Multi-band filter and an antenna system comprising a multi-band filter

Abstract

The invention concerns a multi-band filter (1). The multi-band filter (1) comprises a housing (2) and a planar filter structure (5), wherein the housing is adjusted to cover the filter structure (5), and wherein the planar filter structure (5) comprises an input port (3) and an output port (4) and comprises structures that are forming an input filter (6), wherein a first side of the input filter is coupled to the input port (3), wherein the input filter (6) is a band-stop filter or a lowpass filter, an output filter (7), wherein a first side of the output filter (7) is coupled to the output port (4), wherein the output filter (7) is a band-stop filter or a lowpass filter, and at least two bandpass filters (8, 9), wherein the bandpass filters (8, 9) are connected in parallel in between a second side of the input filter (6) and a second side of the output filter (7).

Description

[0001] Multi-band filter and an Antenna system comprising a multi-band filter

[0002] Technical field

[0003] The invention refers to a multi-band filter and an antenna system comprising a multi-band filter.

[0004] Background

[0005] Small and compact filters are required for active antenna systems (AAS). This includes multiband filters that are commonly used in such active antenna systems.

[0006] Multi-band filters according to the art often or require a complex tuning of the filter, which implies that multiple tuning elements for tuning the resonancy frequency of each individual resonator and the mutual coupling between these resonators are provided for the respective filter.

[0007] It is further known in the art that combline filters can be formed on printed circuit boards. For example, GB2359667A discloses a combline filter that is formed by a conductive structure on a printed circuit board.

[0008] However, when it comes to the realization of multi-band filters, it is a challenge to combine the required filter structures in a single housing.

[0009] Summary

[0010] A multi-band filter according to the invention comprises a housing and a planar filter structure, wherein the housing is adjusted to cover the filter structure, and wherein the filter structure comprises an input port and an output port and comprises structures that are forming an input filter, wherein a first side of the input filter is coupled to the input port, wherein the input filter is a band-stop filter or a lowpass filter, an output filter, wherein a first side of the output filter is coupled to the output port, wherein the output filter is a band-stop filter or a lowpass filter, and at least two bandpass filters, wherein the bandpass filters are connected in parallel in between a second side of the input filter and a second side of the output filter.

[0011] The multi-band filter is preferably a dual-band filter.

[0012] The filter structure is covered by the housing. Optionally, the entire filter structure is inside the housing. In the alternative, only parts of the filter structure are covered by the housing, wherein at least the input filter, the output filter and the bandpass filters are covered by the housing. This means that the input filter, the output filter and the bandpass filters are all aligned inside a single housing.

[0013] The planar filter structure is a structure that has the shape of a plate. This means that the planar filter structure essentially extends in a plane. Optionally, the planar filter structure comprises multiple layers. The filter structure comprises elements that are configured to provide the filter characteristics of the input filter, the output filter and the bandpass filters. The filter structure preferably comprises only passive electronic components.

[0014] The filter structure comprises an input port and an output port. The input port is configured to receive an input signal and the output port is configured to provide an output signal. The output signal is the filtered input signal. The input port is optionally connected to an input connector or is connected to a suitable interface. The output port is optionally connected to an output connector. The input connector and the output connector are preferably mounted to the housing, which allows a connection of external components to the filter structure.

[0015] The input filter is a band-stop filter or a lowpass filter. The input filter is preferably designed to suppress frequencies that are above the frequencies of the passbands of the bandpass filters. This means that the passband of the input filter is overlapping with the passband of the bandpass filters. The output filter is a band-stop filter or a lowpass filter. The output filter is preferably designed to suppress frequencies that are above the frequencies of the passbands of the bandpass filters. This means that the passband of the output filter is overlapping with the passband of the bandpass filters. The input filter and the output filter are preferably designed to provide the same pass-band.

