WO2018069864A1

WO2018069864A1 - Tunable band-pass filter

Info

Publication number: WO2018069864A1
Application number: PCT/IB2017/056321
Authority: WO
Inventors: Luca Pelliccia; Roberto Sorrentino
Original assignee: RF MICROTECH Srl
Current assignee: RF MICROTECH Srl
Priority date: 2016-10-12
Filing date: 2017-10-12
Publication date: 2018-04-19
Anticipated expiration: 2019-04-12
Also published as: IT201600102172A1

Abstract

Tunable band-pass filter that allows to reconfigure its frequency response thanks to a tuning mechanism of the resonance frequency of the resonant cavities. The mechanism is inserted inside each guide filter resonator to obtain the tuning of the band-pass of the filter, thus obtaining a filter which can be reconfigured for microwave applications.

Description

"TUNABLE BAND-PASS FILTER"

FIELD OF THE INVENTION

The present invention concerns a tunable band-pass filter.

In particular, the band-pass filter according to the present invention can be the rectangular-guide microwave type that allows its frequency response to be reconfigured thanks to a mechanism for tuning the resonance frequency of the resonance cavities (also called resonators) that make up the filter.

The present invention comprises a specific mechanical control device inserted inside each resonator of the guide filter to obtain manual or electronic tuning of the band-pass filter, thus obtaining a reconfigurable filter for microwave applications ("microwave reconfigurable filter" or "microwave tunable filter").

BACKGROUND OF THE INVENTION

It is known that filters are used in radio frequency microwave systems to allow the passage of a (generally narrow) portion of the spectrum of frequencies and to suitably attenuate the other frequencies.

As is known, band-pass filters made in cavities or metal waveguides are currently used in high-frequency transmission/reception systems for applications where low losses and high operational power are fundamental requirements. However, against the advantages of the technology of cavities and metal waveguides in terms of low losses and high power, there are disadvantages of various types, such as manufacturing costs, high bulk and weight. The latter are considerably greater than in other technologies, such as that for example of printed circuits, commonly known as planar circuit technology, but which does not, however, offer similar performance in terms of low losses and high power.

One known guide filter consists of a guide with metal walls (generally with a rectangular section: in this case it is referred to as a rectangular guide filter), inside which there are 'N' resonators (made as empty guide sections), also called resonant cavities, separated by discontinuities (which act as coupling elements) which, suitably sized, allow to control the response of the filter. The number of resonators 'N' that makes up a guide filter determines the order of the filter: a filter with 'N resonators' is an 'N' order filter. In each resonator the electromagnetic field resonates at a given frequency, called the resonance frequency, and that frequency is the operating frequency of the filter itself and depends, in an inversely proportional manner, on the size of the resonator (length, width and height).

For a number of years, the number of frequency channels that require dedicated band-pass filters has been increasing, along with the number of related versions of channel filters that have to work at different operating frequencies and in different channels.

The waveguide filter, where guide or cavity trunks are connected and coupled by means of transverse discontinuities such as irises or metal cylinders (known as posts), is one of the most common choices, called "direct-coupled cavity filter". Among these, typically, inductive iris filters are preferred.

On the other hand, we talk about "E-plane" guide filters when the interconnection and coupling sections between the resonant cavities of the filter are made with rectangular guide trunks loaded with metal ridges, which have the same height as the guide and lie in the plane E, that is, in the longitudinal plane parallel to the electric field of the fundamental mode TE10 of the rectangular guide and centered with respect to the section of the guide itself. E-plane filters offer significant advantages, the main ones being the low production costs and the stability of the couplings as the pass band of the filter varies. This last advantage allows to avoid the introduction of particular and complex features necessary, for example, for inductive iris filters, to ensure the stability of the filter response with tuning.

In order to reduce and potentially annul the costs and bulk associated with guide filter technology, various types of reconfigurable filters (also known as "tunable" filters) have been proposed over the last few years, which allow to use the same filter to work in different frequency channels and with different responses. In this way, only one component can be used for multiple frequency bands, reducing the number of pieces needed, and thus the bulk, in an apparatus, and also reducing design and manufacturing costs.

The most common and well-known tuning method for guide structures provides to use metal or dielectric screws (also known as "tuning screws") typically parallel to the electric field (that is, in plane E), and typically inserted where the latter has maximum intensity, that is, at the center of the guide itself. Tuning screws perturb the electromagnetic field, modifying the resonance frequencies of the resonators of the filter and/or the couplings between them, thus producing the tuning of the filter itself.

