Waffle iron filter assembly for high-frequency signals

Description

Technical field

[0001] This description relates to a filter arrangement for high-frequency signals (RF signals), which is used, for example, in communication equipment, particularly in conjunction with waveguides. Such communication equipment can be, for example, transmitting and / or receiving equipment. Technical background

[0002] Signal filters are used in communication devices to allow or suppress signal components in certain frequency ranges, so that essentially only the desired signal components appear at an output of the filter, and the unwanted signal components are removed or very strongly attenuated.

[0003] Signal filters are available in various designs and for diverse applications. For example, signal filters can be constructed with discrete electronic components such as inductors, capacitors, and semiconductors. Especially for high frequencies, such as several GHz and above, waveguides are used for signal processing and transmission. In conjunction with waveguides, corresponding filters are also used that do not require discrete electronic components.

[0004] For waveguide filters (or resonators) used at high frequencies (e.g., in the K-band, 18 to 27 GHz and above), the design and geometry of the waveguide and the filter are crucial for the filter's performance. Therefore, achieving high filter performance depends on the design, dimensions, and geometric configuration of the filter or resonator.

[0005] Guthart H: "A High-Power S-Band Filter (Correspondence)", IRE Transactions on Microwave Theory and Techniques, IEEE, USA, Vol. 6, No. 2, March 1, 1962, pages 148-149, describes a so-called waffle iron filter for the S-band. The filter consists of two hemispheres with a cavity between them. Within this cavity is a section with depressions and corresponding ridges. The dimensions of the depressions and ridges are matched to the wavelength of the signals being processed. The housing is made of highly conductive copper.

[0006] US 7,132,909 B2 describes various designs of waveguides, which generally have a rectangular cross-section. Geometrically differentiated elements are arranged within a cavity of the waveguide to influence the propagating field. A key aspect of this document is that the elements arranged within the cavity have different dimensions. The random distribution of these dimensional variations, through averaging, is intended to achieve higher accuracy and lower overall deviation than would be possible by manufacturing a waveguide without such additional elements.

[0007] MAAS SUSAN ET AL: "Multi-layered substrate integrated waveguide waffle-iron filters", IET MICROWAVES, ANTENNAS & PROPAGATION, THE INSTITUTION OF ENGINEERING AND TECHNOLOGY, UNITED KINGDOM, Vol. 14, No. 10, August 12, 2020, pages 1038-1046 describes a waffle-iron filter integrated into a multi-layer substrate with input and output transformer sections that are inserted into the rectangular waveguides of the components connected to the waffle-iron filter.

[0008] For example, DE 10 2012 020 576 A1 describes a filter for a waveguide with adjustable coupling resonators and a frequency resonator.

[0009] Another example of a high-frequency resonator can be found in DE 10 2016 107 955 A1. Here, the resonator is tuned by means of a container in which a liquid crystal is contained, whereby the container is at least partially enclosed in the resonator space. Description

[0010] The task can be considered to be to specify a high-frequency filter characterized by a wide stopband in which the filter does not allow any signals to pass through or whose attenuation is above a required attenuation level.

[0011] This problem is solved by the subject matter of the independent claim. Further embodiments are described in the dependent claims and in the following description.

[0012] According to a first aspect, a filter arrangement for high-frequency signals (HF signals) is specified. The filter arrangement comprises a housing and a waffle iron assembly. The housing contains a cavity extending longitudinally. The waffle iron assembly is arranged within the cavity and has a support plate. The support plate has a plurality of recesses, with an electrically conductive material arranged in at least some of the recesses to form a pin located in the recess. The housing cavity contains two transformer sections and one waffle iron section, the waffle iron section being arranged between the two transformer sections. The support plate is arranged within the waffle iron section. The support plate contains a material transparent to HF signals.

[0013] In one embodiment, the housing is designed as an integral component or formed from two half-shells.

[0014] For example, an integrally designed housing can be manufactured using 3D printing technology. Alternatively, the housing can be cast or manufactured using another production technique, so that the cavity is located inside the housing and is accessible from at least one side to insert the mounting plate and place it in its intended position.