[0016] The first side of the input filter is coupled to the input port and the first side of the output filter is coupled to the output port. The bandpass filters are connected in parallel in between a second side of the input filter and a second side of the output filter. The first side of the input filter is an input side of the input filter. The second side of the input filter is an output side of the input filter. The first side of the output filter is an output side of the output filter. The second side of the output filter is an input side of the output filter. Therefore, the bandpass filters are both connected with their respective input side to the output side of the input filter. Also, the bandpass filters are both connected with their respective output side to the input side of the output filter. For completeness, it is noted that the output side of a filter can also be understood as an input side of this filter, depending on the port that is used to provide a signal to the multi-band filter.

[0017] Generally speaking, resonance modes, so called box modes, can be caused by signals that are applied to the filter structure that is covered by a housing. Any additional filter that is inside the housing can lead to further resonance modes. When designing a multi-band filter, it has to be considered that bandpass filters that are used for defining the passbands of the multi-band filter might not have a sufficient attenuation in the stop-band or in parts of the stop-band. Therefore, it is preferable that an additional band-stop filter or a lowpass filter is incorporated to such a filter structure, which has been done according to the invention. It has been shown that adding a single band-stop filter or a lowpass filter on the input side or the output side of the filter structure leads to increased box modes due to a one-sided stimulation of the resonance modes. According to the invention, this is overcome by aligning two band-stop filters on the input side and the output side of the filter structure, respectively. Same effect is achieved by aligning two lowpass filters on the input side and the output side of the filter structure, respectively. Also a use of a band-stop filter in combination with a lowpass filter of different sides of the filter structure can be applied. In all cases, the resonance modes that are caused inside the housing and that are stimulated by the band-stop filters or the lowpass filters are suitable to compensate or erase each other.

[0018] The dependent claims define preferable embodiments of the invention.

[0019] Preferably, the bandpass filters are combline filters. A combline filter is a filter that is designed using combline technique. Preferably, the bandpass filters are stripline or micro-stripline combline filters. A combline filter preferably comprises a plurality of resonator elements that are extending in parallel. Optionally, the resonator elements extend from a common connection line. Preferably, the bandpass filters are combline filters with inductive inverters, which is providing additional freedom for adjusting a geometrical length of the two bandpass filters. This can be used for minimizing parasitic effects that are caused at a connection point of the bandpass filters, that is where a signal path splits after the input filter or is combined before the output filter, for each one of the bandpass filters by the respective neighbouring bandpass filter.

[0020] Preferably, the input filter is a combline filter and / or the output filter is a combline filter. Preferably, the input filter and / or the output filter is a stripline combline filter or a micorstripline filter. A combline filter preferably comprises a plurality of resonator elements that are extending in parallel. Optionally, the resonator elements extend from a common connection line.

[0021] Preferably, the input filter comprises a plurality of input filter resonators, wherein a shielding-element is aligned in and / or above the filter structure between two of the input filter resonators. The input filter resonators are preferably extending in a common plane. The shielding-element is aligned in and / or above the common plane. The shielding-element is preferably aligned above the filter structure and between the two of the input filter resonators. This is the case when a projection of the shielding-element is between the two of the input filter resonators, wherein the projection is perpendicular to the surface of the common plane. A shielding element is a conductive element that is capable to suppress the propagation of electromagnetic waves.

[0022] A shielding-element can be a conductive area that is aligned in the layer that is formed by the planar filter structure. For example, the input filter resonators are conductors on a printed circuit board and the shielding-element is a grounded conductor on the printed circuit board that extends in between two of the input filter resonators. A shielding-element can be a conductive area that is aligned above the layer that is formed by the planar filter structure. For example, the input filter resonators are conductors on a printed circuit board and the shielding-element is a grounded conductor that is aligned on top of the printed circuit board.

[0023] Preferably, multiple shielding-elements are aligned in and / or above the filter structure between different pairs of adjacent input filter resonators. Each shielding-element is providing a shielding on one side of an input filter resonator. Therefore, a propagation of an electromagnetic wave that is stimulated by the respective input filter resonator is reduced and box modes that are caused by the respective input filter resonator can be minimized or eliminated. In particular, the use of multiple shielding-elements that are aligned in between different input filter resonators is suitable to avoid an occurrence of box modes and allows that a propagation of electromagnetic waves towards the input port is reduced. The shielding element is preferably grounded via the housing.

