filter are one or more components or elements whose properties may be changed by moving or deforming them, or both. These are generically designated as tuneable elements hereafter. A tuneable element maybe a component specifically introduced solely to tune another electromagnetic component (such as a resonator, or a coupling device or a tapping point), or may be one of these electromagnetic components themselves in the case that the electromagnetic properties of that component may be changed by an external effect (e.g. mechanical force, which might be used to move or deform the electromagnetic component).

The SMA actuators themselves can be small and can be very low-cost, may require no lubricants, are highly reliable, are frequently silent and generate no significant magnetic fields. Such an SMA actuator may be mounted outside an RF cavity and control its respective tuneable element via a mechanical connection to the tuneable element inside the cavity; alternatively the tuneable element itself may be extended to protrude through the cavity to the outside and become an integral part of the external actuator.

Because the SMA wires are so small -typically only 25microns (25pm) in diameter for the roles envisaged herein -the SMA actuators may advantageously be positioned right inside the RF cavities or waveguides if suitable precautions arc taken, and the SMA actuator can then be designed to be mechanically integral with the tuneable element to be controlled. To put this in perspective, the total volume of an SMA wire actuator made from even a 20mm length of 25pm wire is less than 1/100th of a cubic millimetre, i.e. < 0.01mm3 and yet such an actuator can pull a -10gm tol5gm load a distance or stroke of 0 75mm or more, which stroke can be greatly increased by use of suitable mechanical leverage techniques (or the inventions described in co-owned patent GB1819576.8), which in some forms may reduce the force by the same ratio. Such tiny, relatively high-force, actuators positioned within the RF cavities can be highly beneficial in terms of reducing overall filter size, reducing the RF leakage otherwise encouraged by moving mechanical devices penetrating the walls of the RF cavities, reducing the amount of structure necessary to support and house the actuators (i.e. no additional housing at all is needed if all of the actuators are sited within the RF cavities) as well as reduce the mechanical loads the SMA actuators are required to move, because of the elimination of coupling mechanics and in many cases sliding supports and additional friction as well. No other form of actuator is as versatile or well suited to this tuning task as small SMA actuators, because the high-force small-volume very high reliability characteristics of SMA actuators is unmatched. MEMS and electrostatic actuators fail on one or more of stroke, force and reliability. Other electric motors are simply too big, too expensive, too unreliable or some combination of these to be usefully fitted within the waveguides or cavities.

Further innovations made possible by this use of small SMA actuators especially when closely integrated with the filter structures themselves are the use of thin glass dielectric wafers and corundum (ATO, crystalline aluminium oxide) dielectric layers grown directly onto aluminium components in novel ways particularly to increase the tuning effect of the tuning elements, thin blade-shaped or ribbon-shaped tuning elements instead of cylindrical tuning screws and plungers, integral RF chokes positioned along the lengths of conductive tuning elements where they do protrude through cavity walls, and the use of shape-changing of RF elements. Where the material of a tuning element within the cavity either extends through the cavity wall or is mechanically connected to the outside of the cavity by some connective structure this will in general produce a leak-path for RF energy to escape from the cavity. By suitably shaping this structure to produce capacitive and inductive sections an integral RF choke can be created that will completely eliminate such RF leakage. In conventional tunable filters the resonators and couplings are mechanically fixed-shaped components with galvanic contacts implemented for electrically connecting the tuning pins, and generally only the positions or rather the lengths of the tuning elements, if anything, changes. The provision of small internal (to the cavities) SMA actuators or actuator wires allows the resonator and tuning element components themselves to be mechanically deformed by the contraction and expansion of SMA wires when suitably arranged and attached. Thus, a resonator, e.g. that may conventionally have been structured as a rigid rod of metal, may now be structured as a thin conductive strip (but still considerably thicker than RF skin-depth and therefore of similarly low loss) which is easily bent by the pull of an SMA wire or SMA actuator mechanically attached at one end to some point on the resonator and to a ground plane (or in some instances to a different point on the same component) at the other. Because in the active region of the SMA wire it contracts with increased heating, if the heating in the wire is induced by an electrical current in the wire and the metal of the resonator is used as the return path for the current, then the resonator made of normal metal (i.e. not SMA) will expand slightly with increasing current, thus increasing the overall bending effect of the resonator/SMA-wire combination.

So in the present invention an RF filter has one or a plurality of stages, and the filter is either, I) tuneable between upper and lower frequency limits and is a low-pass, band-pass, band-stop or high-pass configuration, or ii) produces a tuneable phase shift, or iii) both of these. The RF filter adjacent stages are electromagnetically coupled. The filter is either constructed of two or more spaced preferably parallel conductive ground planes (though non-parallel ground planes can also be used) with solid conductive joining walls connecting between the conductive planes and/or with conductive vias positioned between the conductive planes, and has inside and between the ground planes one or a plurality of separate cavities separated by either solid conductive partitions or by walls formed by a plurality of conductive vias positioned between the conductive planes or by both, and in each of those cavities is zero, one or a plurality of resonators.

The resonators may be either conductive or dielectric or some combination of these. Each of any conductive resonators in a cavity may be either connected to ground at one end only or connected to ground at each end or connected to ground in the middle or connected to ground at one or more half wavelength intervals or not be connected to ground at all resulting in a floating conductive resonator.

One or more of the cavities has each either one or more mechanically moveable or deformable resonators, or one or more deformable or movably mounted tuning elements penetrating into or wholly contained within the cavity such that the deformation or movement of the tuning element changes the electromagnetic characteristics of the cavity. The moveable or deformable resonators are caused to move or deform each by an associated SMA-wire actuator. The tuning clement or elements are caused to deform or move each by an associated SMA-wire actuator.

In the case that the conductive ground planes are electrically connected by conductive vias then the spacing between the vias is chosen to produce the required degree of coupling including zero coupling between any cavities separated by the vias or between any cavities and the outside of the filter delineated by the vias. Each of the conductive vias between the ground planes may be either connected to a ground plane at each end or connected to one ground plane at one end only resulting in a blind via with one end left open-circuit or be connected to no ground plane at either end resulting in a buried floating via (with both ends left open-circuit).

A tuneable cavity either contains one or more tuneable resonators thereby giving that cavity a degree of tuneable frequency selectivity, or instead, a tuneable cavity contains no resonator in which case it can have very high Q and be very frequency selective. By employing the TEM eigenmode that has no cut-off the addition of a resonator to a cavity need barely reduce the outline dimensions of a cavity. In the case where there is no resonator in a cavity it may advantageously be used as a tuneable phase-shifter by incorporating one or more tuneable reflector elements instead, which may be tuned by movement or deformation thereof. However, a tuneable phase-shifter filter cavity may also contain one or more resonators depending on the required electrical dimensions and the particular intended operating mode to be employed.

In a multistage tuneable filter where each stage is implemented by one or more tuneable cavities there is generally one primary path through the filter stages in a certain sequence from the input port to the output port, although in more complex filters there may also be secondary signal paths as well. Stages or cavities which are sequential along that primary signal path are referred to here as path-adjacent stages or path-adjacent cavities, to distinguish them from merely physically-adjacent (here called adjacent) stages or cavities. Path-adjacent cavities are coupled to each other by Couplings where the strength of each Coupling can be between zero (no coupling) and one (fully coupled). In addition to path-adjacent cavity couplings, there may also be additional couplings between adjacent but not path-adjacent cavities and such couplings are also referred to as Couplings. These non-pathadjacent cavity Couplings may be used to implement more complex filters with more desirable filter characteristics. Such techniques are well explained in several well established theoretical works, for example: George L. Matthaei, L. Young, E.M.T. Jones, "Microwave Filters, Impedance-matching Networks and Coupling Structures"; Richard J. Cameron, Raafat Mansour, Chandra M. Kudsia, "Microwave Filters for Communication Systems: Fundamentals., Design and Applications".

Where two coupled cavities are separated by a solid conductive partition then the Coupling is formed by one or more appropriate sized apertures cutting through that conductive partition and the Coupling response is related to the cavity separation distance and size and shape of the coupling aperture(s). Where two coupled cavities arc separated by a plurality of conductive vias in the region between the cavities to be coupled, then the Coupling is formed by strategically locating gaps and the sizes of gaps between these vias and the number, position and dimension of the vias around the gaps define the amount of coupling between adjacent cavities. Alternatively, the Coupling is formed by providing additional non-grounded conductive tracks printed on an insulating layer formed on the inside of one or both of the ground planes or cavity walls sandwiching the cavities to be coupled, and the conductive tracks protrude into both of the adjacent cavities without electrically connection to anything else. Alternatively, the Coupling is formed by non-grounded cross-coupling wires protruding into both of the adjacent cavities without electrically connection to anything else. Both of these Couplings are capacitive in nature. If instead the tracks or wires are grounded at both ends then such a Coupling becomes inductive instead. Coupling may also be achieved by some combination of these coupling techniques.

The resonators arc made of conductive material or are made of low-loss dielectric material or are made of non-conductive material coated or plated with conductive material or are made of some combination of these. The dielectric resonators arc preferably made of high permittivity low loss RF ceramic. One or more of the resonators are in the form of strips or T-shaped strips or rings or spirals or crosses or other shapes that resonate at the required frequency. In one variant of the present invention the cross-section of the resonator is such that it is easy to bend or flex elastically in at least one dimension, e.g. a thin strip of metal or metal iced plastic or laminate. Where a resonator has a geometry with several cigenmodes (e.g. X-shaped or star-shaped) then concurrent modes in the resonator may be suppressed by shorting to ground the corresponding ends or points of the branches of the resonator structure. A more compact assembly can be achieved with a dual-mode resonator or a triple-mode resonator with a minimum of two or three mutually orthogonal branches with a single common point. Such an orthogonal three branch resonator necessarily has a 3D configuration and in this case at least one of the three branches may protrude through one of the ground planes if their spacing is too close to fully contain the 3D resonator. Alternatively multi-mode waveguide cavities can also be employed where orthogonality of modes is enforced by the boundary conditions on the walls and the degree of symmetry in the cavity.

External signal connections are provided in the form of input and output tapping points to the first (input) and the last (output) cavity, where there is only one cavity, then it becomes both the input (first) and the output (last) cavity, i.e. the first is the same as the last. Where there is a resonator in the cavity being tapped then the tapping point is preferably adjacent to that resonator; where there is no resonator in the cavity being tapped (e.g. if this is a phase-shifter cavity) then the tapping point is into the cavity itself, e.g. a waveguide port.

So a tunable filter of the present invention has an input port, an input tapping point, one or more cavities at least one of which is tuneable, and where more than one cavity, then one or more Couplings, zero or more resonators, an output tapping point, and an output port, which may be the same port as the input port.

At least one electromagnetic element (input tap, cavity, resonator, Coupling, or output tap) of the tunable filter is tuneable, either by physically changing its shape (by deformation), or by moving it relative to the filter body i.e. the ground planes, or by the provision of an adjacent changeable tuning element. A tuning clement operates to tune its associated electromagnetic element by moving relative to it, and it may do this either by whole-body movement of the tuning element or by deformation of the tuning element such that the portion of the tuning element close to the electromagnetic element moves relative to it or relative to a ground plane, or to both.

Where an electromagnetic element or tuning element operates to tune by virtue of deformation, then that element may advantageously be contained wholly within the cavity that it tunes, thus avoiding the need to provide for moving structures to penetrate the cavity walls.

Where a tuning element operates to tune by virtue of movement relative to an electromagnetic element (input tap, cavity, resonator, Coupling, or output tap) of the tunable filter, then that tuning element is movably mounted and either penetrates into the cavity being tuned or is wholly contained within that cavity.

In both the case of deforming elements and the case of moveably mounted tuning elements, the tuning effect comes about because the movement changes the capacitive loading or inductive loading or both of the associated electromagnetic element.

The effectiveness of moving or deforming a tuning clement to tune its associated electromagnetic element may advantageously be enhanced by interspersing a thin dielectric material into the space between the tuning element and the electromagnetic clement to be tuned. A thin glass wafer is a suitable dielectric material in a suitable form for this function. However, such glass wafer thicknesses are limited to about 300um or greater because of manufacturing and handling issues. An alternative and much superior effect can be obtained by making from aluminium, either the conductive part of the element to be tuned (or at least the portion of it adjacent to the tuning clement) or instead, the tuning element itself, and growing a thin smooth crystalline layer of corundum (crystalline A120,) on the aluminium surface between the tuning element and element to be tuned. Such layers may have useful thickness in the range 1 to 30um (thicker layers are possible but become increasingly difficult to maintain the quality of the dielectric), have typical dielectric breakdown voltage of >16KV/mm, high dielectric constant of -9.8 (g.,1MHz), and very low RF loss with dissipation factor as low as 0.0002. If the aluminium surface to be oxidised is first polished then the resulting corundum coating grown upon it also has an external surface of more or less the same surface finish (i.e. almost polished) which allows intimate and low friction contact between it and the adjacent clement.