[0015] Alternatively, the housing can have two half-shells, with the second half-shell being arranged on the first half-shell in an assembled state such that the cavity is located or formed between the first half-shell and the second half-shell.

[0016] The following description refers in detail to the variant of the housing consisting of two half-shells. However, those skilled in the art will understand that this reference is merely exemplary and that the description also applies to other variants of the housing, in particular to the one-piece variant, such as that which can be manufactured using 3D printing technology. The function of the support plate and its arrangement within the cavity of the housing are independent of whether the housing is designed as a single piece or in multiple parts.

[0017] The cavity between the first and second half-shells is channel-shaped and extends from one end face to the opposite end face in the longitudinal direction of the filter assembly or the half-shells, so that the cavity acts like a waveguide for RF signals. The cavity is narrower than the half-shells, meaning that the half-shells touch or abut each other next to the cavity when assembled (i.e., when the first and second half-shells are connected).

[0018] For example, the cavity is formed by milling or otherwise manufacturing a corresponding recess into the surfaces of the two half-shells that are opposite or adjacent to each other in the assembled state of the filter assembly, so that these recesses form the cavity running in the longitudinal direction of the filter assembly when the half-shells are mounted together with the surfaces provided for this purpose, e.g. screwed or clamped.

[0019] The waffle iron assembly is positioned within the cavity such that the cavity is divided into several sections along the longitudinal direction of the filter assembly. The waffle iron assembly is arranged such that on both sides of this cavity, along the longitudinal direction, there is a section between the waffle iron assembly and the respective end connections of the filter assembly. For example, the waffle iron assembly is positioned centrally along the longitudinal direction of the cavity, and the sections of the cavity on both sides of the waffle iron assembly are of equal length.

[0020] The cavity is thus divided into a waffle section and two transformer sections, with the waffle section located between the two transformer sections. Starting from a terminal or end face of the filter assembly, a transformer section is connected first, followed by the waffle section, and then by another transformer section extending to the opposite end face of the filter assembly. The two transformer sections can be mirror images of each other with respect to the waffle section.

[0021] The waffle iron arrangement serves to allow or suppress RF signals propagating within the cavity of the filter assembly. This is how the filter function is implemented.

[0022] The recesses in the carrier plate are designed, for example, as bores in the form of depressions or holes and extend in the carrier plate in such a way that the recesses run perpendicular to the longitudinal direction of the cavity. An electrically conductive material, which takes the form of pins, is arranged in the recesses. The pins then form the teeth of the waffle iron, realizing the filter function in the cavity due to their geometry and position.

[0023] The electrically conductive material can be introduced into the recesses in a liquid state, where it then hardens to form the pins that are held in position by the carrier plate.

[0024] The majority of the recesses in the carrier plate can be arranged at regular or irregular intervals in one or more rows. The carrier plate can have a large number of recesses, all or some of which are filled with electrically conductive material, for example, to achieve a desired filtering function. Thus, a carrier plate can be designed according to requirements by filling the desired recesses and the desired number of them with electrically conductive material. The carrier plate can also have recesses that are not filled with electrically conductive material, for example, to reduce or minimize the amount of carrier plate material located within the cavity of the filter assembly.

[0025] The hemispheres are made of an electrically conductive material, or contain such a material or a combination of such materials, such as aluminum, Invar, copper, or brass. The hemispheres may be coated (for example, with gold or silver) or chromated.

[0026] Typically, the teeth of a waffle iron filter become smaller the higher the signal frequencies it is intended to filter. If the signals to be processed are in the range of several gigahertz (GHz), for example in the K-band at around 20 GHz or above, then the teeth of the waffle iron filter must be very small.

[0027] The filter arrangement and the waffle iron arrangement, designed according to the principles described herein, allow the pins formed in the carrier plate to be manufactured with high precision at very small dimensions (down to a diameter or height of a few tenths or even hundredths of a millimeter), so that the waffle iron arrangement can also be used at high frequencies (starting at 20 GHz up to 100 GHz or above). Furthermore, the carrier plate also provides mechanical stability to the teeth because the teeth are held as pins in the recesses of the carrier plate.