However, this type of mechanical tuning, which is widely used, is not easily implementable in some guide structures, such as E-plane filters where the tuning screw would be exactly in correspondence with the metal ridges at the center of the rectangular guide. Furthermore, the automatic control mechanisms of the tuning screws are generally complex and expensive.

Various documents are known which describe methods for adjusting and tuning E-plane filters, using mobile lateral walls, for example in US-A- 5,808,528, or field perturbator elements having a longitudinal axis, for example in document US-A-2012/126914, thus obtaining a simultaneous reconfiguration of all the cavities in cascade that are affected by the mobile wall or the longitudinal field perturbator element. These solutions do not allow localized and differentiated reconfigurations in the individual sections of the filter guide, that is, differently for each resonant cavity.

In particular, the solution described in US-A-2012/126914 provides a single rotatable element which occupies a significant portion of the volume of the filter guide, having to pass through all the resonators. This solution has low performance in terms of filter insertion losses. Moreover, this solution does not allow to use a metal rotatable element since the response of the filter would be compromised both in terms of insertion losses and also in terms of adaptation of the pass-band since the couplings of the filter (determined by the longitudinal metal ridges in the guide) would be significantly altered.

Other methods for tuning filters that use electronic rather than mechanical devices - such as pin diodes, varactor diodes or RF MEMS - have been proposed in WO-A-2012/016584 and in the publication by Peroulis, D.; Naglich, E.; Sinani, M.; Hickle, M., "Tuned to Resonance: Transfer-Function-Adaptive Filters in Evanescent-Mode Cavity-Resonator Technology", IEEE Microwave Magazine, vol.15, no.5, pages 55,69, July-Aug. 2014. All these methods, however, lead to higher insertion losses than those obtainable with mechanical solutions. The electronic devices and their corresponding polarization and actuation circuits that must necessarily be inserted inside the guide itself, in fact, greatly degrade the quality factor, increasing losses.

Other known solutions are described in documents CN-A- 101640301, US-A- 3.495.192, US-A-2014/0028415, US-A-2014/0132370, US-A-2015/0180105, US-A-2015/0180106 which use devices rotatable inside resonant cavities and not made by E-plane type guide filters, but by other types of cavity filters.

These solutions, however, require specific design and manufacturing strategies to ensure the stability of the response with the tuning.

These design and manufacturing strategies are needed to compensate for the unwanted variation of the internal and external couplings as the tuning varies, thus requiring greater design and manufacturing complexity.

Documents US-B-7,456,711 and US-A-2014/132370 also describe band-pass filters provided with rotating objects that perturb the electromagnetic field of the resonators to obtain the desired tuning of the filter.

The perturbation occurs either electrically (with electronic components such as diodes, varactors or transistors), or electro-mechanically (that is, by MEMS devices, that is, Micro-Electromechanical Systems), or mechanically.

The purpose of the present invention is to obtain a tunable band-pass filter that is simple and economical to achieve.

It is also a purpose of the present invention to obtain a tunable band-pass filter that allows to increase the operating power with low losses.

It is also a purpose of the present invention to obtain a tunable band-pass filter in which the form of the filter response does not deform with the tuning.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above purposes, a tunable band-pass filter for microwave and radiofrequency applications in E-plane technology comprises a first body and a second body coupled with respect to each other with respective coupling surfaces. The first body and the second body are each provided, in respective coupling surfaces, with a longitudinal groove. The longitudinal grooves of the first body and the second body, together define a waveguide cavity that extends through along a longitudinal axis.

In accordance with one aspect of the present invention, the band-pass filter comprises a plate interposed between the coupling surfaces of the first body and the second body and is provided with a plurality of through holes at least partly disposed in the waveguide cavity. The through holes define with the waveguide cavity corresponding resonant cavities.

In accordance with another aspect of the present invention, the band-pass filter comprises a plurality of perturbator bodies each of which is at least partly installed in the waveguide cavity and located in through manner through a respective one of the through holes.

According to another aspect of the present invention, at least one mechanical actuation device is installed externally to the waveguide cavity and is connected to at least one of the perturbator bodies in order to modify the position of the perturbator body in the resonant cavity and modify the resonance frequency of the respective resonant cavity.

In accordance with a possible embodiment of the invention, the mechanical actuation device is configured to adjust at least the angular position of said perturbator body with respect to an axis of rotation transverse to said longitudinal axis.