[0024] Preferably, the output filter comprises a plurality of output filter resonators, wherein a shieldingelement is aligned in and / or above the filter structure between two of the output filter resonators. The output filter resonators are preferably extending in a common plane, which is preferably the same common plane in which the input filter resonators are aligned. The shielding-element is aligned in and / or above the common plane. The shielding-element is preferably aligned above the filter structure and between the two of the output filter resonators. This is the case when a projection of the shielding-element is between the two of the input filter resonators, wherein the projection is perpendicular to the surface of the common plane. A shielding element is a conductive element that is capable to suppress the propagation of electromagnetic waves.

[0025] A shielding-element can be a conductive area that is aligned in the layer that is formed by the planar filter structure. For example, the output filter resonators are conductors on a printed circuit board and the shielding-element is a grounded conductor on the printed circuit board that extends in between two of the output filter resonators. A shielding-element can be a conductive area that is aligned above the layer that is formed by the planar filter structure. For example, the output filter resonators are conductors on a printed circuit board and the shielding-element is a grounded conductor that is aligned on top of the printed circuit board. Preferably, multiple shielding-elements are aligned in and / or above the filter structure between different pairs of adjacent output filter resonators. Each shielding-element is providing a shielding on one side of an output filter resonator. Therefore, a propagation of an electromagnetic wave that is stimulated by the respective output filter resonator is reduced and box modes that are caused by the respective input filter resonator can be minimized or eliminated. In particular, the use of multiple shielding-elements that are aligned in between different output filter resonators is suitable to avoid an occurrence of box modes and allows that a propagation of electromagnetic waves towards the output port is reduced. The shielding element is preferably grounded via the housing.

[0026] As the input filter is forming a band-stop filter or a lowpass filter, a propagation of higher modes of the filter as such can be avoided. However, this does not necessarily affect a propagation of box modes inside the housing. Both effects can be undesired but have different causes. Therefore, to minimize undesired effects, a combination of a band-stop filter or a lowpass filter as input filter and the shielding-element in between the input filter resonators is advantageous. Accordingly, also a combination of a band-stop filter or a lowpass filter as output filter and the shielding-element in between the output filter resonators is advantageous.

[0027] Preferably, the filter structure is a printed circuit board, PCB. The use of a PCB allows a very precise manufacturing in respect to the size and the position of the filter resonators of the input filter, the output filter and / or the bandpass filters. Due to the high precision that can be achieved in manufacturing the filter structure on a PCB by etching, in combination with the limitation of unwanted box modes, it is optionally possible to provide a dual-band filter that does not comprise any tuning elements.

[0028] Preferably, the input filter, the output filter and the bandpass filters are formed on a first side of the PCB and a grounding layer is formed on a second side of the PCB, wherein the first side is a opposite side of the second side, wherein the input filter, the output filter and / or the bandpass filters comprises a grounding connection that is provided by a via in the PCB. Preferably, the filter structure comprises vias for providing a contact to the grounding layer. Due to the manufacturing techniques for PCBs, these vias can be positioned very accurately, which allows that desired filter parameters, for example filter bands that are defined by the bandpass filters, can be achieved very accurately.

[0029] Preferably, a conductive separator is aligned in and / or above the filter structure in between the at least two bandpass filters. The two bandpass filters are preferably extending in a common plane, which is preferably the same common plane in which the input filter resonators and / or the output filter resonators are aligned. The conductive separator is aligned in and / or above the common plane. The conductive separator is preferably aligned above the filter structure and between the at least two bandpass filters. This is the case when a projection of the conductive separator is between two of the input filter resonators, wherein the projection is perpendicular to the surface of the common plane. The conductive separator is providing a barrier for electromagnetic waves between the resonators of different bandpass filter, which allows a close mounting distance between the bandpass filters and avoids that the resonators of one bandpass filter are excited by electromagnetic waves that are emitted by the resonators of the other bandpass filter. The conductive separator is preferably grounded via the housing.