[0028] The shape, position, and number of each pin are essentially a negative of the carrier plate with its recesses. The carrier plate is first manufactured as a circuit board with the corresponding recesses. Then, the material from which the pins are made is poured in liquid form into the recesses, where it hardens and remains. The carrier plate, together with the pins, then forms the waffle iron array and is used in the filter assembly. In this way, a waffle iron array suitable for very high frequencies (20 GHz or higher) can be provided because the pins of the waffle iron array can be manufactured and used with the required (sometimes very small) size and dimensions.

[0029] According to one embodiment, the recesses in the carrier plate extend over the entire thickness of the carrier plate, with a pin completely filling each recess.

[0030] The recesses are, for example, holes that extend between two opposing surfaces of the carrier plate.

[0031] Preferably, the pins should be flush with the surfaces of the carrier plate, i.e., the pins should not protrude from the carrier plate, but should still completely fill the recesses.

[0032] According to another embodiment, the pins contain an electrically conductive epoxy resin in the recesses.

[0033] The epoxy resin can, for example, be electroplated with copper.

[0034] According to another embodiment, at least some of the recesses in which the pins are arranged have a circular cross-section.

[0035] Accordingly, the pins also have a circular cross-section.

[0036] According to a further embodiment, a surface of the carrier plate, from which the recesses extend into the carrier plate, has a coating, wherein the coating comprises an electrically conductive material.

[0037] The coating thus forms a galvanic connection between the pins arranged in the recesses, so that the pins, as a unit, implement the filter function. All pins are galvanically connected to each other and, according to their shape, position, and arrangement, exert a filtering function on high-frequency signals transmitted through the cavity.

[0038] According to another embodiment, the waffle iron assembly is connected to the housing in such a way that the pins in the recesses are galvanically connected to the housing.

[0039] From a signal transmission perspective in the high-frequency range, the pins and the galvanically connected housing or half-shell form a single unit. This design has essentially the same effect on high-frequency signals transmitted through the cavity and intended to be filtered as if the pins were milled into the surface of the half-shell in the form of teeth.

[0040] The construction according to this embodiment can be implemented, for example, by bonding the surface of the carrier plate from which the recesses with the pins extend into the carrier plate to the first half-shell or the housing in an electrically conductive manner. Preferably, the aforementioned coating is located on this surface of the carrier plate, so that the carrier plate is electrically conductively bonded to the first half-shell or the housing at the surface of the coating.

[0041] The pins are connected to the housing or the first half-shell either directly or indirectly via galvanic connection. An example of an indirect galvanic connection is the connection made by bonding the coating to the housing or the first half-shell. An alternative example of a direct galvanic connection would be to individually bond the pins to the housing or the first half-shell with electrically conductive adhesive, for example, by applying a predetermined amount of adhesive to each pin and then pressing the carrier plate against a surface of the cavity in the housing or a surface of the first half-shell, thus bonding it in place.

[0042] According to another embodiment, the waffle iron assembly is bonded to the housing by means of an adhesive layer having an electrically conductive adhesive.

[0043] For example, an epoxy adhesive or a silicone adhesive that vulcanizes at room temperature can be used as an adhesive.

[0044] The substrate contains a material that is transparent to RF signals. For example, the substrate is a printed circuit board that is transparent to RF signals.

[0045] The base plate is made of high-quality, RF-compatible circuit board material, such as reinforced Teflon. The base plate is a dielectric characterized by low dielectric losses and high transmittance for RF signals. Such high-quality materials have low losses, thus converting less RF energy into heat, and ideally, their dielectric properties closely resemble those of a vacuum. This allows the waffle iron assembly to fulfill its filtering function for RF signals, as the RF signals pass through the material without any significant impact, and the waffle iron can exert its own inherent influence on the RF signals.The carrier plate surrounds the teeth of the waffle iron assembly and protects the waffle iron itself and the pins made of electrically conductive material from external mechanical stresses, which is particularly advantageous for teeth of a waffle iron filter with very small dimensions for high frequencies.