The perturbator bodies, depending on their angular position, perturb the electromagnetic field of the resonant cavities that make up the filter, varying the resonance frequency thereof and therefore allowing the frequency movement of the electric response of the filter.

The band-pass filter as described above allows to modify its frequency response (tuning) by simple frequency translation, keeping, however, the same form (pass band width, level of band adaption, rejection levels outside the pass band).

The present invention also allows to overcome the limits of the solutions described above by using a rotatable perturbator body able to produce local perturbations of the electromagnetic field of the resonant cavity, so as to vary the resonance frequency thereof. The present invention overcomes the known solutions cited above in terms of performance because it does not use electronic devices that decrease the quality factor of the component, and it does not use mechanical devices that extend according to the length of the guide. This allows the band-pass filter of the present invention to be individually tuned in each of its parts, that is, in every one of its resonant cavities.

Indeed, the present invention allows to perturb the electromagnetic field, even only locally, in a different way for each resonant cavity of the band-pass filter. This allows to have available a larger number of degrees of freedom, tuning the different resonant cavities individually or the different sections of waveguide. Thanks to this advantage, the present invention also allows to compensate for errors due to manufacturing tolerances or local variations due to heat dilations and contractions of the materials.

Advantageous embodiments of the present invention are applied to the specific case of rectangular guide filters of the E-plane type with entrances in rectangular waveguide.

The particular type of electromagnetic coupling of the resonant cavities of an E-plane type filter, made using longitudinal metal ridges of various length located in the central plane of the waveguide cavity, is very stable as the resonance frequency of the cavities varies. This property ensures that the filter band itself remains stable (that is, with a good adaptation and constant width) inside a certain range of frequency variation (5-10%).

Furthermore, all the couplings of the solution proposed here, whether they are external (that is, toward the entrance and exit guides) or internal (between adjacent resonators), are made using E-plane metal ridges.

It is important to underline, moreover, how with the same method presented here it is also possible to design and produce other devices that can be reconfigured in waveguide which contain band-pass filters, such as for example diplexers and multiplexers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. 1 is an exploded schematic view of a tunable band-pass filter in accordance with embodiments of the present invention;

- fig. 2 is a schematic view of a cross section of the band-pass filter of fig. 1 ;

- figs. 3-6 are partial schematic views of a tunable band-pass filter, with perturbator bodies located in different operating positions;

- fig. 7 shows a graph of the transfer function measured with laboratory instruments, suitably calibrated (in the form of scattering parameters) of a tunable filter made according to the invention described here and measured in correspondence with three different combinations of the angular positions of the perturbator bodies.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The present invention concerns a tunable band-pass filter indicated in its entirety by the reference number 10.

The band-pass filter 10 according to the present invention is used for microwave and radiofrequency applications in E-plane technology.

The band-pass filter 10 comprises a first body 11 and a second body 12 coupled together with respective coupling surfaces 13.

In particular, it can be provided that the first body 11 and the second body 12 are made of a metal material. The use of metal material is intended to contain and guide the electromagnetic field.

By way of example only, the first body 1 1 and the second body 12 are made of a material selected from a group comprising steel and copper.

According to a possible solution, the first body 1 1 and the second body 12 can be made of aluminum. This allows to obtain a band-pass filter 10 that is extremely light, easy-to-work, and economical.

The first body 11 and the second body 12 coupled with each other can define an oblong prismatic element, also referred to in this particular field as a guide, having, for example, a substantially rectangular cross-section shape.

According to possible solutions, the first body 1 1 and the second body 12 can have substantially the same shape and, when coupled, can be symmetrical to each other.

According to possible solutions, the coupling surfaces 13 can be substantially flat and, during use, lie substantially on the same plane. In the case of an E-plane band-pass filter, the lying plane of the coupling surface can define said plane E. The E-plane band-pass filter, which is defined by the teachings of the present invention, allows to provide a more stable electric response as the frequency tuning varies compared to other types of guide filters. By stable we mean that the variation in the width of the band-pass is less than 10% or that the band adaptation remains better than -15dB.

According to possible solutions, the first body 11 and the second body 12 can be reciprocally coupled with each other by means of connection elements, for example mechanical.

According to a possible solution, the connection elements can be selected from a group comprising threaded connection elements, plugs, pins, or suchlike.

According to possible variant embodiments, the first body 11 and the second body 12 can be solidly coupled with each other for example by gluing or welding.