[0030] Preferably, the housing comprises a lid that comprises a cavity, wherein the input filter, the output filter and the at least two bandpass filters are aligned in or below the cavity. The cavity is forming a closed space above the filter structure such that any box modes that would be stimulated by the input filter, the output filter and / or the at least two bandpass filters are defined by the dimension of the cavity. This allows to form the cavity in such a way that box modes are minimized.

[0031] Preferably, the housing comprises three areas that are subsequently aligned in a first direction, the first direction being defined as a direction from the input port to the output port, wherein a first area is on the side of the input port, a second area is on a side of the output port and a third area is in between the first area and the second area in the first direction, wherein the input filter is aligned in the first area, the output filter is aligned in the second area, and the at least two bandpass filters are aligned in the third area, wherein the bandpass filters are both extending in parallel to each other and parallel to the first direction. The areas are not necessary physically separated areas but can be formed by a logical separation of the space inside the housing.

[0032] Preferably, an absorber element is aligned inside the housing in the third area. The absorber element is preferably aligned in between the filter structure and the housing. The absorber element is suitable to absorb or damp a propagation of electromagnetic waves. The absorber element might increase transmission losses in the multi-band filter but can be used to achieve the desired characteristics of a stop-band, for example to achieve a 80dB attenuation in an exemplary stop-band.

[0033] Preferably, the height of the housing above the input filter is different to the height of the housing above at least one of the bandpass filters. Preferably, a height of the housing above the output filter is different to a height of the housing above at least one of the bandpass filters. The height is a distance in a direction perpendicular to the plane in which the filter structure extends. The height is an inside height of the housing over the filter structure. In particular, the cavity of the housing has a different height in different areas, in particular a different height in the first area and in the third area or a different height in the second area and in the third area. The height of the cavity in the different areas is adjusted for the different resonance frequencies of the different filters that are aligned in the different areas, respectively.

[0034] Furthermore preferable, the housing comprises a bottom portion. Optionally the bottom portion comprises a top surface and the filter structure is aligned on the top surface, wherein the lid is aligned on the filter structure. In other words, the filter structure is optionally sandwiched in between the bottom portion and the lid of the housing. In this case it is preferable that multiple grounding vias are aligned at an outer circumference of the filter structure to avoid that electromagnetic waves are propagating to an outside of the housing through the filter structure. In the alternative, the filter structure is entirely enclosed by the housing.

[0035] Preferably, the dual-band filter comprises at least one tuning element that is extending from an outside of the housing to an inside of the housing. Although the multi-pass filter is capable to be operational without any tuning, as any undesired parasitic effects are widely eliminated, adding a tuning element can be advantageous to achieve even higher precision in the filter characteristics. That is, the filter characteristics can be adjusted to meet predetermined filter characteristics more specifically.

[0036] Preferably, the dual-band filter is configured to provide a first passband and a second passband, wherein the first passband is preferably located between 6Ghz and 7Ghz, and wherein the second passband is located between 7Ghz and 8Ghz.

[0037] Preferably, the input filter and the output filter both comprise a same number of filter resonators. Thus, a symmetric structure can be achieved and electromagnetic waves that are caused by the input filter and the output filter can eliminate each other.

[0038] Preferably, an antenna system comprises the dual-band filter according to the invention. Such antenna system has all advantages that are achieved by the dual-band filter according to the invention and can achieve a high signal quality in a transmitter or receiver path. Brief description of the drawings

[0039] Fig. 1 shows a view of a multi-band filter according to a first embodiment of the invention, fig. 2 shows a view of a filter structure of the multi-band filter according to the first embodiment of the invention, fig. 3 shows details in respect to an alignment of a housing above the filter structure of the multi-band filter according to the first embodiment of the invention, fig. 4 shows a view of the housing of the multi-band filter according to the first embodiment of the invention, fig. 5 shows a view of a housing of the multi-band filter according to a second embodiment of the invention, fig. 6 shows an antenna system according to the invention, and fig. 7 shows a diagram that is illustrating exemplary filter characteristics of a multi-band filter according to the first or second embodiment of the invention.