Similarly when an electromagnetic element is self-tuned by deforming it the effectiveness of such tuning may be enhanced by the suitable insertion of a dielectric element, such as a glass wafer or corundum coating on one of the adjacent surfaces, between the moving part of the deformed element and an adjacent ground plane.

Depending on the performance requirements of the tunable filter, any, some, or all of the electromagnetic elements of the filter may be provided with such a deforming or movably mounted tuning element, or alternatively may themselves be constructed so as to be easily deformable or moveable and be tuned by virtue of such deformations or movement of the electromagnetic element.

Each tuning element may have the shape of a flat strip, or a rod, or a bar, or a tube, or more generally a long prismatic section with flat or curved or corrugated surfaces, but preferably a shape such as a thin flat strip is used to reduce the mass and volume of the tuning element, making it both easier to move with a small SMA wire actuator, and easier to fit inside a compact filter structure with multiple tuning elements.

The tuning elements are made of conductive material or are made of low-loss dielectric material or arc made of non-conductive material coated or plated with conductive material or are made of some combination of these. Dielectric tuning elements are preferably made of high permittivity low loss RF ceramic or alternatively are made from a glass wafer.

A tuning element is preferably aligned in the same direction of greatest extension as the resonator it is tuning so that the gap between the tuning element and the resonator is also aligned with the resonator. For example, where a resonator is in the form of a rectangular section prismatic bar with a greater width than thickness, then the associated tuning element would preferably be in the form of a thin strip having a width similar to the width of the resonator, be positioned close to and parallel to the wide face of the resonator, and have its long axis aligned parallel to the long axis of the resonator, so that progressive movement of the tuning element in this axial direction would cause progressively increasing or decreasing overlap of the resonator by the tuning element and thus increasing or decreasing capacitance. This affords a large range of tuneability with nearly linear tuning characteristics.

A resonator may have a longitudinal slot or slots in it into which a tuning element may fit without touching the resonator, to increase the variability of capacitance between the tuning pin and resonator. A resonator may have a longitudinal slot or slots in it into which a tuning element may fit without touching the resonator, to increase the variability of self-inductance per unit of length of the resonator.

Each tuning element may either be entirely contained within the RF cavity, or alternatively may extend through an aperture in the cavity wall and even further to the outside region beyond. In this context we mean by RF choke an additional auxiliary fixed low-pass filter with a stop-band covering at least the entire operating bandwidth over the full tuning range of the main tuneable filter. In the case that a tuning element is electrically conductive and extends beyond the cavity wall, then RF isolation for the portion of the element protruding outside the RF cavity can be provided by integrating an RF choke into the structure of the tuning element around the region where it exits the cavity and enters the cavity wall and optionally beyond. A simple low-pass RF choke may be realised by a capacitive load at the external end of the tuning element sufficiently large to be considered an RF short. A more effective RF choke may be formed by a sequence or series of one or more inductive sections each followed by a parallel capacitive section positioned down the length of the tuning element from the cavity to the external end of the element. The inductive sections may be fabricated by making this section of the tuning element narrow, and the capacitive sections by making them wide. Thus a series of suitably sized and spaced notches cut in one or both sides of a wide, thin, flat tuning element along its length in the region in and around where it passes through the RF cavity wall together with close proximity of this region to at least one grounded surface for capacitive coupling, can be arranged to completely stop RF leakage out of the cavity via the tuning element. The provision of such an RF choke on a tuning element reflects the majority of the RF energy in the cavity incident on the internal end of the tuning element back into the RF cavity, which effectively increases the Q of the cavity, or equivalently, lowers the RF loss associated with the tuning element.

The one or more tunable elements of the tunable filter of the present invention are caused to move or deform (shape change) by one or more Actuators (defined below), with one or more of the tunable elements sharing an Actuator, so that the number of Actuators can vary from one, where all of the tunable elements are moved by the same Actuator, up to the number N of tunable elements where each tunable element is driven independently of all of the others by its own Actuator. Preferably there is a separate Actuator provided to independently control each tuneable element, so that there are N Actuators.

An Actuator is herein defined to be an SMA actuator, with the SMA material in the form of a thin wire, strip, or sheet. The most preferable forms of Actuator SMA actuator are: i) any of the forms of SMA-Stepper-actuator described in co-owned patent GB1819576.8; and ii) an SMA-wire actuator where the length of one or more sections of SMA wire are caused controllably to change by controllably changing the SMA wire temperature(s). The temperature of an SMA wire may advantageously be changed by controlling the magnitude of electric current passing through the SMA wire. This electric current in turn is preferably under the control of a programmable device such as a microprocessor. The length-changing SMA elements (e.g. wire or wires, strips or sheets, or the body and output element of a SMAstepper-actuator) are then mechanically connected either directly or indirectly between the filter body and the moveable or deformable tuneable elements of the tuneable filter, which causes the tuneable elements to move relative to the filter body or to change their shape (deform). For a deformable tuneable element the length-changing SMA element(s) may instead be mechanically connected between two (or more) separate points on the deformable tuneable element itself, which causes the tuneable element to change its shape (i.e. deform).

The mechanical linkage of a tuneable element to its respective Actuator may be direct and immediate, in which case there is no independent mechanical coupling component between the tuneable element and the Actuator. In a fully integrated Actuator, part of the tuneable element itself may be used as part of the Actuator structure and there then will be no discernibly separate Actuator and tuneable element, but instead a single component with moveable or deformable parts capable of changing the electromagnetic environment within a cavity or between cavities. So the tuneable element may optionally and preferably be integral with the Actuator structure.

Each Actuator connected to one or more of its respective tuneable elements may be positioned outside of the RF cavity or cavities of its tuneable element(s), or may instead be positioned within the walls of the RF cavity or cavities, or instead be placed partially or wholly within the RF cavity or cavities.

Where any tuneable element is made of a dielectric material and its associated Actuator is not wholly separated from the inside of a respective cavity or cavities by the solid conductive wall of the cavity(s) it may be RF electrically isolated by the positioning suitably close to the tuneable element of one or more conductive vias connecting between the conductive walls of the cavity(s). In particular, straddling the tuning element with conductive vias spaced closer than a half wavelength of the highest operational frequency of the filter in this way, will eliminate RF leakage via the dielectric element.

Where any tunable element is made of a conductive material and protrudes through a cavity wall then to prevent TEM mode propagation along the tuning element of RF energy from within the cavity to the outside of the cavity and towards its associated Actuator, two or more buried vias are located adjacent to and along the longitudinal line of the tuning element and separated by the appropriate interval which is approximately a half-wavelength but corrected for the reactance introduced by the adjacent vias. This is sufficient for the propagation at this wavelength to be blocked by capacitively loading the leaking TEM mode, and will completely stop the leakage.

In the case that more than one Actuator in total controls the movement of the totality of tunable elements, then the synchronisation of the movements of all of the tunable elements is electrically controlled by the synchronisation of the appropriate control signals to the plurality of Actuators, for example by means of a pre-computed look-up table kept in the memory of the controller or by a real-time algorithm generating the actual required positions of all tunable elements to achieve the required state of the filter.

If the tuning elements are each movably supported by a tuning support structure (Support) which may be partially or fully dielectric or partially or fully conductive, then each tuning element is associated with at least one SMA wire, and is mechanically connected directly or indirectly to that wire such that changes in length of the SMA wire caused by heating and cooling of the SMA wire cause changes in position or shape of the tuning element. In this case each SMA wire may be enclosed within a dedicated void in one of the one or more Supports to ensure free movement of the SMA wire relative to the Support. Each tuning element is then positioned slidably in a channel through the Support to ensure free movement of the tuning element while maintaining a precise gap between and accurate distance from the tuning clement to the corresponding resonator, Coupling or tapping point for all positions of the tuning element controlled by the Actuator. Each such Actuator may be fully integrated into the filter, for example by being buried inside the Support.

A resonator is preferably mechanically fixed relative to the ground planes and is not moveable. In an alternative variant of the present invention a resonator may be movably mounted within a cavity and caused to so move by mechanical connection to an Actuator in which case the resonator becomes itself a tuneable element. In a further alternative variant, a resonator may be constructed so as to be easily mechanically deformable and is caused to so deform by mechanical connection to an Actuator which then applies stress to the resonator in which case the resonator becomes itself a tuneable element. Viable deformable resonator forms include thin strips, flat-section spirals, flat-section helices, bellows and other shapes which have at least one direction of easy (low force) deformation.

Optionally there may be more than two parallel or near-parallel ground planes and in this case there may be openings in any ground plane that separates at least two other ground planes to form either inductive and/or capacitive cross Couplings between physically adjacent cavities on either side of that separator ground plane. These coupled cavities may contain one or more resonators tuned by one or more tuning elements actuated by Actuators, and such cross Couplings themselves may also preferably be tuned by one or more tuning elements each actuated (to move or deform) by an Actuator.

A filter so constructed within three or more ground planes is called a 3D Folded filter. In such a Folded filter where there is only one cross Coupling (i.e. through a ground plane) then the filter topology is no different to non-folded filters, and topologies are limited to Chebyshev filters (defined by a diagonal coupling matrix). A 3D Folded filter with more than one cross Coupling (i.e. through a ground plane) allows more complex filter topologies to be realised including elliptical filters, extracted pole filters and other types, characterised by a generalised coupling matrix with non-diagonal non-zero elements.

In conjunction with the use of multiple vias to separate and connect the ground planes more complicated tuneable filter topologies become possible while still being compatible with SMA actuated tuning elements, as the filter may now be folded in 3D. This in turn allows for tuneable couplings between non-path-adjacent cavities which may now become physically-adjacent in 3D, which enables the realisation of for example fully tuneable elliptical filters. Such topologies make the manufacture of these structures more compatible with 3D printing and with 2.5D processes such as PCB and microstrip technology and wafer level integration potentially allowing fully printed designs for dramatic cost saving.

Such topologies may also be manufactured by CNC machining in solid metal when high power handling and low PIM requirements dictate.

Using multiple stacked ground planes and multiply folded filters with several levels of cross-coupling may advantageously be used to modify the overall volume of a filter with given performance characteristic, and because of the greater flexibility in defining the elements of the coupling matrix can better optimise performance parameters such as group delay equalization.

In a filter with just two ground planes it is nonetheless still possible to construct a 2D Folded filter wherein a sequence of coupled cavities folds back on itself within the space between the ground planes (e.g. serpentine-like) making some non-path-adjacent cavities nonetheless physically adjacent and thus allowing the possibility of additional Couplings to be made between these non-path-adjacent but physically adjacent cavities, with each of these additional Couplings being optionally controllable with a tuning element moveable by an Actuator. Such a 2D tuneable Folded filter is capable of realizing at least some filter topologies with non-zero non-diagonal elements in their coupling matrix.

Where at least the portion of a tuning element outside of a cavity is non-conducting (e.g. dielectric, or insulator not coated or plated with conductive materials) then the at least one SMA wires that change the position of that tuning element may be attached directly to it. For tuning elements with only conductive portions outside of a cavity, then the at least one SMA wires that change the position of that tuning element may be attached to it via an electrically insulating structure, e.g. plastic or ceramic, to electrically isolate the SMA wire heating current from the tuning element.

Where the section of a tuning element outside a cavity, the Tail, is conductive it may be RF isolated from the RF energy within the cavity by: a) an intrinsic RF choke formed along the length of the tuning element wherein the longitudinal extent of the element provides a series inductance and the proximity of the Tail to adjacent ground planes provides a parallel capacitance; and/or b) an at least 2-section RF choke, similarly formed as in a) by shaping the profile of the tuning element in the Tail region so that it comprises successive wider and narrower sections electrically in series along the length of the element, the wider sections being predominantly capacitive and low impedance, the narrower sections being predominantly inductive and high impedance. With this arrangement advantageously, the SMA wire or wires provided to cause motion of the tuning clement, may be attached to the low-impedance capacitive sections of the so-shaped Tail so as to maximally isolate them from any RF energy transmitted from within the cavity; such series inductive / capacitive/inductive/capacitive series sections effectively form a multi-section RF choke or low pass filter.

Where the tunable filter is constructed between 2 or more ground planes, then the conductive ground planes are preferably parallel.