[0046] According to a further embodiment, the filter assembly also includes a second waffle iron assembly, which is connected to the housing. The second waffle iron assembly is located opposite the first waffle iron assembly and is spaced apart from the first waffle iron assembly at a predetermined distance.

[0047] The same applies to the design of the second waffle iron assembly as was explained above with regard to the (first) waffle iron assembly. The explanations given there apply analogously to the second waffle iron assembly and are not repeated here. Likewise, the same applies to the connection between the second waffle iron assembly and the housing or the second half-shell as was explained with regard to the connection between the (first) waffle iron assembly and the housing or the first half-shell. In any case, the two waffle iron assemblies are attached to opposite surfaces of the housing cavity, which applies to both a one-piece housing and a housing consisting of two (or more) half-shells.

[0048] The combination of the first and second waffle iron arrangements realizes the filter function in the cavity between the two half-shells, with a transformer section located between the combination of the two waffle iron arrangements and each of the two opposite end faces of the filter arrangement.

[0049] According to another embodiment, the pins of the waffle iron arrangement extend towards the second waffle iron arrangement.

[0050] The filter arrangement as described herein can be used, for example, in signal processing units or signal transmission units in communication equipment, such as communication satellites or other components of signal transmission links.

[0051] The filter arrangement described here enables a high degree of miniaturization of waffle iron filters and thus their use for very high frequencies. Brief description of the characters

[0052] The following section describes exemplary embodiments with reference to the accompanying drawings. The illustrations are schematic and not to scale. Identical reference numerals refer to identical or similar elements. The drawings show: Fig. 1 A schematic representation of part of a waffle iron filter. Fig. 2 A schematic representation of a half-shell of a filter arrangement according to an exemplary embodiment. Fig. 3 a schematic representation of the cavity and two waffle iron arrangements of a filter arrangement according to a further embodiment. Fig. 4 a schematic representation of two waffle iron arrangements of a filter arrangement according to a further embodiment. Fig. 5 a schematic representation of two half-shells of a filter arrangement according to a further embodiment. Fig. 6 a schematic representation of the pins and the coating of a waffle iron arrangement for a filter arrangement according to a further embodiment. Fig. 7 a schematic representation of a half-shell with adhesive layer and waffle iron arrangement for a filter arrangement according to a further embodiment. Detailed description of implementation examples

[0053] Fig. 1 Figure 1 schematically shows the typical structure of a half-shell 20 of a filter arrangement 10 in a waffle-iron structure. A filter arrangement usually consists of two such half-shells 20, which are joined together at the surface facing the viewer, so that a cavity (or two such cavities 18, as shown in Figure 1) exists between the half-shells. Fig. 1 shown, extending from bottom to top) and forming a waffle iron structure.

[0054] The half-shell 20 has a first connection 11 (the top end in the illustration) and a second connection 12 (the bottom end in the illustration). An external waveguide is connected to these connections 11 and 12, but this waveguide is... Fig. 1 not shown. Connections 11 and 12 each have a flange 13 to which a waveguide can be connected.

[0055] Starting from the first terminal 11 and the second terminal 12, a cavity (or two cavities) extends towards the waffle-shaped section 15, with the cavity 18 forming a transformer section 14 on both sides of the waffle-shaped section 15. The waffle-shaped section 15 has a plurality of teeth 16. The dimensions of the teeth 16 decrease as the frequency of the signals to be processed increases. In the example of the Fig. 1 The teeth and the entire structure of the half-shell are milled into a metal block. However, as the size of the teeth 16 decreases, higher demands are placed on the manufacturing of the tooth structure in the waffle section 15, because at very high frequencies the teeth can have cross-sections of a few tenths or hundredths of a square millimeter.

[0056] Along the half-shell 20 several recesses 17 are arranged, which make it possible to assemble the two half-shells, for example by inserting and fastening screws 17 into these recesses.

[0057] The transformer section 14 has a cross-section that tapers from the end faces towards the waffle section 15.

[0058] In light of this general description of a waffle iron filter structure of the Fig. 1 will now be discussed in relation to the Fig. 2 bis 7 Alternative structures of a filter arrangement are described.