[0040] Detailed

[0041] Figure 1 is depicting a view of a multi-band filter 1 according to a first embodiment of the invention. The multi-band filter 1 is a dual-band filter.

[0042] The multi-band filter 1 comprises a housing 2 and a filter structure 5. The housing comprises a bottom portion 2a and a lid 2b, wherein the lid 2b is not shown in figure 1.

[0043] The filter structure 5 has a plate shape and is therefore a planar filter structure. The filter structure 5 comprises structures that are forming an input filter 6, an output filter 7, a first bandpass filter 8 and a second bandpass filter 9. The input filter 6 is a band-stop filter or a lowpass filter. The output filter 7 is a band-stop filter or a lowpass filter. In this embodiment, the filter structure 5 is a is a printed circuit board, PCB. The structures that are forming the filters 6, 7, 8, 9 comprise conductive elements that are arranged on the PCB. The input filter 6, the output filter 7 and the bandpass filters 8, 9 are combline filters. An input connector 16, for example a coaxial connector, is mounted on a first side of the bottom portion 2a of the housing 2. An output connector 17, for example a coaxial connector, is mounted on a second side of the bottom portion 2a of the housing 2. The first side of the bottom portion 2a and the second side of the bottom portion 2a are opposite sidewalls of the bottom portion 2a of the housing 2. The filter structure 5 is aligned in between the first side of the bottom portion 2a and the second side of the bottom portion 2a.

[0044] The bottom portion 2a of the housing 2 further comprises a ground plate that is connecting the first side of the bottom portion 2a and the second side of the bottom portion 2a. The filter structure 5 is aligned on the ground plate. The PCB that is forming the filter structure 5 comprises a plurality of through holes and a corresponding number of pins 15 is aligned on the ground plate. The pins extend through the of through holes for holding the filter structure 5. The pins can be screws that are mounted through the ground plate.

[0045] A first side of the input filter 6 is coupled to an input port 3, wherein the input port 3 is coupled to the input connector 16. The first side of the input filter 6 is an input side of the input filter 6. A second side of the input filter 6 is coupled to both of a first side of the first bandpass filter 8 and a first side of the second bandpass filter 9. The first side of the of the first bandpass filter 8 is an input side of the first bandpass filter 8. The first side of the of the second bandpass filter 9 is an input side of the second bandpass filter 9.

[0046] A first side of the output filter 7 is coupled to an output port 4, wherein the output port 4 is coupled to the output connector 17. The first side of the output filter 7 is an output side of the output filter 7. A second side of the output filter 7 is coupled to both of a second side of the first bandpass filter 8 and a second side of the second bandpass filter 9. The second side of the of the first bandpass filter 8 is an output side of the first bandpass filter 8. The second side of the of the second bandpass filter 9 is an output side of the second bandpass filter 9. Consequently, the two bandpass filters 8, 9 are connected in parallel in between a second side of the input filter 6 and a second side of the output filter 7.

[0047] Figure 2 shows a view of the filter structure 5 of the multi-band filter 1 according to the first embodiment of the invention. The input filter 6, the output filter 7 and the bandpass filters 8, 9 are formed on a first side of the PCB, which is also referred to as a top side of the PCB, and are visible in Figure 2. A grounding layer is formed on a second side of the PCB, which cannot be seen in Figure 2. The second side is a opposite side of the first side, which is also referred to as a bottom side of the PCB, and is not visible in Figure 2. The input filter 6, the output filter 7 and / or the bandpass filters 8, 9 comprises a grounding connection that is provided by multiple vias, for example a via 18, in the PCB. The input filter 6 comprises a plurality of input filter resonators 6a, 6b, 6c, 6d. In particular, the input filter 6 comprises a central line that is connecting the input port 3 with the input side of the bandpass filters 8, 9. The input filter resonators 6a, 6b, 6c, 6d are extending perpendicularly from the central line of the input filter 6. The input filter resonators 6a, 6b, 6c, 6d are aligned in two parallel rows on different sides of the central line of the input filter 6. In the depicted exemplary embodiment, a first input filter resonator 6a and a third input filter resonator 6c are extending to one side of the central line of the input filter 6. A second input filter resonator 6b and a fourth input filter resonator 6d are extending to the other side of the central line of the input filter 6.