IAn Actuator of the tunable filter may advantageously be positioned partly or wholly within the cavity containing the tuneable clement that the Actuator serves to move or deform. In this case where the Actuator is at least partly inside the RF cavity it is necessary to minimise the RF field coupling to the conductive SMA material (wires, strips or sheets) of the Actuator. In order to prevent the SMA material from coupling strongly to the RF field in the cavity one or more of the following approaches may be taken: for a straight-wire strip or sheet SMA actuator where the SMA material is very thin, e.g. SMA material thickness << (electric wavelength of cavity), then the SMA material may be located entirely on or within the electric wall of the cavity (or simply parallel to the electric wall for mode TE,), or alternatively, the line or plane of the SMA material should be positioned orthogonal to and symmetrical to the magnetic walls of the cavity; where the SMA material or the SMA material and its conductive electrical connections (e.g. wires to an external SMA-actuator controller) deviate from a straight line within the cavity then they should be constrained to lie in a plane and that plane positioned orthogonal to and symmetrical to the magnetic walls of the cavity; further isolation of the SMA material and connecting wires thereto from the RF field may be achieved by sandwiching the planar arrangement of SMA material and connecting wires between two thin low RF-loss glass wafers held parallel to the electric field of the cavity, which effectively "suck-in" the surrounding RF field greatly reducing its amplitude in the vicinity of the Actuator structure. These glass wafers may be arranged not to touch the static or moving parts of the Actuator, but also may advantageously be used as support elements for the Actuator structure and even as the primary mechanical static portions of the Actuator; the SMA element(s) of the Actuator may also be electrically screened from the RF fields by partially or wholly surrounding them with conductive surfaces preferably metal or metalised plastic.

A tuneable filter that is to act as a phase-shifter has a nominally constant amplitude and linear phase response across its passband, and when tuned it is predominantly the magnitude of phase-shift at each frequency within the passband that changes, not the centre frequency or edges of the passband. Such a tunable phase-shifter filter consists of one cavity or a plurality of coupled cavities each containing one more movable elements.

In its simplest form a tuneable phase-shifter filter consists of a cavity in the form of a section of waveguide with conductive walls, open at one end and closed at the other, the open end serving as both the input-port and the output port, i.e. the I/O port. Within the cavity a moveable or deformable element, the tuning clement, is constrained to at least in part move along the waveguide in a direction towards and away from the PO port, with the movement or deformation caused by an Actuator, situated within the cavity or external to it, as described above for general tuneable filters of the present invention. The tuning element itself forms an electromagnetic discontinuity in the waveguide which thus reflects some of the RF energy back to the FO port. Ideally the tuning clement reflects all of the incident RF energy and at least a portion of it may preferably take the form of a plane conductive sheet or plate or conductive plated surface of a plane insulator almost filling the cross-section of the waveguide but preferably without touching it, and preferably without making electrical contact with the electrically conductive waveguide walls, movably supported so as to allow it to travel along the direction of the waveguide towards and away from the I/O port. Alternatively the tuning element may consist of a shaped resonator with a broad resonance across the passband of the phase shifter, made out of metal or a printed conductive pattern on a dielectric substrate. In operation RF energy propagates down the waveguide (e.g. in TE10 eigenmode) from the input port, is reflected back from the moveable element, and then exits the waveguide at the output port, the phase of the output wave relative to the input wave being directly proportional to twice the length of waveguide extending from the 1/0 port to the current position of the moveable tuning element. Because of the reflective nature of this tunable phase-shifter configuration it has the advantageous property that the amount of phase difference dphi produced by moving the moveable element a distance x is: dphi = 4rtx/L radians where I, is the wavelength in the medium of propagation within the waveguide of the wave being phase shifted. The extra factor of 2 achieved by the reflection (rather than pass-through) of the wave thus requires only half of the movement of the moveable element otherwise needed for the same amount of phase shift change, and this can simplify and/or lower the cost of the Actuator provided to move it. The RF field behind the moveable tuning element (i.e. on the opposite side of it to the I/O port) can be made small by suitable design of the tuning element (primarily by making it a highly efficient reflector) and this low RF field makes it relatively unproblematic to site the Actuator directly behind the moveable tuning element and within the cavity. In this case it is still preferable to follow the rules set out above for minimising interaction between in-cavity Actuators and RF field. Alternatively the Actuator may be sited within the thickness of or outside of the cavity wall opposite the I/O port (or indeed outside any of the adjacent side walls) when again the low RF field within this portion of the cavity minimises RF leakage issues around any moving parts passing through the cavity walls, which can be reduced further by the introduction of in-line RF chokes again as described above.

The phase-shifter as described above advantageously can be modified to reduce the required movement of the moveable element to achieve a given phase shift, by partially filling the cavity with dielectric. For example by placing glass wafers or other high dielectric constant material on the inside walls of the cavity it is possible reduce the effective wavelength of propagation within the cavity, whereupon a given change in phase shift is produced with a reduced movement of the moveable tuning clement.

In another aspect of the invention the tunable phase shifter filter comprises not one but two co-moving tuning elements separated by a distance in along the waveguide, where in is approximately half a wavelength of propagation in the cavity at the mid-range frequency of the phase shifter; the optimal separation in differs from an exact half wavelength due to the reactive conductance of the tuning elements, as well as the other structures within the cavity, primarily the Actuator or Actuator coupling mechanics that link an external Actuator to the moveable member. The beneficial effect of the second tuning element is an increase in bandwidth of the tuneable phase-shifter and an increase in reflectivity achieved and a reduction of RF losses. The two tuning elements may be mechanically joined by a stiff strut attached between them, which is preferably made of low loss dielectric, e.g. a glass wafer. In a preferred embodiment of this aspect of the invention, the Actuator used to move the moveable elements is sited inside the cavity in the gap between them, and as described above the conducting SMA material of and to the Actuator are held in the electric wall in the cavity to minimise coupling to the RF field. The two tuning elements may be identical or be made to differ so that they introduce reactances of different sign, thus providing the possibility to control the dispersion of the phase shift, or otherwise the linearity of the introduced time delay over frequency within the passband, or alternatively, achieving more compact design with reduced distance between the tuning elements.

Where a pair of tuning elements is used in any of these phase-shifter variants, then they may advantageously be mounted sandwiched between glass wafers with elements etched on both faces of the copper-plated glass wafer providing stable and well defined electrical distance between them and at the same time achieving economical design.

The tuning elements in each and all of the above aspects of the tunable phase shifter can take the form of conductive rectangles, conductive squares, conductive rings or conductive crosses, each of which has its own advantages and shortcomings. Selection of the optimal configuration of the tuning element is linked to the operating / dominant mode of the phase shifter. The element that provides the maximum coupling to the operating mode combined with the lowest achievable insertion loss should be selected. Narrow band phase shifters may employ resonant elements while more wideband devices will benefit from using non-resonant elements providing only capacitive or only inductive response.

A further aspect of the invention is a tuneable phase-shifter constructed as a waveguide cavity as described in all variants of two tuning clement phase-shifter above with the difference that now both ends of the waveguide are open (i.e. there is now no dosed end). In this aspect one end of the waveguide cavity acts as the input-port and the other end acts as the output port. The reflections back to the input-port of the two tuning elements are now arranged to cancel each other at the input-port to minimize the in-band return loss. The degree of coupling between the tuning elements will define the width of the passband, and consequently the amount of phase-shift in-band. Moving them simultaneously along the waveguide will not be useful in this configuration. Instead an Actuator is used to controllably change the distance between them which controllably changes their coupling, and each moveable element will be independently tuned by an Actuator (one per moveable element) to keep the elements tuned to the same central frequency. Thus this configuration will require at least three Actuators. In this through-waveguide phase-shifter configuration (as opposed to reflective waveguide phase-shifter configuration) the two tuning elements are optimally separated by a distance m along the waveguide, where in is approximately one quarter of a wavelength of propagation in the cavity at the mid-range frequency of the phase shifter; the optimal separation 111 differs from an exact quarter wavelength due to the reactive conductance of the tuning elements, as well as the other structures within the cavity, primarily the Actuator or Actuator coupling mechanics that link an external Actuator to the moveable member.

A phase shifter can be formed by two orthogonal transmission lines (Line V and Line H) supporting waves of orthogonal polarisations propagating in a direction P. The two lines may each for example be formed by pairs of spaced parallel conductors. A sliding plate placed orthogonal to the direction of propagation P and within the space between the four conductors forming the transmission lines contains a resonating structure formed by a metal structure layout on the plate surface resonating at the frequency of operation, to facilitate the reflection of an incoming wave. These metal structures are designed to resonate at the operating frequency; for example -conductive strips forming dipoles may be used, one dipole in each of the two orthogonal directions. The plate thus contains two types of structures -each designed to interact with the wave of corresponding polarization. This configuration of phase shifter provides dual polarized operation with identical phase shift introduced for Vertical and Horizontal polarizations supported by Lines V and H respectively.

A phase shifter for independent control of the two orthogonal polarizations is formed by two orthogonal transmission lines (Line V and Line H) supporting waves of orthogonal polarisations propagating in a direction P. Two plates orthogonal to each other and lying parallel to the direction of propagation P arc placed between the two transmission lines. One plate is orthogonal to the walls of line V and the other orthogonal to line H. A resonating structure designed to interact with one of the waves of each polarization is placed on each plate, one for each polarisation. One structure on one plate interacts with the wave supported by Line V, and the other structure on the other plate interacts with the wave supported by Line H. Each plate has independent freedom of movement in the direction of propagation P, and can be moved independently of the other with the help of dedicated slot in one plate that allows the other plate to move within it (in the slot) without mechanical interaction. A slot can also be placed in both pates to achieve the same end. Each plate is attached to a separate Actuator capable of moving the plate far enough to achieve the desired range of phase-shift of the waves.

So in one aspect of the present invention a tuneable RF filter comprises one or more resonant or reflective elements positioned in a waveguide with conductive walls and the one or more resonant or reflective elements are caused to move axially along the waveguide each by an Actuator. In a particular embodiment the waveguide conductive walls are formed from alternate metal and dielectric layers with adjacent metal layers joined together by rectangular arrays of conductive vias through the dielectric layers the rectangular arrays forming the walls of the waveguide whose axis is orthogonal to the metal and dielectric layers, and the waveguide cavity is formed by the removal of the dielectric and metal layers within and between the waveguide walls. In a different embodiment the waveguide conductive walls are constructed of conductive metal or conductively coated insulating material such as polymer, by, for example, metallising the polymer. In a preferred embodiment the one or more resonant or reflective elements are constructed so as to reflect as perfectly as practically possible all of the RF energy incident at one end of the waveguide back to that same end of the wavcguide with a phase directly proportional to the axial position of the moveable elements along the waveguide thus providing a single-port reflective tuneable phase-shifting filter. Preferably in this embodiment the length of the waveguide is at least half the wavelength within the waveguide of the waves of interest so that the reflected wave may be delayed by any phase angle between 0 and 360deg, allowing, for example, the construction of a phased-array antenna with an array of such phase-shifters. In another preferred embodiment, the length of the waveguide is a multiple (greater than 0.5, and quite possibly >5 or >10 or even more)) of the wavelength within the waveguide of the waves of interest, so that the reflected wave may be delayed by a time anywhere between 0 and the time taken to traverse the waveguide in both directions, which may advantageously be many cycle-times of the wave, allowing, for example the construction of a true-time-delay-array antenna, with greater bandwidth than an otherwise similar phased-array antenna. In another preferred embodiment two resonant or reflective elements are constructed so as to reflect as little as practically possible of the RF energy incident at one end of the waveguide back to that same end of the waveguide such that nearly all of the RF energy emerges from the other end of the waveguide with a phase directly proportional to the axial positions of the moveable elements along the waveguide and wherein a second Actuator is used to control the axial separation of the two resonant or reflective elements to optimise the input return loss with operating frequency thus providing a dual-port tuneable phase-shifting filter. In a further aspect of this invention two separate sets of one or more resonant elements are positioned in the waveguide, each set independently of the other moveable axially along the waveguide by independently controllable Actuators, and each set of resonant elements is responsive to only one of two different polarisations of waves incident on one end of the waveguide, for plane polarisation waves the different polarisations being orthogonal to each other, and for circular polarisation the different polarisations being of opposite sign.

Most generally: In one aspect of the invention a phase or frequency tuneable device (hereinafter Device A) comprises an RF cavity exploiting the thermo-mechanical properties of SMA material in the shape of wires or ribbons or sheets so arranged to form an Actuator applied in such a way as to achieve controllable deformation or controllable movement of the walls of the RF cavity, or controllable movement or controllable deformation of additional electromagnetic structures in the vicinity of or inside the RF cavity, so as to affect the electric and/or magnetic components of one or several of the eigenmodes of electromagnetic field supported by the RF cavity.

In a further aspect of the invention an RF tuneable filter device (hereinafter Device B) comprises two or more phase or frequency tuneable Devices A as just described wherein these two or more Devices A are each electromagnetically coupled to at least one other of the plurality of such devices.

In a further aspect of the invention an RF tuneable filter Device B as just described has at least one of the electromagnetic couplings between Devices A in the form of an iris penetrating the solid walls or ground planes separating the phase or frequency tuneable devices or by an iris formed by a gap in a wall of conductive vias separating those devices.

In a further aspect of the invention an RF tuneable filter Device B has at least one of the electromagnetic couplings between Devices A formed by the provision of additional non-grounded conductive tracks formed (e.g. printed) on an insulating layer itself formed on the inside or outside of one or both of the ground planes sandwiching the cavities to be coupled, and wherein the conductive tracks protrude into both of the adjacent cavities of the Devices A either without electrical connection to anything else or with both ends grounded.