[0059] Fig. 2 Figure 1 shows a schematic representation of a half-shell 20. Two mountings 19 are arranged on each of the end faces, left and right, to connect an external waveguide (not shown) to the filter assembly. In this example, the mountings are threaded holes. However, it is of course possible to choose other mounting methods, such as clamp connections or other suitable connection types.

[0060] The cavity 18 extends centrally in the half-shell from left to right, starting from the first connection 11 and towards the second connection 12, initially forming a transformer section 14, with this transformer section leading into the waffle section 15, to which another transformer section is connected.

[0061] The transformer sections 14 are designed such that their cross-section decreases from the respective end face to the waffle-shaped section 15. This is achieved in this case by decreasing the depth of the cavity as one approaches the waffle-shaped section 15. In the example of the Fig. 2 Several steps are arranged for this purpose, their height increasing the closer they are to the waffle-shaped section 15. This change in cross-section already filters out some signal components.

[0062] In the waffle section 15 a waffle iron arrangement 100 is arranged and electrically connected to the half-shell, namely at the underside of the waffle iron arrangement 100.

[0063] Fig. 3 Figure 1 shows a detailed representation of the cavity 18 (shown here as a negative without the surrounding half-shells) and two waffle iron assemblies 100 and 200. The cavities 18 located on both sides of the waffle iron assemblies 100 and 200 have a tapered cross-section extending from the first connection 11 and the second connection 12, respectively, towards the waffle iron assemblies 100 and 200. The transformer sections 14 of the cavity 18 can be identical in terms of their dimensions and shape.

[0064] Between the transformer sections 14, the waffle section 15 with two waffle iron assemblies 100, 200 is arranged. The waffle iron assemblies are each electrically connected by a half-shell and are spaced apart from each other.

[0065] Fig. 4 shows a detailed representation of the two waffle iron arrangements 100, 200 from Fig. 3 Each waffle iron arrangement 100, 200 has a support plate 102, 202 with a corresponding plate thickness 120, 220. It can be seen that the two waffle iron arrangements 100, 200 do not touch each other, but are positioned at a predetermined distance from one another, so that the cavity 18 extends between them. The first waffle iron arrangement 100 is described here, with the second waffle iron arrangement having a similar construction.

[0066] The waffle arrangement 100 has a carrier plate 102, which can be, for example, a printed circuit board (PCB). The carrier plate can have side lengths of a few millimeters. Several recesses 115 are arranged in the carrier plate 102, extending over the entire plate thickness 120 from one surface 105 to the opposite surface at the cavity 18. An electrically conductive material is inserted into the recesses 115 to form the teeth of the waffle iron filter.

[0067] Surface 105 of the carrier plate 102 is the surface that is attached to the half-shell. In this example, surface 105 is metallically coated, with the coating 110 shown as hatching to reveal the structure of the carrier plate 102 with its recesses 115. The coating 110 thus represents a metallic plane on surface 105 of the carrier plate 102. The coating 110 is galvanically bonded to the teeth in the recesses 115.

[0068] It should be noted that the number and arrangement of the cutouts in the illustration of the Fig. 4 This is merely an example. Both the number and the arrangement of the cutouts can be freely selected depending on the required filter properties of the filter arrangement.

[0069] Fig. 5 Figure 1 shows a schematic representation of the first half-shell 20 and the second half-shell 25 in an unassembled state of the filter assembly. The first waffle iron assembly 100 is located centrally in the first half-shell 20, and the second waffle iron assembly 200 is located centrally in the second half-shell 25, so that the two waffle iron assemblies are opposite each other when the second half-shell 25 is assembled with the first half-shell 20. The cavity 18 extends along the half-shells 20 and 25 in the longitudinal direction 40.

[0070] Fig. 6 Figure 1 shows a schematic representation of the metallic coating 100 and the pins 112 of the waffle iron assembly 100. This is the negative of the carrier plate 102, wherein in Fig. 6 For the sake of illustration and simplification, only four pins 112 are shown. The coating 110 forms a continuous, planar element along the surface 105. The pins 112 adjoin the coating and extend perpendicularly to it. Accordingly, the recesses 115 also extend perpendicularly to the surface 105.