[0048] Multiple shielding elements are aligned above the filter structure 5 in between the single input filter resonators 6a, 6b, 6c, 6d of the input filter 6. An exemplary shielding element of the multiple shielding elements is described by referring to a first shielding-element 11. The first shielding-element 11 is aligned above the filter structure 5 between two of the input filter resonators 6a, 6b, 6c, 6d. The first shielding element 11 is a portion of the lid 2b and is aligned such that the first shielding element 11 is positioned directly above the filter structure 5 and is positioned over the filter structure 5 such that the shielding-element 11 is in between two of the input filter resonators 6a, 6b, 6c, 6d, in the example of the first shielding element 11 in between the first input filter resonator 6a and the third input filter resonator 6c.

[0049] The lid 2 comprises multiple shielding elements that correspond to the input filter 6. This includes a shielding-element that is aligned above the filter structure 5 and between the second input filter resonator 6b and the fourth input filter resonator 6d. Further shielding-elements are aligned above the filter structure 5 at the input sided end and the output sided end of the input filter such that each one of the input filter resonators 6a, 6b, 6c, 6d is in between two shieldingelement. The shielding elements that are aligned above the filter structure 5 are aligned in a way that each input filter resonator 6a, 6b, 6c, 6d is in between two of the shielding elements when viewing a row of input filter resonators 6a, 6b, 6c, 6d of the input filter 6.

[0050] The output filter 7 comprises a plurality of output filter resonators 7a, 7b, 7c, 7d. In particular, the output filter 7 comprises a central line that is connecting the output side of the bandpass filters 8, 9 with the output port 4. The output filter resonators 7a, 7b, 7c, 7d are extending perpendicularly from the central line of the output filter 7. The number of output filter resonators 7a, 7b, 7c, 7d is identical to the number of input filter resonators 6a, 6b, 6c, 6d. The output filter resonators 7a, 7b, 7c, 7d are aligned in parallel in two rows on different sides of the central line of the output filter 7. In the depicted exemplary embodiment, a first output filter resonator 7a and a third output filter resonator 7c are extending to one side of the central connection line of the output filter 7. A second output filter resonator 7b and a fourth output filter resonator 7d are extending to the other side of the central connection line of the output filter 7.

[0051] Multiple shielding elements are aligned above the filter structure 5 in between the single output filter resonators 7a, 7b, 7c, 7d of the output filter 7. An exemplary shielding element of the multiple shielding elements is described by referring to a second shielding element 12. The second shielding element 12 is aligned above the filter structure 5 between two of the output filter resonators 7a, 7b, 7c, 7d. The second shielding element 12 is a portion of the lid 2b and is aligned such that the second shielding element 12 is positioned directly above the filter structure 5 and is positioned over the filter structure 5 such that the second shielding element 12 is in between two of the output filter resonators 7a, 7b, 7c, 7d, in the example of the second shielding element 12 in between the first output filter resonator 7a and the third output filter resonator 7c.

[0052] The lid 2 comprises multiple shielding elements that correspond to the output filter 7. This includes a shielding element that is aligned above the filter structure 5 and between the second output filter resonator 7b and the fourth output filter resonator 7d. Further shielding elements that are aligned above the filter structure 5 at the input sided end and the output sided end of the output filter 7 such that each one of the output filter resonators 7a, 7b, 7c, 7d is in between two shielding-elements. The shielding elements that are aligned above the filter structure 5 are aligned in a way that each output filter resonator 7a, 7b, 7c, 7d is in between two of the shielding elements when viewing a row of output filter resonators 7a, 7b, 7c, 7d of the output filter 7.