In a further aspect of the invention an RF tuneable filter Device B has at least one of the electromagnetic couplings between Devices A formed by non-grounded cross-coupling wires protruding into both of the cavities of the adjacent Devices A through an iris either without electrical connection to anything else or with both ends grounded.

In a further aspect of the invention an RF tuneable filter Device B of any of the variants described above has at least one of the electromagnetic couplings between RF cavities of the Devices A tuneable by a tuning device comprising SMA material in the shape of wires or ribbons or sheets applied in such a way as to achieve controllable deformation or controllable movement of a conductive or dielectric tuning element in the vicinity of the electromagnetic coupling.

In a further aspect of the invention an RE tuneable filter device as in any of Device A or Device B variants described above comprises one or a plurality of stages, the filter either being of the low-pass, band-pass, band-stop, high-pass or phase-shifting configuration and further comprising two or more spaced conductive ground planes with joining walls connecting between the conductive planes and/or conductive vias positioned between the conductive ground planes, having inside between the ground planes one or a plurality of separate RF cavities separated by solid conductive partitions and/or by a plurality of conductive vias positioned between the conductive planes and in each of those cavities is zero, one or a plurality of resonators or electromagnetic reflectors, and where there is a plurality of cavities each cavity is electromagnetically coupled to at least one other cavity by an iris penetrating the solid walls or ground planes or by an iris formed by a gap in a wall of conductive vias between ground planes, and wherein one or more of the RF cavities has each one or more tuning elements penetrating into or wholly contained within the RF cavity and wherein each such tuning element is either wholly moveable or is deformable in such a way that the movement or deformation thereof changes the electromagnetic characteristics of the RF cavity so as to satisfy the tuneability requirement of the filter and wherein the movement or deformation of at least one of the tuning elements is caused by the expansion and contraction of one or more associated SMA structures each under the heating influence of a controlled electric current passing through said SMA structure and where each SMA structure is located outside of the RF cavity or within the walls of the RF cavity or located wholly within the RF cavity.

In all of the SMA actuated RF tuning and phase-shift devices described herein, there is a possibility of direct and unwanted interaction between the RF waves themselves and the SMA elements of the Actuator which are by their nature electrical conductors. In receiver applications this is unlikely to cause any problems for the SMA elements, &though they may act as unwanted absorbers of RE signals. However in transmission devices where the power levels can be high and the electric fields intense, it may become important to prevent unwanted heating of the SMA elements by the RF energy within the RF device being controlled, and this especially so when the Actuator is advantageously placed within the RF cavity. A convenient and effective way to minimise RF/SMA interaction, when the SMA element is in the form of thin wires, is to firstly, use insulated SMA wire, and secondly to use the insulated SMA wire in the form of tightly twisted-pairs as are familiar to those practised in the electronics signal processing art as an effective way to cancel interactions between fields and wires. A twisted-pair SMA insulated-wire element will contract upon heating and allow expansion upon cooling much as a single SMA wire will, but will provide approximately twice the pulling force, with little if any increase in cooling time constant. There is the added advantage that the heating current to such an SMA element may be provided entirely from one end -where an SMA element has one fixed and one moving end (very common) then at the fixed end current may be supplied up one strand and down the other, and all that is necessary at the moving end is to cornet the two strands to each other, and to nothing else. This eliminates the otherwise sometime difficult problem of creating a reliable current return from a moving component.

So in this aspect of the present invention any Actuator used near or within an RF environment, and especially within any of the tuneable RF devices described herein, is comprised of twisted-pair insulated SMA wire elements, with the length between successive twists at most half a wavelength of the RF energy of concern, and preferably much smaller than half such a wavelength.

More generally it may often be useful to use insulated SMA wire for the SMA elements of any SMA actuators used to tune the RF devices described herein. And to avoid other interactions with RF currents flowing through the conductive structures of the RF devices being tuned, it is preferable in all cases to provide a return path for any SMA element heating current that is separate from the conductors of the RF energy.

DRAWINGS

We will now describe aspects of the present invention with respect to the drawings.

Brief Description of Drawings:

Fig.1 illustrates one arrangement of a tuning element of the present invention relative to a resonator in a conventional solid-wall cavity.

Fig.2 illustrates one arrangement of a tuning element of the present invention relative to a resonator in a cavity constructed between a pair of ground planes.

Fig.3 shows an arrangement according to the present invention of two coupled and tuned resonators sandwiched between ground planes (one plane removed for clarity).

Fig.4 illustrates all of the components needed for a complete but simple tuneable two-resonator filter with I/O ports.

Fig.5 illustrates an alternative arrangement of the components of the tuneable filter of Fig.4.

Fig.6 (A, B, C, D, E) illustrates a 3D folded tuneable six resonator filter with three ground planes.

Fig.7(A, B) illustrates an integral tuner, Actuator and resonator.

Fig.8(A, B, C, D, E) illustrates an SMA tuneable-phase reflective waveguide phase-shifter filter.

Fig.9 illustrates a two-Actuator tuneable through-waveguide phase-shifter filter. (There is no Fig.10) Fig.11 shows an alternative SMA integrated capacitive tuning element.

Fig.12 illustrates a twisting-mode SMA magnetic 110 coupling mode tuning element. Fig. 13 illustrates a bending mode SMA tuned resonator.

Fig,14(A) illustrates an alternative Faraday cage bending mode SMA tuned resonator. Fig.15 shows a form of waveguide-phase-shifter with phase adjusted by an Actuator.

Fig.16 shows a modified form of waveguide hase-shifter capable of independently varying the phase of each of two orthogonal polarisations, and capable of modification to independently tune each of two opposite circular polarisations, Fig.17 shows a phased-array antenna comprising an array of SMA-tuneable phase-shifters with an offset feed and a schematic beam produced by the array.

Detailed Description of Drawings:

Fig.1 shows a schematic section of a conventional solid wall cavity, with two opposing sections (the rest is not shown, for clarity) of solid conductive wall I and 2 parallel to each other containing in between them a resonator 3 which is galvanically grounded at one end to wall 2 and unconnected at its other end, which instead has a glass wafer 4 attached to its surface. Also not shown (again for clarity) are the remaining conductive walls of the cavity that define its shape and volume. A tuning element 5 of the present invention nominally parallel to wafer 4 penetrates wall I through an aperture in that wall and is positioned a small precise orthogonal distance from glass wafer 4, and is slidably mounted such that it can move in and out of the cavity formed between walls 1 and 2. Its movement is in turn controlled by Actuator 6 which is shown only schematically, and is mechanically attached to Actuator 6 by link-pin 7, so that when Actuator 6 moves the tuning element 5 may be positioned at a range of distances along the end of resonator 3. This has the effect of modifying the capacitance (primarily) at the end of resonator 3 which in turn changes its resonant frequency, providing a tuning function. Actuator 6 is mechanically attached (not shown) to the outside walls of the cavity. In this example the tuning element 5 is made of conductive material and extends through the cavity wall 1 to the outside and provides an unwanted potential leakage path for RF energy from inside the cavity. Such leakage is prevented in this example by the integral RF choke built into tuning element 5 in the form of a series of wide (capacitive) and narrow (inductive) sections of the tuning clement, formed by cutting notches one of which is shown at 8 into either side of the element and spaced along the element in the direction along the tuning element. A further pair of notches similar to those visible at 8 are cut into the portion of tuning element 5 where it penetrates the cavity wall 1 and which are thus not visible in this view. As described previously, the glass wafer 4 could advantageously be replaced by a corundum coating on either of the two adjacent faces (i.e. resonator or tuning element) to act as a very high quality high dielectric-constant dielectric between them.

Fig.2 shows a schematic section of a cavity constructed between two parallel conductive ground planes 10 and 11, only sections of which are shown for clarity) and which are electrically and mechanically connected to each other by a number of conductive vias 9 most of which are not shown, for clarity. The size and volume of the cavity are defined not only by the ground planes 10 and 11 but also by "walls" made up of suitably spaced conductive vias such as 9 but these additional cavity "walls" are not shown in this figure, for clarity. Contained in between them is a resonator 3 which is galvanically grounded at one end to a pair of vias 9 and unconnected at its other end, which instead has a glass wafer 4 attached to its surface. A tuning element 5 of the present invention nominally parallel to wafer 4 penetrates into the cavity through an iris formed by an adjacent pair of vias 96 the positioning and separation of which are chosen to minimise RF energy leakage from the cavity along the direction of the tuning element 5. The tuning element 5 is positioned a small precise orthogonal distance from glass wafer 4, and is slidably mounted such that it can move in and out of the cavity formed between ground planes 10 and II. Its movement is in turn controlled by Actuator 6 which is shown only schematically, and is mechanically attached to Actuator 6 by link-pin 7, so that when Actuator 6 moves the tuning element 5 may be positioned at a range of distances along the end of resonator 3. This has the effect of modifying the capacitance (primarily) at the end of resonator 3 which in turn changes its resonant frequency, providing a tuning function. Actuator 6 is mechanically attached (not shown) to the outside of one of the ground planes. In this example the tuning element 5 is made of conductive material and extends outside the cavity through the iris formed by two of the vias 96 and could provide an unwanted potential leakage path for RF energy from inside the cavity. Such leakage is prevented in this example by the integral RF choke built into tuning element 5 as can be seen more clearly in the tuning pin drawing in Fig.l. However, clearly shown in Fig.3 is a conductive plate 801 grounded in this example by the two vias 96, which is arranged parallel to and very close to the surface of tuning clement 5 to provide strong capacitive decoupling to the region in and around the notches forming the integral RF choke. Such grounded capacitive elements (i.e. like 801) are to be understood to be similarly positioned over the notched RF choke sections of all the tuning elements in all of the figures, but are mostly not shown for clarity (i.e. to allow visibility of components and structures that would otherwise be hidden by the presence of these capacitive elements. They form an integral part of the in-line RF chokes.

Fig.3 shows two coupled resonators 3 and 31 grounded at one end by vias 9 and sandwiched between two parallel ground planes 10 and 11 as before in Fig.2, except that ground plane 10 has been removed in Fig.3 to reveal the structures between them. The two resonators have glass wafers 4 and 41 covering part of one face near the end opposite the grounded end, and the resonators are tuned by moveable grounded tuning elements 5 and 51 which arc in turn moved by Actuators 6 and 61 which are shown only schematically. The two resonators are electromagnetically separated from each other by a set of closely spaced vias 9 lying between them and connecting at each end to the ground planes 10 and 11, and this line of vias effectively forms one "wall" of each of the two cavities in which sit the resonators 3 and 31. The remaining walls of these cavities which arc similarly constructed of lines of closely spaced vias are not shown, for clarity. However, near the tuned end of the resonators there is a carefully shaped and positioned and sized gap in the cavity-separating wall of vias between the vias 91 and 92 and at that location this gap functions as the coupling iris which electromagnetically couples the two resonators 3 and 31. The notches some of which are indicated at 81 forming the integral RF chokes in the tuning element 51 can be clearly seen in this drawing, although only one notch at 8 is visible in tuning element 5 because the figure shows the capacitive cover plate 801 grounded by the vias 96 which normally covers all such notches in such integral RF chokes and is an integral part of the RF choke structure. Other cover plates like 801 have been removed in the drawings to more clearly show the structures beneath but it is to be understood that some conductive structure serving the same capacitive function would be expected to be present in all such integral RI chokes.

Fig.4 is a further development of the structure shown in Fig.3 and is now in this drawing complete enough to form a fully functional tuned filter. The additional elements will now be described. The coupling iris between the two resonators 3 and 31 previously (in Fig.3) formed between two vias 91 and 92 has now become a tuned coupling and is formed between via 92 and conductive tuning element 52 which is moved towards and away from via 92 by Actuator 62 shown schematically only. Again there is an integral RF choke along the stem of 52 formed by a series of notches, and a grounded capacitive cover plate over these (not shown) as described above. So while the two resonators 3 and 31 may be independently tuned by Actuators 6 and 61, the coupling between them may also be independently tuned as well, by Actuator 62, the action of which is to open and close the gap in the electromagnetic wall between the resonators, as tuning element 52 moves. An input port to the filter is formed by a stepped cylinder 111 the function of which is to convert the impedance at the input end 121 (e.g. typically 50ohm if this was a coaxial connection) to the impedance of the resonator 31 to which impedance converter 111 is electrically bonded (e.g. soldered). The overall function of this subassembly is to connect with low return loss an input signal into the cavity containing resonator 31. Similarly, an output port is provided at the end 120 of a stepped cylinder impedance converter 110 electrically connected to resonator 3 at the other end. Typically the output port 120 might also be matched to a coaxial connector, e.g. at 50ohm impedance. These two input/output ports (I/O ports) are each separately tuned by grounded conductive tuning element 53 (for the input port at 121) and grounded conductive tuning element 54 (for the output port at 120) and the tuning is accomplished by moving these tuning elements towards and away from their respective stepped cylindrical impedance converters, the movement being produced by Actuators 63 and 64. These tuning elements 53 and 54 operate in magnetic mode rather than electric mode, and are grounded to the inside of the cavity by elements not shown for clarity.