According to one aspect of the present invention, the first body 11 and the second body 12 are each provided, in the respective coupling surface 13, with a longitudinal groove 14. In the condition where the first body 1 1 and the second body 12 are coupled with each other, the longitudinal grooves 14 define a waveguide cavity 15 that extends through along a longitudinal axis Z.

In particular, it can be provided that the longitudinal groove 14 is made open toward the outside in correspondence with the respective coupling surface 13. In particular, the waveguide cavity 15 extends in through manner through two opposite ends of the oblong prismatic element defined by the coupling of the first body 11 and the second body 12.

According to possible solutions, at least the surfaces defining the waveguide cavity 15 can be made of a metal material to allow to contain and guide the electromagnetic field. According to this solution, it can be provided that the first body 1 1 and the second body 12 are made of metal material so that the surfaces defining the longitudinal grooves 14 are metal. According to an alternative, it can be provided that the first body 11 and the second body 12 are made of a non- metal material and the surfaces defining the longitudinal grooves 14 are coated with a metal layer, for example by metallization.

According to a possible solution, it can be provided that the metal layer is made of silver or gold which has high electric conductivity, to improve performance in terms of insertion losses in the electric response of the band-pass filter 10.

According to possible solutions, the waveguide cavity 15 has a section transverse or orthogonal to the longitudinal axis Z, with a substantially rectangular shape. This solution allows to obtain a rectangular waveguide cavity 15 in E-plane technology, particularly suitable for microwave and radiofrequency applications.

By way of example only, the cross section of the waveguide cavity 15 has a width W and a height H which is comprised between 0.25 and 0.75 times the width W of the waveguide cavity 15.

The width W of the waveguide cavity 15 is determined along a plane orthogonal to the lying plane of the coupling surfaces 13 and parallel to the longitudinal axis Z.

The height H of the waveguide cavity 15 is determined in a direction parallel to the coupling surface 13.

According to possible solutions, the longitudinal groove 14 made in the first body 11 is substantially equal and symmetrical to the groove 14 made in the second body 12.

This solution allows to minimize inevitable increases in insertion losses that occur due to the fact that the guide is not defined by a single body but by two joined bodies, and that the electric currents that flow on the internal surfaces are interrupted by the cuts. The use of equal and symmetrical grooves 14 allows to obtain an interruption, in correspondence with the reciprocal coupling zone between the two bodies, which is centered and causes the currents that in that plane are parallel to the longitudinal axis Z, not to be cut and therefore the contributions to the insertion losses due to the cuts in the guide are minimized.

According to another aspect of the present invention, the band-pass filter 10 comprises a plate 16 which is interposed, during use, between the coupling surfaces 13 of the first body 1 1 and the second body 12. The plate 16 can be made of a metal material.

According to a variant embodiment, it can be provided that the plate 16 is made of mixed materials, for example with a suitably shaped dielectric substrate and a metallized layer deposited on at least one of its flat surfaces.

The plate 16 also defines a division of the waveguide cavity 15 into two parts, which define the longitudinal grooves 14 of the first body 11 and the second body 12.

According to possible embodiments, the plate 16 can have a thickness comprised between 0.1mm and 5mm, preferably between 0.5mm and 3mm.

The plate 16 is provided with a plurality of through holes 17, in the case shown in figs. 1, 3-6, four through holes 17.

The through holes 17 are located during use at least partly in the waveguide cavity 15 and put the longitudinal grooves 14 in communication with each other.

According to possible solutions, the through holes 17 can have a substantially rectangular shape.

According to possible variant embodiments, the through holes 17 can have a circular or elliptical shape.

The through holes 17 can, however, also have shapes completely different from those described above.

According to some solutions of the present invention, the through holes 17 are disposed aligned with each other in a direction parallel to the longitudinal axis Z.

The through holes 17 are reciprocally separated from each other by separation ridges 18, defined by the plate 16.

The ridges 18 can have determinate sizes or widths, in a direction parallel to the longitudinal axis Z, that are equal to or different from each other. By way of example only, it can be provided that the longer the ridges 18, the narrower is the band.

The ridges 18 define the coupling elements of the band-pass filter 10, that is, the design parameters of the band-pass filter 10, which determine the form of the pass band of the filter, such as the relative bandwidth and adaptation level.

Each through hole 17 defines with the waveguide cavity 15 a respective resonant cavity 19, also called a resonator.