[0071] Fig. 7 Figure 1 schematically shows the connection between half-shell 20, adhesive layer 30, and waffle iron assembly 100. The remaining structure of the half-shell is not shown here. In any case, the waffle iron assembly 100 is electrically bonded to half-shell 20 by means of an adhesive layer 30, specifically at the point indicated in Fig. 2 forms waffle section 15.

[0072] The filter arrangement 10 as described herein enables the use of the waffle iron filter structure for high frequencies at 20 GHz and above.

[0073] Waffle iron filters, used as low-pass filters, have advantageous properties because they have a very high recurrence frequency at which they become transparent again to high-frequency signals. A disadvantage of conventional waffle iron filters, such as those in... Fig. 1 However, it has been shown that they are difficult to manufacture for high frequencies because the tooth structure cannot be produced in the required geometries for high frequencies. With the design described here, however, it is easy to offer a waffle iron filter even for frequencies in the RF range, because this design allows for a particularly precise and miniaturized waffle iron arrangement. Reference symbol list

[0074] 10 Filter assembly, waffle iron filter 11 First connection 12 Second connection 13 Flange 14 Transformer section 15 Waffle section 16 Tooth 17 Recess 18 Cavity 19 Fastening 20 First half shell 25 Second half shell 30 Adhesive layer 40 Longitudinal direction 100 Waffle iron assembly 102 Support plate 105 Surface 110 Coating 112 Pin 115 Recess 120 Plate thickness 200 Waffle iron assembly 202 Support plate 220 Plate thickness

Claims

1. A filter assembly (10) for high-frequency signals, HF-signals, comprising: a housing (20, 25) having a cavity (18) therein extending in a longitudinal direction (40) of the housing (20, 25); a waffle iron assembly (100) disposed in the cavity (18); the waffle iron assembly (100) comprising: a carrier plate (102) having a plurality of recesses (115); wherein an electrically conductive material is disposed in at least some of the recesses (115), the electrically conductive material each forming a pin (112) in the at least some of the recesses (115); wherein the cavity (18) of the housing (20, 25) includes two transformer sections (14) and a waffle section (15), the waffle section (15) being disposed between the two transformer sections (14); wherein the carrier plate (102) is disposed in the waffle section (15); wherein the carrier plate (102) includes a material permeable to HF signals.

2. The filter assembly (10) of claim 1, wherein the recesses (115) in the carrier plate (102) extend across an entire plate thickness (120) of the carrier plate (102); wherein a pin (112) completely fills the respective recess (115).

3. The filter assembly (10) of claim 1 or 2, wherein the pins (112) in the recesses (115) contain an electrically conductive epoxy resin.

4. The filter assembly (10) of one of the preceding claims, wherein at least some of the recesses (115) in which the pins (112) are disposed have a circular cross-section.

5. The filter assembly (10) of one of the preceding claims, wherein a surface (105) of the carrier plate (102) from which the recesses (115) extend into the carrier plate comprises a coating (110); wherein the coating (110) comprises an electrically conductive material.

6. The filter assembly (10) of one of the preceding claims, wherein the waffle iron assembly (100) is connected to the housing such that the pins (112) in the recesses (115) are galvanically connected to the housing.

7. The filter assembly (10) of one of the preceding claims, wherein the waffle iron assembly (100) is bonded to the housing by means of an adhesive layer (30) comprising an electrically conductive adhesive.

8. The filter assembly (10) of one of the preceding claims, wherein the carrier plate is a circuit board permeable to HF signals.

9. The filter assembly (10) of one of the preceding claims, further comprising a second waffle iron assembly (200) which is connected to the housing; wherein the second waffle iron assembly (200) is opposite the first waffle iron assembly (100) and is spaced apart from the first waffle iron assembly (100) at a predetermined distance.

10. The filter assembly (10) of claim 9, wherein the pins (112) of the waffle iron assembly (100) extend towards the second waffle iron assembly (200).

11. The filter assembly (10) of one of the preceding claims, wherein the housing is an integral housing or consists of two half-shells (20, 25).