Fig.5 illustrates an alternative arrangement of the components of the two-resonator tuneable filter shown in Fig.4. Here one of the resonators, 3, has been flipped through 180 degrees end to end so that it still lies parallel to the other resonator 31 but has it's grounded end at the opposite side of the ground plane to the other resonator. It's I/O port 120 and tuning elements 5 and 54 (and associated components) have all moved with it, so that functionally this layout is more or less identical to that in Fig.4. However, when putting together a number of filter sections to make a more complex design, this ability to flip resonator cavities gives great flexibility, particular when building triple (or more) ground plane 3D filters.

Fig.6A illustrates a 3D folded tuneable filter with three ground planes 10, 11,12, six resonators and with I/O ports at 121. This is effectively a development of the complete tuneable filter shown in Fig.4 and Fig.5, now with six resonators (three between ground planes 10, 11 and three more between ground planes 11, 12) and additional inter-cavity couplings between each pair of cavities adjacent to each other on opposite sides of the central ground plane 11. The following parts of Fig. 6 show all this in more detail.

In Fig.6B the top ground plane 10 has been removed to show the top layer internals, where three resonators 3, 31, 32 can be seen each situated in their own cavities defined by closely spaced walls of conductive vias connecting between ground planes 10, 11 not all of which are shown, for clarity. Each resonator 3, 31, 32 is tuned respectively by tuning elements 5, 51, 52 themselves made moveable by Actuators 6, 61, 62. The tuning elements are RF isolated from their Actuators by integral RF chokes implemented as a sequence of wide and narrow sections along the length of the elements and these sections are capacitively coupled to ground by grounding sections not all of which are shown for clarity. An I/O port 121 can be seen to couple into the cavity containing resonator 3 and this coupling is magnetically tuned by tuning clement 56 moved by Actuator 66. The coupling between the cavities of resonators 3, 3] is tuned by tuning element 57 moved by Actuator 67 and that between the cavities of resonators 31, 32 by tuning element 58 moved by Actuator 68. The cavity of resonator 32 is coupled through an aperture or iris in ground plane 11 (not visible in this view), to the cavity beneath it between ground planes II, 12 and this coupling is tuned by tuning element 59 (only the far end of which is visible in this drawing where it is connected to its associated Actuator 69). This iris coupling represents the sequential path through the six-resonator filter. However there are additional couplings through the central ground plane]] between the other two pairs of cavities which lie adjacent to each other on opposite sides of central ground plane 11, though these additional couplings are not visible in this drawing. These additional throughground-plane-couplings are also each independently tuned by a further pair of tuning elements moved each by their own Actuators, again not shown in this drawing for clarity.

Fig.6C is a close-up view of the through-plane iris 200 coupling the cavities of resonator 32 and 33. Resonator 32 which lies between planes 10, 11 as can be seen in Fig. 6B has been removed in this drawing to reveal the coupling iris 200 beneath it, which coupling can now be seen to be tuned by grounded conductive tuning element 59 (also beneath resonator 32) moved by Actuator 69. Resonator 31 which is parallel and adjacent to (removed in the drawing) resonator 32 is shown in the drawing. The iris-end of tuning element 59 has a tab or ridge 259 on it which is narrower than the iris slot 200 so that when clement 59 partially covers iris 200 it forms a ridge-loaded waveguide between the cavities on either side of plane 11 which assists coupling and tuneability. A ridge-loaded waveguide section is therefore formed inside or in the vicinity of the coupling iris 200 (i.e. a waveguide loaded with a ridge in the middle) and this structure has the lowest cut-off frequency. which is strongly dependent on the ridge and the shape of the waveguide, and in particular on the gap between the ridge tip and the opposite wall of the coupling waveguide. Even when the ridge does not fill the entire thickness of the iris 200 it will strongly affect the coupling value. A possible variant of the structure shown in Fig.6C has a coupling pin with a thicker tip protruding through the entire thickness of the iris 200. In this view the resonator 33 in the cavity below plane 11 is mostly hidden from view by ground plane 11 although a portion of it closest to iris 200 is visible through the iris. Just visible to the left of iris 200 is the capacitive grounding plate 802 of the tuning clement 52 which is used to tune resonator 32. Also now clearly visible is tuning element 58 moved by Actuator 68 which tunes the coupling iris between the cavities of resonators 31 and 32 (latter not shown for clarity).

Fig.6D is another close up of this through-ground-plane iris 200 where the centre ground-plane 11 has now also been removed to reveal the structures beneath. The iris 200 is shown in outline directly beneath the tip 259 of iris coupling tuning element 59. Now also visible is tuning element 53 (moved by Actuator 63) which in conjunction with dielectric element 43 tunes resonator 33, several conductive vial 9, as well as Actuator 62 which moves tuning element 52 which tunes resonator 32.

Fig.6E shows a variant on the coupling tuning element of Fig.6C, where a true ridged waveguide between the two coupled cavities is formed. Tuning element 59 now has an extra thickened section 2591 on the tab 259. Element 59 moves in the direction shown by the arrow 001 over the surface of ground plane 11 so that the thickened tab 259 now fills the full thickness of the iris 200 in ground plane 11 so that a true ridged waveguide is formed. A copy of 59 is shown at 59A to clearly reveal the shape of the modified tab end 259, 2591.

In all of the drawings of tuned filters so far (i.e. Fig.l -Fig.6D) the Actuators have been sited either outside of the RF cavities or in some cases merged with them, and in general could be any suitable type of actuator, though as aspects of the present invention, as mentioned above, they are any sort of SMA actuator, suitably configured to give enough stroke with adequate load-force capability. In many cases a double-bowstring actuator will serve this purpose well as its stroke can be tailored within wide limits even in a compact actuator, as the forces required for tuning these tuned filters are small typically <1 gram, and even a 25micron diameter SMA wire can pull nearly 15 gram and so quite high leverage can be applied to increase the stroke above that available directly from the contraction of a straight wire typically 3-4%, but sometimes more, of its length). So it should be understood that where these Figs. label components as "Actuators" (e.g. 6, 61, 62, 66, 67, 68, 69 in Fig.6B) it is intended to mean that a suitably specified SMA actuator should be used for that component, as per the definition of Actuator above.

Fig.7 is a development of the aspect of the invention shown in Fig.4 with which Fig.7 should be compared. The standalone Actuator 6 of Fig.4 used to tune resonator 3 has now been replaced with a completely integral actuator built in and around resonator 3 in Fig.7. So in this figure can be seen an SMA wire 171 running the length of resonator 3 and in this case housed inside a groove in resonator 3 which groove is lined with electrically insulating material, preferably grown on the surface of 3 which if of aluminium may be aluminium oxide A1,03 (in which case a further cost saving and simplification can be achieved by simultaneously growing a similar very thin insulating dielectric layer of A1,0, on the top surface of the end of the resonator to replace the separate dielectric element 4 which forms part of the tuning structure). SMA wire 171 is mechanically anchored in an insulating member 170 positioned on the grounded base end of resonator 3 and is electrically terminated here to a wire (not shown) connecting it to a controller which supplies heating current to change the length of the SMA wire. The other end of SMA wire 171 is mechanically attached to grounded tuning element 5 which is moveably mounted so as to be able to slide over thin dielectric layer 4 (as before in Fig.4) along the direction of the length of the resonator 3. This end of the SMA wire may also optionally be electrically bonded to grounded tuning element 5 which then forms a return path without additional wires, for the SMA-wire heating-current. When the SMA wire 171 is heated by the controlled current and subsequently contracts, tuning element 5 is pulled in the direction towards the resonator's grounded base and in so doing more overlaps resonator 3 increasing the capacitance between these elements and thus tuning the resonator. Also attached to tuning element 5 is one end of a spring, a leaf spring 172 in this variant, whose other end is attached to the base plate ground plane 11 via some form of mechanical mounting, shown in this Fig. as pin 173. The spring force is arranged to oppose the pulling force of SMA wire 171 such that when the heating current to the SMA wire is reduced, and the SMA wire cools, spring 172 stretches the SMA wire back to its original (unheated) length, thus performing the return-stroke function of the actuator so formed. An alternative to return spring 172 is to add a second SMA wire capable of pulling 5 in the opposite direction to SMA wire 171. This may also be conveniently arranged to run along the length of resonator 3, but in this case one end of the wire is mechanically attached to base 11 (or 10) in the region of pin 173 (but in line with wire 171) and the other end to an insulating mechanical rod or strut or link extending from tuning element 5 above the length of resonator 3 to a point near to or above mount 170 at which point the second SMA wire is attached to the rod. In this way both SMA-wires can have similar lengths and be nearly co-located so taking up very little extra space, but may operate as a push-pull pair of actuator wires as is known in the art. The actual detailed configuration of the integral SMA actuator can of course take many forms known to those skilled in the art and the configuration shown here is not meant to be in any way limiting but merely indicative of what is possible. In this drawing tuning element 5 is grounded and covered by grounding plate 801 although it may also be arranged to be grounded by any other suitable means, to either of the adjacent ground planes of the filter (i.e. /0, //). One of the immediate advantages of this implementation of a tuning actuator may be seen to be that it is entirely enclosed within the RF cavity surrounding resonator 3 and takes up hardly any additional volume, and also requires no RF chokes or other countermeasures to reduce RF energy leakage along mechanical linking structures. It might also be expected to cost less to implement than a separate actuator structure.

Fig.7A shows a close-up view of the grounded end of resonator 3 from Fig.7, and illustrates the location of SMA wire 171 sited in groove 175 of the resonator 3 and mechanically terminated on insulated mount 170, and shows the electrical termination point 176 of the SMA wire. The moveable tuning element 5 can be seen at the opposite end of the resonator separated from it by dielectric layer 4 together the latter's grounding plate 801. Several conductive vias 9 are also visible but note that the ground planes 10, 11, 12 are not shown in this drawing.

Fig.7B shows a close-up view of the non-grounded end of resonator 3 from Fig.7 now looking from the underside (i.c from the direction of ground plane 11), and again illustrates the location of SMA wire 171 passing along a groove in the surface of resonator 3 and mechanically (and in this case electrically too) terminating in a conductive mounting point 177 connected to tuning element 5. The return spring /72 is clearly visible in this view attached at its free end to tuning element 5 at point 178 and at its fixed end to ground plane 10 (not shown) via post 173. In this view spring 172 is significantly extended and SMA-wire 171 significantly contracted (i.e. the SMA wire is hot) which causes tuning clement 5 to significantly overlap resonator 3 increasing its capacitive coupling to ground.

The SMA wire actuator integral with a resonator as illustrated in Figs.7, 7A, 7B, may of course be used in any place in a tuneable filter of the present invention where a tuneable resonator or other form of tuneable or moveable element is required. One disadvantage of this particular arrangement shown is that a straight-wire actuator configuration is used. While the length of a resonator may be sufficient to house enough length of SMA wire in this way to achieve the required range of tuning (i.e. sufficient actuation distance), there is no leverage between the moving end of the SMA-wire and the moveable element even though the force capability of even a 25micron SMA-wire is usually many times greater than that required to move such moveable tuning elements, and as a consequence, the power consumption (proportional to SMA-wire length) of this configuration of actuator will be higher than otherwise achievable with a suitably long lever (e.g. as maybe achieved with a bowstring or double bowstring actuator). So this particular representation of integral SMA-wire actuator is meant only to be illustrative of what can be achieved and in no way limiting to all of the other ways that such leverage may advantageously be incorporated in an integral SMA actuator, whereupon compactness, low cost, simplicity as well as low-power consumption may all be achieved simultaneously.