The resonant cavities 19 can be disposed aligned, one in succession to the other, or in cascade, along the longitudinal axis Z.

The number of through holes 17, and therefore the resonant cavities 19, defines a corresponding number of the order of the filter.

According to possible solutions of the present invention, the plate 16 can have a length LF (see fig. 6) in a direction parallel to the longitudinal axis Z, which is less than the length LG of the first body 11 and the second body 12.

The plate 16 is installed between the first body 11 and the second body 12 so that at least one first portion 21 and a second portion 22 of the waveguide cavity 15, respectively located in correspondence with the entrance end and the exit end of the waveguide cavity 15, are without the plate 16, that is, they are not affected by it.

The first portion 21 and the second portion 22, without the plate 16, allow the electromagnetic field entering and exiting from the waveguide cavity 15 to be not perturbed. This also allows to simplify the conventional interconnection flanges in rectangular waveguide. The flanges, in fact, allow to connect the band-pass filter 10 with other devices located upstream and downstream.

According to one aspect of the present invention, the band-pass filter 10 comprises a plurality of perturbator bodies 23 each of which is at least partly installed in the waveguide cavity 15 and is located in through manner through a respective through hole 17.

The positioning of the perturbator bodies 23 in correspondence with the through holes 17 or the resonant cavities 19 allows to position the perturbator bodies 23 where it is more useful to perturb the electromagnetic field of the resonant cavity 19 without altering it excessively, thus compromising the resonance of the field itself, and not near the metal ridges 18 longitudinal to the guide, thus avoiding altering the couplings of the filter and compromising the stability of the filter's electric response during rotation of the perturbator bodies 23.

According to one embodiment of the invention, the perturbator bodies 23 are selectively rotatable, in the manner described below, around respective axes of rotation X which are located transversely to the longitudinal axis Z, in this specific case orthogonal to the longitudinal axis Z and the coupling surfaces 13.

The rotation of the perturbator body 23 perturbs the electric field of the resonant cavity 19 and thus modifies the resonance frequency of the latter, allowing the frequency shift of the response of the band-pass filter 10.

According to a possible solution, the perturbator bodies 23 installed in the waveguide cavity 15 have the same shape and size. This solution allows to obtain a modular structure with a limited cost.

According to a possible variant embodiment, the perturbator bodies 23 have different shapes and/or sizes from each other, or at least some of them. The use of perturbator bodies 23 of different shapes allows, for example in applications where it is not possible to use perturbator bodies of the same shape and size, to obtain a correct tuning of the filter response.

According to a possible embodiment, the perturbator bodies 23 are installed in the waveguide cavity 15 aligned along the longitudinal axis Z.

The perturbator bodies 23 can be made of a dielectric material.

The use of some dielectric materials, for example ceramics with high relative permittivity (>10), allows to perturb the magnetic field significantly, while at the same time limiting insertion losses.

According to a variant embodiment, the perturbator bodies 23 can be made of a metal material. This solution allows to simplify the operations to make the perturbator bodies 23, making them particularly economical. Moreover, the use of metal material makes the perturbator bodies 23 particularly resistant and usable for bigger tuning ranges while keeping the same size.

According to another variant embodiment, the perturbator bodies 23 can be partly made of a metal material and partly of a dielectric material. This solution allows to facilitate the operations to make the perturbator bodies 23.

According to a possible variant embodiment, the perturbator bodies 23 can comprise a perturbator element 24 and at least one support shaft 25 configured to support the perturbator element 24 in the waveguide cavity 15.

The perturbator element 24 can be plate-shaped, as shown in figs. 1-6.

According to possible variant embodiments, the perturbator element 24 can have any shape, even irregular. By way of example only, it can be provided that the perturbator element 24 does not have a circular symmetry with respect to its axis of rotation. In this way it is possible to allow a different perturbation of the magnetic field during the rotation of the perturbator bodies, that is, when they change their relative position with respect to the maximum or minimum points of the electromagnetic field in the resonant cavity 19.

According to possible solutions, the perturbator element 24 has a symmetrical conformation with respect to at least one of its axes of symmetry, and the support shaft 25 is configured to support the perturbator element 24 around the axis of symmetry.

According to a possible variant embodiment, the support shaft 25 is configured to support the perturbator element 24 on a non-symmetrical axis of the perturbator element 24.

According to the solution shown in figs. 1-6, the perturbator element 24 can have a rectangular shape and can be supported by the support shaft 25 in correspondence with the centerline of the perturbator element 24.