Fig.8 shows a tuneable filter where the phase is the primary parameter changed by tuning (a phase-shifter) which is one aspect of the present invention. There are three layers of metal 510, 520, 530 each on top of a layer of dielectric 511, 521, 522 and these layers are all sandwiched together as shown in the Fig. The top layer of metal 510 can be seen to have an aperture in it of rectangular shape with rounded corners, exposing a portion of the dielectric 511. The other layers of metal are of similar shape. The top metal layer 510 is joined to the middle metal layer 520 by a rectangular array of closely spaced conductive vias 9 piercing the dielectric layer 511, two such vias being labelled 9. The diameter and spacing of the vias are chosen appropriately so as to form a waveguide for the RF frequency of interest, as is known in the art. The second metal layer 520 is similarly joined to the next metal layer 530 by a further similar rectangular array of closely spaced conductive vias piercing the dielectric layer 521 thus extending the waveguide so formed. Each layer of dielectric 511, 521, 522 has a rectangular slot 519 cut through it somewhat smaller than the aperture in the metal layers in such a way as to minimize the impact to propagation conditions of the dominant operating mode of the waveguide. For example, a large slot aperture may eventually move the cutoff frequency upwards to the extent it reduces the operating frequency band. The aperture size is chosen to ensure that this does not happen. In practice this is defined by the dielectric parameters of the manifold substrate and those of the structures supporting the resonators, and may require an additional dielectric filler in front of the resonator to keep the cut-off frequency within desired limits. This dielectric filler would then become another dielectric layer atop element 512 and become part of the moving element of this filter. There are graphs of cutoff frequency for such structures available in the literature and known to those skilled in the art which may be used to determine the required dimensions. In this slot in the fixed dielectric layers 511, 521, 531, is a moveable element including a resonator 512 supported by a dielectric constant support 513 (which may be a low-dielectric constant material), which moves in a direction orthogonal to the plane of the metal layers. In the aspect of the invention shown in Figs.8 the resonator is a conductive flat metal element in the shape of a capital letter I' (more clearly seen in Fig.8A), but other useful shapes are possible and known in the art. For example, the 'I' shape of elements shown may advantageously be rotated through 90deg in the plane of its thickness and suitably re-scaled to extend to the limits of the support 513 so that the stem of the points along the height of the waveguide rather than its width. The moveable element is caused to move by an Actuator 561 a small portion of which is visible beneath the bottom dielectric layer 531. In operation the top aperture in metal layer 510 is a waveguide I/O port and RF energy entering the port travels down the waveguide in both air (in the central cavity 519) and dielectric (between the cavity walls and the walls of conductive vias 9 surrounding the cavity), is reflected from the structures of the moving element (further described below) and returns to the 110 port with a phase proportional to the distance of resonator 512 from the I/O port entry defined by the metal layer 510. The output phase of the phase-shifter is thus controlled by the position of the moveable element which in turn is controlled by Actuator 561, which may in turn be controlled by electronic / digital commands from a controller.

Fig. 8A is a top view of the phase-shifter of Fig. 8 which now clearly shows the 'I' shaped resonator 512 supported by support 513, and also visible is the small clearance gap between these moveable parts and the surrounding dielectric layers 511, 521, 531. The top metal layer 510 with its round-cornered rectangular waveguide aperture cut through it is also clearly seen, as are the conductive vias 9 connecting it to the metal layer 520 below which form the walls of the waveguide.

Fig.8B is a cut away view of the phase-shifter where the dielectric layers 511, 521, 531 have been removed to reveal the walls of vias 9 connecting the metal layers 510, 520, 530 forming the waveguide. The resonator 512 on the moveable element support 573 is also just visible. In this version of the phase-shifter there are three layers of buried vias 9 rather than two and a fourth layer of metal on the bottom of dielectric layer 531, which lengthens the waveguide and allows for a greater range of travel of the moveable element while still remaining within the waveguide, accommodating greater values of phase shift.

Fig. 8C shows another cutaway view of the phase-shifter looking upwards from beneath, with all but the top layer of metal and vias removed, as well as the three dielectric layers removed, to reveal the moving element comprised of its support 513 and resonators, the second of which 514 can now be seen on the opposite side of 513 to where resonator 512 is positioned. This pair of resonators 512, 514 are spaced apart in the direction of movement by a fixed distance chosen to maximise the reflection of RF energy back to the I/O port, and this distance is equal to half the wavelength of operation of the phase-shifter corrected for the reactance of the resonators. The Actuator 561 (which is supported by the rear of dielectric layer 531 not shown) is mechanically coupled to the moving element by a link 515 made of any suitable non-conductive material.

Fig.8D shows a cutaway view of a slightly simplified version of the phase-shifter described above in Fig.8 to Fig.8C, constructed by replacing the pair of resonators 512, 514 on the moveable element by a single conductive metal reflector or resonator, in which case the spacing support 513 is no longer required, and the Actuator 561 may then be coupled directly to the first and only reflector 512. in the drawing the resonator/reflector is shown as a self-supporting conductive (e.g. metal) 'I' shape, but this could be replaced by other shapes with the appropriate resonance and/or reflective properties, e.g. a flat rectangular conductive sheet filling the whole aperture through the dielectric in the waveguide except for a small clearance gap around the edges. An alternative construction would have the conductive metal resonator/reflector etched or plated onto a thin dielectric backing support material.

Fig.8E is a more detailed development of the type of phase-shifter sketched in Fig.8D where we have shown more of the conductive metal layers 510, 520, 530 and via waveguide walls 9 (with some cut away for clarity). The moveable resonator/reflector 512 is now directly mechanically connected to the moving member 568 of a double-bowstring SMA wire actuator comprised of base 567, SMA wires 562, 563 terminated mechanically and electrically to pins 564 fixed to base 567 at their ends, and half-looped around pins 565, 566 fixed to moving member 568. The base 568 is mechanically fixed to the body of the phase-shifter, e.g. to the lowest layer of dielectric, not shown in this drawing for clarity. When one of the SMA wires is heated enough it will shorten and pull 568 with it, after which heating the other SMA wire causing it to shorten and allowing the first to cool will pull 568 with it in the opposite direction, axially along the waveguide. In this particular configuration moving member 568 is guided by a slot in base 567. The SMA wires 562, 563 are positioned in the electric wall of the waveguide and will have minimum coupling to any RF field behind the resonator/reflector 512. It will be seen that the actuator has now been brought inside the waveguide. The small size and flat profile of such SMA wire actuators allows them to be safely placed inside RF cavities and waveguides so long as they lie in the plane of the electric wall and thus remain decoupled. Thus an alternative configuration of the phase-shifter in this drawing could have one of the SMA actuator wires on either side of the resonator/reflector 512 so long as these rules are adhered to. This makes for a more compact assembly. Another variant has the base 567 of the actuator extending (further left and right in the drawing) into and/or beyond the walls of conductive vias to allow longer SMA actuator wires and thus greater stroke to be achieved. It is only necessary to ensure that the SMA wires do not touch the grounded parts of the metalwork (vias or ground planes).

The more detailed description of better integrating an SMA actuator with a moveable element outlined in the description of Fig.8E can be applied to most or all of the other actuator configurations shown in the previous Figs. to make low-cost, compact and efficient tuneable filters of all of the varieties described.

Fig.9 shows a different aspect of the present invention in the form of a phase-shifting filter similar in many ways to that of Fig.8 except that Fig.9 shows a through-waveguide phase-filter and not a reflective filter, where one end of the waveguide formed by the rectangular arrays of conductive vias 9 is an input port (say the top in Fig.9) and the other end (say the bottom in Fig.9) is the output port. As in Fig.8E the layers of dielectric in and around the conductive vias has been removed for clarity, and the metal layers 510, 520, 530, 540, 550 too have been cut away to show the internals as have some of the arrays of vias. Inside the cavity in the dielectric layers can now be seen two Actuators, illustrated here in non-limitative fashion as double bowstring actuators, the top one comprising two SMA wires 562, 563 in a bowstring configuration (for example, and not in any limiting way), a moveable element 569 connected mechanically to a top reflector/resonator element 512 which it can move axially along the waveguide relative to Actuator support structure 567. A second resonator/reflector element 5121 is mechanically connected to Actuator support 567 and this whole assembly of top Actuator and both reflector/resonator elements is in turn caused to move axially along the waveguide by a second Actuator below it in the figure, fixed to the phase-shifter body structure, for example to one of the dielectric layers of the stack. This second lower Actuator again shown for illustration only in this example has a pair of SMA wires 5621, 5631 in a bowstring configuration which move a moveable element 5681 which mechanically connects to the first Actuator above and causes it to move relative to the waveguide; its base 5671 is fixed mechanically to the phase-shifter body. The control wires (for heating the SMA wire) of the upper Actuator can be either flexible (to allow free movement of this Actuator) and constrained to the electric wall and led out of the sides of the waveguide though small apertures in the dielectric and between the walls of vial, or instead maybe led out to the lower Actuator with flexible leads (to allow free relative movement) and then carried to the outside alongside the lower Actuator's control wires, again through suitable small apertures in the dielectric walls. The purpose of the first Actuator is to maintain the correct spacing between elements 512, 5121 for minimum reflection to input port at the operating frequency at any time. So these two Actuators are now right inside the waveguide cavity where the RF energy of interest is flowing (in this case from top to bottom) and so as to interfere as little as possible with the RF, the plane of the SMA actuator wires and their external connections (not shown) is aligned with the electric wall in the cavity; to further enhance the decoupling of all of these wires, the Actuators arc each sandwiched between a pair of dielectric (e.g. glass) wafers 569, 569A for the top Actuator, and 5691, 5692 for the bottom Actuator, some of which have been cut away in the drawing to show the Actuator structure within, and these dielectric wafers effectively "suck in" the RF field near the wires and so minimise its interaction with them. Now the two reflector/resonator elements 512, 5121 are no longer identical and their shapes and separation are chosen to minimise the reflection of RF energy back to the input port whilst achieving the required phase-shift at the output port at the operating frequency. In operation the upper Actuator adjusts the axial separation of the reflector/resonators 512, 5121 and the lower Actuator moves them both bodily along the waveguide axially. While the Fig. Shows T-shaped resonator/reflectors, these may equally well be other shapes such as circular or elliptical rings, or cross-shaped elements; in fact any shape with the correct reflective and phase-shifting properties. A further refinement (not shown in this drawing for clarity) is the provision of additional Actuators and tuning elements (which could take the form of moveable capacitive elements, or inductive elements as described elsewhere above) for each of the reflector/resonators 512, 5121 to minimise reflections to input port right across the frequency band of interest, each of these being co-moving with their respective resonator/reflector element. The very low mass and compactness of these SMA-wire actuators makes such a device quite practical. Thus a very compact, verylow-RF-loss and low-cost through-waveguide tuneable phase-shifting filter may be provided in this way, which is simply not possible with conventional tuning elements and actuators such as electric motors which could not be placed inside the waveguide, and with no moving parts penetrating the waveguide walls and thus providing no leakage paths for RF energy. Such multiply tuned through waveguide phase-shifters have particular application where extremely low loss across a variable frequency waveband is required and some examples where they may be useful include industrial microwave ovens, timber driers, and crude-oil warming equipment, and indeed anywhere where tuning speed is secondary but cost and low RF loss arc paramount.

(There is no Fig.10) Fig.11 illustrates another aspect of the invention where the tuning elements, previously operable by moving relative to their target tuned element, now instead deform rather than move as a rigid body, the deformation being maximised in the region close to the tuned clement. The advantages of deformation instead of movement includes no sliding and so no friction, simplicity, potentially use of shorter SMA wire actuators which result in lower cost and reduced drive power, the elimination of the need for a separate return spring for the actuator (the deformed element itself provides that function), extreme compactness, highest reliability, and the ability to place the entire actuated tuning element right inside the waveguide to eliminate RF leakage to the outside. In Fig.11 we see the same resonator 31 and capacitive tuning element 51 as was previously illustrated in Fig.4 where it was moved by a separate Actuator 61 that had to be isolated from the RF in the cavity by an integral RF choke structure comprising the slots 81 in Fig.4. However, now in Fig.11 51 is a thin, conductive, elastic flexible strip mechanically mounted and grounded at one end by for example a pair of vias to a ground plane (not shown), with a free end 518 which is turned up in Fig.11 for several purposes: first it stiffens the thin strip laterally, second it provides a mechanical anchor point for an SMA-wire 178 in the centre at 179, third it can provide an electrical termination for the SMA wire in which case 179 could conveniently be a crimp formed out of the material of element 51, and fourth, importantly an out-of-plane attachment point for that SMA-wire to provide sufficient leverage to allow the SMA wire 178 when heated and controllably contracted to pull the end of the strip 51 out of the plane of its base mounting and so bend up the strip away from the dielectric 41 between it and the resonator 31, in so doing changing the capacitance between 51 and 31 significantly and thus tuning the resonator 31. The other end of SMA wire 178 is mechanically terminated in an insulating mount 177 and controlled heating current is fed into end 176 by a control wire (not shown), the return current conveniently run through the grounded end of the wire at 179. Only a short length of SMA wire 178 is needed to produce significant bending. The strip 51 can be very thin, just a few multiples of skin-effect-depth (e.g. -Ium in copper at 5GHz) at operating frequency being adequate to produce insignificant losses, and the material of strip 51 can be chosen for its mechanical properties alone (e.g. phosphor bronze, or a polymer) if it is plated or coated with a suitable conductive surface e.g. silver. So long as the strip is adequately elastic that it returns to a flat shape (and produces adequate return force to re-stretch the SMA-wire) when the SMA-wire is unheated its mechanical properties are not critical, though thermal expansion coefficient might be chosen to cancel thermal expansion coefficient effects of the rest of the tuned cavity. Note that although in this illustration the deformation of RF element5l is produced directly by a section of SMA wire/78, the same effect with somewhat more complexity may be produced by substituting an Actuator in place of wire 178, for example by an SMA-stepper-actuator, to provide improved long-term-position stability, plus other benefits as described above. Similar substitution of SMA-wirc by stepper-actuator considerations apply to the deformable structures with integral SMA wires described in Figs. 12/13/14/14A, and are included herein.