According to a possible solution (figs. 1-5), the support shaft 25 can be configured to support the perturbator element 24 on opposite sides of the latter. According to a variant embodiment, see fig. 6, the support shaft 25 is configured to support the perturbator element 24 with one free end, that is, to support the perturbator element 24 cantilevered.

The perturbator bodies 23 can be installed on at least one of either the first body 1 1 or the second body 12, for example by means of support elements 26. The support elements 26 can be selected from a group comprising at least one of either a bushing, a sleeve, or a bearing.

According to possible solutions, at least one of either the first body 11 or the second body 12 can be provided with support seatings 27 configured to support and allow the movement of the perturbator bodies 23.

According to possible solutions, the support seatings 27 are made at least partly open toward the waveguide cavity 15.

The support elements 26 can be installed in the support seatings 27 to support the perturbator body 23.

According to another aspect of the present invention, the band-pass filter 10 comprises at least one mechanical actuation device 28 (fig. 2) installed outside the waveguide cavity 15 and connected to at least one of the perturbator bodies 23 to modify the position of the latter in the cavity and to obtain a consequent change in the resonance frequency of the respective resonant cavity 19. The positioning of the mechanical actuation device 28 externally to the waveguide cavity 15 allows to reduce the electromechanical losses and therefore to increase the efficiency of the band-pass filter 10. Moreover, this positioning makes the operations to adjust the tuning of the band-pass filter 10 much easier. The mechanical actuation device 28 can be selected from a group comprising at least one of either a gear mechanism, a motor, a linear actuator, an articulated mechanism, an actuation lever or crank or a possible combination of the above.

According to a possible solution, the mechanical actuation device 28 is configured to adjust at least the angular position of the perturbator body 23 with respect to the axis of rotation X which is located transverse to the longitudinal axis Z.

By way of example only, it can be provided that the rotation needed to obtain the maximum perturbation effect on the resonance frequency can even be only 90°.

According to a possible solution, the mechanical actuation device 28 can be configured to move the perturbator body 23 linearly in the respective resonant cavity 19. By way of example only, it can be provided that the mechanical actuation device 28 is configured to move the perturbator body 23 linearly and in a direction parallel to the axis of rotation X as defined above, in order to modify its positioning in the waveguide cavity 15.

According to possible variant embodiments, the mechanical actuation device 28 can be configured to move, in a combined manner both linear and rotating, the at least one perturbator body 23.

Embodiments of the present invention can provide that the at least one mechanical actuation device 28 is configured to make all or at least part of the perturbator bodies 23 rotate synchronously. This solution allows to obtain a synchronous tuning, that is, with the same frequency value, of all the resonators of the filter. This allows to obtain a stable tuning of the response of the filter, avoiding unwanted variations in the filter response as the frequency varies.

Variant embodiments of the present invention can provide that the at least one mechanical actuation device 28 is configured to make the perturbator bodies 23 rotate asynchronously. This solution allows to use the present invention also for applications where, for example, it is necessary to correct manufacturing errors (which can adversely affect the form of the filter's electric response), or it can be useful to tune the different resonators with independent perturbator bodies independently and by small quantities.

According to some solutions of the invention, the band-pass filter 10 comprises a single mechanical actuation device 28 connected to all the perturbator bodies 23 in order to move them synchronously inside the respective resonant cavities 19.

According to possible solutions, each perturbator body 23 is connected to its own mechanical actuation device 28 to move it autonomously from the others. The at least one mechanical actuation device 28 can be connected to the perturbator body 23 in correspondence with the support shaft 25 of the latter.

In this embodiment, it can be provided that at least part of the support shaft 25 extends through, in a support seating 27 made in at least one of either the first body 1 1 or the second body 12 and has a free end located externally to the first body 11 and to the second body 12 and connected to the mechanical actuation device 28.

Advantageously, according to the invention the reconfigurable filter can be used in a circuit or device for more complex microwave applications, in this way comprising at least one tunable band-pass filter 10 as described above (for example: a diplexer (that is, a circuit comprising two band-pass filters 10) or a multiplexer (that is, a circuit comprising a plurality of band-pass filters 10)).

Fig. 6 shows the transfer function measured with suitably calibrated laboratory instrumentation in the form of scattering parameters: |s21| and |sl l | expressed in dB) of a band-pass filter 10 re-configurable in band X (8-10 GHz) made according to the invention described here and measured in correspondence with three different combinations of the angular positions of the perturbator bodies 23 located inside the respective resonant cavities 19.