Fig.12 is another example of the deformation-tuning technique described in Fig.11. Fig.12 shows an I/O port tuning clement 53 first seen in Fig.4 where it was moved longitudinally towards and away from the T/0 port components 111, 121 by an external Actuator 63 and RF isolation was performed by an integral RF choke built into the stem of 53. Here in Fig.12 in this aspect of the invention, the tuneable element 53 is a thin, conductive, elastic flexible strip mechanically mounted and grounded at the end farthest from the I/O port III, 121 to be tuned, in this case by one or more conductive pillars 971, 972 (which could be vias). An SMA wire 779 is mechanically and preferably electrically connected to an offset / out-of-plane tab 578 of element 53 on one side of 53. The other end of the SMA wire is mechanically mounted to an insulating mount 777 attached to ground plane 11 (not shown) and has an electrical connection point 776 to which a control wire (not shown) is electrically connected. When the controlled heating current is passed through the SMA wire (using in this example the grounded end as return path) the wire heats and contracts controllably causing the thin conductive element 53 to bend out of its natural plane and because of the offset position of the SMA wire (i.e. asymmetric to the principal axes of 53) element 53 will twist and so also bend so that its top edge (where the SMA wire attaches) will no longer be parallel to the axis of I/O port components 111, 121 which will have a strong tuning effect as this is a magnetic tuning element. Similar mechanical and conductivity considerations as applied to the bending element and SMA wire in Fig. 11 apply here too. The net result of this configuration is a very small low cost controllable tuning element that can fit right inside the waveguide allowing no leakage of RF energy.

Fig.13 illustrates another aspect of the present invention and shows a variant of part of the assembly of Fig.4. As previously, 31 is one of the resonators but now instead of being a solid rigid conductor it is instead a thin folded elastic conductive sheet comprising a long face of similar size to the resonator it replaces in Fig4, which has a grounded end (here by two vias 93) and at that end it has also a folded side panel on which is mounted the I/O port assembly 111,121 again as before, which is folded around once more to rejoin the via 93, the rigid U-section so formed designed to keep the location of the I/O port fixed in space. The other end of the long main face has a twice folded over end inside of which can just be seen an insulating mounting point 1030 which serves as a mechanical anchor for an SMA wire 1010 which extends back to the base where the SMA wire it is again anchored on another mounting 1040. Wires carrying controlled heating current for 1010 (not shown for clarity) are attached to each end of SMA wire 1010 the one from the ungrounded end of 31 being run down the inside face of 31 to the grounded base-end where it is effectively Faraday shielded from the RF field on the outside face. When the controlled current heats SMA wire 1010 sufficiently it controllably contracts and in so doing pulls diagonally across the "thickness" of the envelope of 31 causing it to bend significantly which changes its effective electrical length as well as its capacitance to the ground planes and any other grounded surfaces that may conveniently be arranged to lie close to its unbent position. In this way the resonator itself may be controllably tuned with this completely integral SMA-wire actuator, and by suitable arrangement of additional sections of folded pieces of 31 the RE field can be adequately decoupled from the very thin SMA wire 1010, There will be no RE leakage to the outside of the cavity containing resonator 31. Several useful variants of this type of resonator structure by modifying the folded sections of 31 which control its local rigidity, and by moving the end point mechanical attachments of the SMA wire 1010. For example if a much shorter SMA wire is mechanically attached to the inside of the long main section of 31 much closer to the grounded base, and the other SMA wire end moved further away from that face at its base than as drawn in Fig.13, then because of the greater leverage provided by the length of 31 a significantly greater movement of the free tip can be achieved for significantly lower power consumption (which is proportional to SMA wire length), so long as the flexibility of the structure of 31 in the direction of curvature so caused, is kept low enough to enable that degree of bend to be caused by the force capability of the SMA wire (e.g. a maximum of -10 to 15gram for a 25micron SMA wire. Such an arrangement is also significantly easier to Faraday shield the SMA wire from the RF energy in and around the resonator 31.

Fig.14 illustrates another useful deformable form of tuneable resonator 31. This is made of thin folded elastic conductive sheet, e.g. thin metal, and consists of two curved surfaces with facing each other connected at the top (non-grounded end) and optionally also at the bottom (grounded end) with a further piece of the continuous thin conductive sheet. An SMA wire runs up the centre of the inside of the structure and its bottom end 1120 is just visible in its mechanical and electrical insulated mounting 1740, while its top end (not visible in this drawing) is mechanically and electrically mounted to the centre of the top section of 31 joining the top ends of the two curved surfaces. When the SMA wire is controllably heated by a current applied to end 1120by a control wire (not shown) using return current path to ground via the body of resonator 31, the SMA wire within 31 contracts which causes the flexible long curved walls to curve through a tighter radius and thus for the entire resonator structure envelope to shorten changing its inductance as well as its capacitance to the surrounding grounded components (not shown for clarity). The SMA wire is symmetrically placed between the two curved walls and is effectively in a complete Faraday cage, completely isolated from the RF energy in the cavity. The end result is a completely controllably tunable resonator taking up no additional space (over and above that of a solid metal component), having lower mass, very high Q (e.g. the external portion of 31 could be silver plated to a few skin depths at negligible cost) and no leakage of RF energy to the outside of the cavity, and all at very low cost, and high reliability. Another useful variant of this aspect of the present invention is to instead have the two curved surface curving outwards rather than inwards, when more use can easily be made of their capacitance to nearby ground planes for example. This particular curved wall SMA-wire tuned resonator is presented as an illustration of what is possible using thin flexible curved wall structures with an internal Faraday-cage screened SMA wire to actuate the tuning function, and it will be clear to those skilled in the art that an infinite variety of such curved (and curved and straight) shapes can be used in the same way and all such are included herein.

Fig. 15 shows a phase shifter formed by two transmission lines (a vertical Line V and a horizontal Line H) supporting waves of orthogonal polarisations propagating in the direction P, as designated in the picture. This realization shows the two transmission lines formed by conductors 1201 and 1202 (Line V) and conductors 1203 and 1204 (Line H). Slidably mounted plate 1205 is placed orthogonal to the direction of propagation P. It contains a resonating structure 1205 formed by the metal layout and resonating at the frequency of operation to facilitate the reflection of the incoming wave. These structures are designed to resonate at the operating frequency, for example -conductive strips forming dipoles, as shown in the picture. The plate contains two types of structures -designed to interact with the wave of corresponding polarisation. Structures 1206 and 1207 interact with the wave supported by Line V, and structures 1208, 1209 interact with the wave supported by Line H. This configuration of phase shifter provides dual polarised operation with identical phase shift introduced for Vertical and Horizontal polarizations supported by Lines V and H correspondingly. The plate 1205 is moved in the direction of the arrow by an Actuator (not shown).

Fig.16 shows a phase shifter capable of independent control of the phase of two orthogonal polarizations. It is formed of two transmission lines (a vertical Line V and a horizontal Line H) supporting waves of orthogonal polarisations propagating in the direction P, as designated in the picture. Resonating structures designed to interact with the wave of each polarization are placed on dedicated plates. The structures 1306 and 1307 are placed on the plate 1310 and interact with the wave supported by transmission Line V. The resonating structures 1308 and 1309 placed on the plate 1311 are designed to interact with the wave supported by transmission Line H. Each plate has freedom of movement in the directions shown by arrows, and can be moved independently with the help of dedicated slot 1312 that facilitates independent movement of cards 1310 and 1311 relative to each other. The plates 1310 and 1311 arc mechanically connected each to separate Actuators (not shown) which Actuators are capable of independently moving the cards in the direction of the arrow.

Fig.17 shows a phased array antenna comprised of a 2D array of phase shifters, which may be any of the types of phase-shifter actuated by an Actuator, described herein. An RF feeding system 1401 irradiates the antenna array (in transmission mode, which will be described from hereon, but the same device also works similarly in receive mode). Each array element is formed by the metal layout configuration that resonates at the frequency of operation to facilitate the strongest possible interaction with the incoming wave. In Fig.17 the elements are shown realised as dipoles 1403 with geometrical dimensions chosen to obtain maximum interaction with the incoming wave. The dipole metal structures may conveniently be laid out on the surface of a dielectric panel supporting the whole structure (not shown in Fig. 17). Each dipole is connected to an independently variable length transmission line 1404, designed to channel the energy received by the dipole to the reflector 1405. The reflected energy then returns to the dipole with a phase determined by the specific length of each transmission line. The dipole than reradiates the energy with phase as determined by the length of its respective transmission line. The length of each transmission line is independently changed by a mechanically connected Actuator (not shown in the Fig.). The array of phase shifters (for each polarisation independently where dual polarisation structures e,g, as per Fig 16, are used), can be individually positioned so as to form a directional beam of radiation of the reflected waves and form an antenna pattern 1406, for example, as shown in Fig.17, for one polarisation only for clarity --the other polarisation may also be formed similarly into a beam which is independently steerable from the first polarisation in the case of dual polarisation phase-shifters. The direction and shape of the antenna pattern is adjustable by suitable positioning of each of the Actuators connected to the phase-shifters. The array as described may be improved by layering dielectric and metal layers behind all the other elements including the reflectors, to act as a shield and minimise back radiation, which metal layers may advantageously be interconnected with other structures in the array with vial through the thickness of the plane of the antenna.

A further variant of this phased array dispenses with the variable length transmission lines altogether and instead makes the individual dipoles independently moveable orthogonal to the plane of the array, the movement of each being controlled by a dedicated Actuator capable of moving the dipole precisely with 4-bit, or preferably 5-bit or more preferably 6-bit precision. In such an arrangement the dielectric panel supporting the whole structure may now be pierced with an array of slots in which the dipoles move and to which the Actuator stators may conveniently be mounted. Again it is advantageous to add a rear dielectric layer and behind that a plane metal layer, to minimise unwanted rear-radiation.

Claims (52)

1. CLAIMS1. A phase or frequency tuneable device comprising an RF cavity exploiting the thermo-mechanical properties of SMA material in the shape of wires or ribbons or sheets so arranged to form an Actuator applied in such a way as to achieve controllable deformation or controllable movement of the walls of the RF cavity, or controllable movement or controllable deformation of additional electromagnetic structures in the vicinity of or inside the RE cavity, so as to affect the electric and/or magnetic components of one or several of the eigenmodes of electromagnetic field supported by the RF cavity.
2. 2. An RF tuneable filter device comprising two or more devices as per Claim 1 wherein the two or more of the Claim 1 devices are each electromagnetically coupled to at least one other of the plurality of devices.
3. 3. An RF tuneable filter device according to Claim 2 wherein at least one of the electromagnetic couplings between Claim 1 devices is in the form of an iris penetrating the solid walls or ground planes separating the Claim 1 devices or by an iris formed by a gap in a wall of conductive vias separating the Claim 1 devices.
4. 4. An RF tuneable filter device according to Claim 2 wherein at least one of the electromagnetic couplings between Claim 1 devices is formed by the provision of additional non-grounded conductive tracks formed on an insulating layer formed on the inside or outside of one or both of the ground planes sandwiching the cavities to he coupled, and wherein the conductive tracks protrude into both of the adjacent cavities of the Claim 1 devices either without electrical connection to anything else or with both ends grounded.
5. 5. An RF tuneable filter device according to Claim 2 wherein at least one of the electromagnetic couplings between Claim 1 devices is formed by non-grounded cross-coupling wires protruding into both of the cavities of the adjacent Claim 1 devices through an iris either without electrical connection to anything else or with both ends grounded.
6. 6. An RF tuneable filter device as per any of Claims 2, 3, 4, 5 wherein at least one of the electromagnetic couplings between RF cavities of the Claim 1 devices is tuneable by a tuning device comprising SMA material in the shape of wires or ribbons or sheets applied in such a way as to achieve controllable deformation or controllable movement of a conductive or dielectric tuning element in the vicinity of the electromagnetic coupling.
7. 7. An RF tuneable filter device as in any of Claims 1, 2, 3, 4, 5 or 6 with one or a plurality of stages, the filter either being of the low-pass, band-pass, band-stop, high-pass or phase-shifting configuration comprising: two or more spaced conductive ground planes with joining walls connecting between the conductive planes and/or conductive vias positioned between the conductive ground planes, having inside between the ground planes one or a plurality of separate RF cavities separated by solid conductive partitions and/or by a plurality of conductive vias positioned between the conductive planes and in each of those cavities is zero, one or a plurality of resonators or electromagnetic reflectors, and where there is a plurality of cavities each cavity is electromagnetically coupled to at least one other cavity by an iris penetrating the solid walls or ground planes or by an iris formed by a gap in a wall of conductive vias between ground planes, and wherein one or more of the RF cavities has each one or more tuning elements penetrating into or wholly contained within the RF cavity and wherein each such tuning element is either wholly moveable or is deformable in such a way that the movement or deformation thereof changes the electromagnetic characteristics of the RF cavity so as to satisfy the tuneability requirement of the filter and wherein the movement or deformation of at least one of the tuning elements is caused by the expansion and contraction of one or more associated SMA structures each under the heating influence of a controlled electric current passing through said SMA structure and where each SMA structure is located outside of the RF cavity or within the walls of the RF cavity or located wholly within the RF cavity.
8. 8. A tuneable RF filter as in any of the previous Claims with at least one resonator wherein each of the resonators are made of conductive material or are made of low-loss dielectric material or are made of non-conductive material coated or plated with conductive material or are made of some combination of these.
9. 9. A tuneable RF filter as in Claim 8 with at least one dielectric resonator wherein the dielectric resonators are made of high permittivity low loss RF ceramic.
10. 10. A tuneable RF filter as in Claim 8 or 9 wherein one or more of the resonators are in the form of strips or T-shaped strips or rings or spirals or other shapes that resonate at the required frequency.
11. 11. A tuneable RF filter as in Claim 8, 9 or 10 wherein any resonator with geometry that has several cigenmodes (e.g. X-shaped or star-shaped) has concurrent modes in the resonator suppressed by shorting to ground the corresponding ends of the branches of the resonator structure.
12. 12. A tuneable RF filter as in Claim 8, 9, 10 or 11 wherein a more compact assembly is achieved by the use of a dual-mode resonator or a triple-mode resonator with a minimum of two or three mutually orthogonal branches with a single common point; or, a cavity supporting two or three orthogonal modes.
13. 13. A tuneable RF filter as in any of the previous Claims with more than one RF cavity wherein external signal connections are provided in the form of spaced input and output tapping points to the first (input) and the last (output) cavity.
14. 14. A tuneable RF filter as in any of Claims 1 through 12 with only one RF cavity wherein an external signal connection is provided in the form of an input output tapping point to the cavity.
15. 15. A tuneable RF filter as in any of the previous Claims with at least one resonator and at least two RF cavities wherein one or more of the resonators and zero, one or more of the inter-cavity couplings and zero, one or both of the input and output tapping points has each a tuning element penetrating into the resonator's RF cavity or sited wholly within the cavity such that the movement or deformation thereof changes the capacitive loading or inductive loading or both of the associated resonator or coupling or tapping point, and wherein said movement or deformation of the tuning element is controllably caused by the controlled heating of one or more SMA-wires sited outside or partially or wholly within the RF cavity.
16. 16. A tuneable RF filter as in any of the previous Claims with at least one resonator wherein one or more of the resonators sited within an RF cavity is caused controllably to change shape or mechanically deform by the controlled contraction of at least one controllably heated SMA-wire such that the movement or deformation thereof changes the self capacitance or inductance or both of the associated resonator in such a way as to controllably tune the resonator.
17. 17. A tuneable RF filter as in any of the previous Claims with at least one tuning element wherein each tuning element has the shape of a thin strip, or a rod, or a bar, or a tube, or more generally a long prismatic section with flat or curved surfaces.
18. 18. A tuneable RF filter as in Claim 17 wherein the tuning elements are made of conductive material or are made of low-loss dielectric material or are made of nonconductive material coated or plated with conductive material or are made of some combination of these.
19. 19. A tuneable RF filter as in Claim 18 wherein dielectric tuning elements are made of high permittivity low loss RF ceramic or alternatively are made from a glass wafer.
20. 20. A tuneable RF filter as in Claims 17, 18 or 19 wherein one or more tuning elements that is tuning a resonator is aligned in the same direction of greatest extension as the resonator that they are tuning so that the gap between the tuning element and the resonator is also aligned with the resonator.
21. 21. A tuneable RF filter as in any of the previous Claims with at least one resonator wherein one or more resonators has a longitudinal slot in it into which a tuning element may fit without touching the resonator so as to increase the variability of capacitance between the tuning clement and resonator.
22. 22. A tuneable RF filter as in any of the previous Claims with at least one resonator wherein one or more resonators has a longitudinal slot in it into which a tuning element may fit without touching the resonator so as to increase the variability of self-inductance per unit of length of the resonator.
23. 23. A tuneable RF filter as in any of the previous Claims with at least one conductive tuning clement extending outside the RF cavity wall, wherein RF isolation for the portion of the tuning element protruding outside the cavity is provided by integrating an RF choke into the structure of the tuning element around the region where it exits the cavity and enters the cavity wall and optionally beyond.
24. 24. A tuneable RF filter as in Claim 23 wherein a simple integral low-pass RF choke is realised by a capacitive load at the external end of the tuning element sufficiently large to be considered an RF short.
25. 25. A tuneable RF filter as in Claim 23 wherein a more effective RF choke is formed by a sequence or series of one or more inductive sections each followed by a parallel capacitive section positioned down the length of the tuning element from the cavity to the external end of the element, the inductive sections being narrower and the capacitive sections being wider.
26. 26. A tuneable RF filter as in any of the previous Claims with more than one tuning element wherein the tuning elements are each caused to move by one or more Actuators, with one or more of the tuning elements sharing an Actuator, such that the total number of Actuators can vary from one in the case that all of the tuning elements are moved by the same Actuator, up to the total number of tuning elements in the case that each tuning element is driven independently of all of the others by its own Actuator.
27. 27. A tuneable RF filter as in any of the previous Claims wherein each Actuator may be implemented as an SMA-wire actuator and wherein the length of one or more sections of SMA wire are caused controllably to change by controllably changing the SMA wire temperatures.
28. 28. A tuneable RF filter as in Claim 27 wherein the temperature of an SMA wire is changed by controlling the RMS electric current passing through the SMA wire and wherein the current is under the control of a programmable device such as a microprocessor.
29. 29. A tuneable RF filter as in any of the previous Claims wherein one or more of the Actuators are mechanically connected either directly or indirectly between the tuneable filter body and the moveable or deformable elements of the tuneable filter so causing the moveable filter elements to move relative to the filter body or to deform.
30. 30. A tuneable RF filter as in any previous Claim wherein one or more of the Actuators are mechanically connected only to the filter component that is designed to deform with no mechanical connection required between the Actuator(s) and the RF filter body.
31. 31. A tuneable RF filter as in any of the preious Claims wherein one or more of the Actuators are mechanically connected only between two of the filter components that are required to move relative to each other with no mechanical connection required between the Actuator(s) and the RF filter body.
32. 32. A tuneable RF filter as in any of the previous Claims wherein the mechanical linkage of a tunable element to its respective Actuator is direct and immediate constituting a fully integrated actuator such that part of the tuneable element itself is used as part of the actuator structure.
33. 33. A tuneable RF filter as in any of the previous Claims with at least one tuning element made of a dielectric material and the associated Actuator not wholly separated from the inside of a respective cavity by the solid conductive wall of the cavity is RF electrically isolated by the suitably close positioning to the tuning element of one or more conductive vias connecting between the conductive walls of the cavity.
34. 34. A tuneable RF filter as in any of the previous Claims with at least one tuning element made of a conductive material wherein TEM mode propagation along the tuning element of RF energy from within the cavity to the outside of the cavity and towards its associated Actuator is prevented by two or more buried vias located adjacent to and across the longitudinal line of the tuning pin and separated by the appropriate interval which is approximately a half-wavelength but corrected for the reactance introduced by the adjacent vias, for the propagation at this wavelength to be blocked and which capacitively loads the leaking TEM mode to stop the leakage.
35. 35. A tuneable RF filter as in any of the previous Claims with more than one Actuator in total controlling the movement of the totality of tuning elements wherein the synchronisation of the movements of all of the tuning elements is electrically controlled by the synchronisation of the appropriate control signals to the plurality of Actuators, for example by means of a pre-computed look-up table kept in the memory of the controller or by a real-time algorithm generating the actual required positions of all tuning elements to achieve the required state of the filter.
36. 36. A tuneable RF filter as in any of the previous Claims with at least one moveable tuning clement wherein each movcablc tuning clement is movably supported by a tuning support structure (Support) which may be partially or fully dielectric or partially or fully conductive.
37. 37. A tuneable RF filter as in any of the previous Claims wherein each SMA wire is enclosed within a dedicated void in one of the one or more Supports to ensure free movement of the SMA wire relative to the Support.
38. 38. A tuneable RF filter as in any of the previous Claims with at least one moveable tuning element wherein each movcablc tuning element is positioned slidably in a channel through the Support to ensure free movement of the tuning element while maintaining a precise gap between and accurate distance from the tuning pin to the corresponding resonator, coupling or tapping point for all positions of the tuning element controlled by the associated Actuator.
39. 39. A tuneable RF filter as in any of the previous Claims wherein each Actuator is fully integrated into the filter, for example by being buried inside the Support.
40. 40. A tuneable RF filter as in any of the previous Claims with at least one resonator wherein one or more resonators are movably mounted within a cavity and caused to so move by direct or indirect mechanical connection to one or more SMA-wires.
41. 41. A tuneable RF filter as in any of the previous Claims with at least one resonator wherein one or more resonators are constructed so as to be deformable and are caused to so deform by direct or indirect mechanical connection to one or more SMA-wires.
42. 42. A tuneable RF filter as in Claim 41 wherein one or more of the deformable resonators has the form of a thin strip, a flat-section spiral, a flat-section helix or another shape which has at least one direction of easy (low force) deformation.
43. 43. A tuneable RF filter as in Claims 41 or 42 wherein one or more of the deformable resonators is made of elastic material such that it returns to its original shape after deformation and is capable of providing the necessary restoring force to stretch to its original cold length the SMA-wire that upon heating caused its deformation, once the SMA-wire has cooled again.
44. 44. A tuneable RF filter as in Claims 41, 42 or 43 wherein the shape of the deformable resonator is such as to effectively enclose the SMA wire in a Faraday cage and so isolate it from the RF energy in the surrounding RF cavity.
45. 45. A tuneable RF filter as in any of the previous Claims wherein the SMA wire or wires provided to cause motion of the tuning clement, are attached to the low-impedance capacitive sections of the tuning element so as to maximally isolate them from any RF energy transmitted from within the cavity.
46. 46. A tuneable RF filter as in any of the previous Claims with an SMA-wire positioned partly or wholly within an RF cavity wherein strong coupling of the SMA-wires to the RF field in the cavity is prevented by the use of a very thin (<100micron diameter) straight SMA wire located entirely on or within the electric wall of the cavity, or alternatively by positioning the line of the wire orthogonal to and symmetrical to the magnetic walls of the cavity and parallel to the electric walls of the cavity.
47. 47. A tuneable RF filter as in any of the previous Claims with an SMA-wire positioned partly or wholly within an RF cavity wherein the SMA-wire or the SMA-wire together with its electrical connections (e.g. to an external wire-temperature controller) are constrained to lie in a plane and that plane is positioned orthogonal to and symmetrical to the magnetic walls of the cavity and within the electric walls of the cavity
48. 48. A tuneable RF filter as in any of the previous Claims wherein one or more resonant or reflective elements are positioned in a waveguide with conductive walls and wherein the one or more resonant or reflective elements are caused to move axially along the waveguide each by an Actuator.
49. 49. A tuneable RF filter as in the previous Claim wherein the waveguide conductive walls are formed from alternate metal and dielectric layers with adjacent metal layers joined together by rectangular arrays of conductive vias through the dielectric layers the rectangular arrays forming the walls of the waveguide whose axis is orthogonal to the metal and dielectric layers, and the waveguide cavity is formed by the removal of the dielectric and metal layers within and between the waveguide walls.
50. 50. A tuneable RF filter as in Claims 48 or 49 wherein the one or more resonant or reflective elements are constructed so as to reflect as perfectly as practically possible all of the RF energy incident at one end of the waveguide back to that same end of the waveguide with a phase directly proportional to the axial position of the moveable elements along the waveguide thus providing a single-port reflective tuneable phase-shifting filter.
51. 51. A tuneable RF filter as in Claims 48 or 49 with two resonant or reflective elements constructed so as to reflect as little as practically possible of the RF energy incident at one end of the waveguide back to that same end of the waveguide such that nearly all of the RF energy emerges from the other end of the waveguide with a phase directly proportional to the axial positions of the moveable elements along the waveguide and wherein a second Actuator is used to control the axial separation of the two resonant or reflective elements to optimise the input return loss with operating frequency thus providing a dual-port tuneable phase-shifting filter.
52. 52. A tuneable RF filter as in Claims 48 or 49 or 50 or 51 with two separate sets of one or more resonant elements each set independently of the other moveable axially along the waveguide by independently controllable Actuators, wherein each set of resonant elements is responsive to only one of two different polarisations of waves incident on one end of the waveguide, for plane polarisation waves the different polarisations being orthogonal to each other, and for circular polarisation the different polarisations being of opposite sign.