It is clear that modifications and/or additions of parts can be made to the bandpass filter 10 as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of band-pass filter 10, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Tunable band-pass filter for microwave and radiofrequency applications in E- plane technology, comprising a first body (11) and a second body (12) coupled with respect to each other with respective coupling surfaces (13), said first body (11) and said second body (12) each being provided, in the respective coupling surface (13), with a longitudinal groove (14), and said longitudinal grooves (14) together defining a waveguide cavity (15) that extends through along a longitudinal axis (Z), characterized in that it comprises a plate (16) interposed between the coupling surfaces (13) of said first body (11) and said second body (12) and provided with a plurality of through holes (17) at least partly disposed in said waveguide cavity (15), said through holes (17) defining with said waveguide cavity (15) corresponding resonant cavities (19), in that it comprises a plurality of perturbator bodies (23) each of which is at least partly installed in said waveguide cavity (15) and is located in through manner through a respective one of said through holes (17), and in that at least one mechanical actuation device (28) is installed externally to said waveguide cavity (15) and is connected to at least one of said perturbator bodies (23) in order to modify its position in said resonant cavity (19) and modify the resonance frequency of the latter.

2. Band-pass filter as in claim 1, characterized in that said mechanical actuation device (28) is configured to adjust at least the angular position of said perturbator body (23) with respect to an axis of rotation (X) transverse to said longitudinal axis (Z).

3. Band-pass filter as in claim 1 or 2, characterized in that said mechanical actuation device (28) is configured to move said perturbator body (23) linearly in the respective resonant cavity (19).

4. Band-pass filter as in claim 2 and 3, characterized in that said mechanical actuation device (28) is configured to move the at least one perturbator body (23) in a combined manner, both linear and rotating.

5. Band-pass filter as in any claim hereinbefore, characterized in that said at least one mechanical actuation device (28) is configured to make all or at least some of said perturbator bodies (23) rotate in a synchronized manner.

6. Band-pass filter as in any of the claims from 1 to 4, characterized in that each perturbator body (23) is connected to its own mechanical actuation device (28) in order to move it autonomously from the others.

7. Band-pass filter as in any claim hereinbefore, characterized in that said perturbator bodies (23) comprise a perturbator element (24) and at least one support shaft (25) configured to support the perturbator element (24) in said waveguide cavity (15).

8. Band-pass filter as in claim 7, characterized in that at least part of said support shaft (25) extends through, in a support seating (27) made in at least one of either said first body (11) or said second body (12), and has a free end located externally to the first body (11) and the second body (12) and connected to the mechanical actuation device (28).

9. Band-pass filter as in claim 7 or 8, characterized in that said perturbator element (24) has a symmetrical conformation with respect to at least one of its symmetrical axes and said support shaft (25) is configured to support said perturbator element (24) around said axis of symmetry.

10. Band-pass filter as in claim 7 or 8, characterized in that said support shaft (25) is configured to support said perturbator element (24) on a non-symmetrical axis of the perturbator element (24).

1 1. Band-pass filter as in any claim hereinbefore, characterized in that said waveguide cavity (15) has a substantially rectangular cross section shape.

12. Band-pass filter as in any claim hereinbefore, characterized in that said resonant cavities (19) are disposed aligned along said longitudinal axis Z.

13. Band-pass filter as in any claim hereinbefore, characterized in that said plate (16) has a length (LF), in a direction parallel to said longitudinal axis (Z), which is less than the length (LG) of the first body (11) and the second body (12).

14. Band-pass filter as in any claim hereinbefore, characterized in that said perturbator bodies (23), installed in said waveguide cavity (15), have the same shape and size.

15. Band-pass filter as in any claim hereinbefore, characterized in that said perturbator bodies (23) are installed in said waveguide cavity (15) aligned along said longitudinal axis (Z).

16. Band-pass filter as in any claim hereinbefore, characterized in that said perturbator bodies (23) are made of dielectric material.

17. Band-pass filter as in any of the claims from 1 to 15, characterized in that said perturbator bodies (23) are made of metal material.

18. Band-pass filter as in any of the claims from 1 to 15, characterized in that said perturbator bodies (23) are made of metal material and of dielectric material.

19. Circuit for microwave applications comprising at least a band-pass filter as in any claim hereinbefore.