[0053] The first bandpass filter 8 comprises a plurality of first bandpass filter resonators, wherein the first bandpass filter resonators are aligned in one row in between the first side of the first bandpass filter 8 and the second side of the first bandpass filter 8. The second bandpass filter 9 comprises a plurality of second bandpass filter resonators, wherein the second bandpass filter resonators are aligned in one row in between the first side of the second bandpass filter 9 and the second side of the second bandpass filter 9.

[0054] A conductive separator 13 is aligned above the filter structure 5 in between the bandpass filters 8, 9. The conductive separator 13 is a portion of the lid 2b and is aligned such that the conductive separator 13 is positioned directly above the filter structure 5 and is positioned over the filter structure 5 such that the conductive separator 13 is in between the first bandpass filter 8 and the second bandpass filter 9. Preferably, the conductive separator 13 is separating all of the first bandpass filter resonators from all of the second bandpass filter resonators. Figure 3 is illustrating a relationship between the lid 2b and the filter structure 5 to indicate the position of the conductive separator 13 and the shielding elements over the filter structure 5 when the lid 2b is closed. The filter structure 5 is illustrated in a top-down view onto a top surface of the filter structure. The shielding elements are positioned in between the input resonator elements 6a to 6d of the input filter 6 and in between the output resonator elements 7a to 7d of the output filter 8. The conductive separator 13 is aligned in between the two bandpass filters 8, 9.

[0055] Figure 4 is showing a view of the housing 2 of the multi-band filter 1. The lid 2b comprises a cavity that can be logically partitioned into three areas 21 , 22, 23. The areas 21 , 22, 23 are subsequently aligned in a first direction, the first direction being a direction from the input port to the output port when the lid 2b is mounted to the filter structure 5. A first area 21 is on the side of the input port 3, a second area 22 is on a side of the output port and 4 and a third area 23 is in between the first area 21 and the second area 22 in the first direction.

[0056] The first area 21 is for covering the input filter 6. The first area 21 comprises the shielding elements that correspond to the input filter 6 and therefore comprises the first shielding element 11 . The second area 22 is for covering the output filter 7. The second area 22 comprises the shielding elements that correspond to the output filter 7 and therefore comprises the second shielding element 12. The third area 23 is for covering the bandpass filters 8, 9. The third area 23 comprises the conductive separator 13.

[0057] When mounted, the input filter 6 is aligned in the first area 21 , the output filter 7 is aligned in the second area 22, and the bandpass filters 8, 9 are aligned in the third area 23, wherein the bandpass filters 8, 9 are both extending in parallel to each other and parallel to the first direction. This is also illustrated in Figure 3.

[0058] The walls of the cavity of the lid 2a have different heights in the different areas 21 , 22, 23. The walls of the cavity have a hight of a value d1 in the first area. The walls of the cavity have a hight of a value d2 in the first area, wherein d2 > d1 . Preferably, the height of the cavity is the same in the first area 21 and in the third area 23.

[0059] Optionally, an absorber element 14 is aligned or multiple absorber elements are aligned inside the housing 2 in the third area 23. For example, an absorber element 14 is fixed to the inside of the cavity of the lid 2b in the third area 22. This is depicted by example in Figure 4. The absorber element 14 is aligned on a sidewall of the cavity to avoid a reflexion of electromagnetic waves. In a second embodiment of the invention, which essentially corresponds to the first embodiment, the dual-band filter 1 comprises at least one tuning element 30 that is extending from an outside of the housing 2 to an inside of the housing 2. An exemplary tuning element is depicted in Figure 5. The tuning element is a screw. The lid 2b comprises a through hole with an internal thread for the screw above the resonator elements of the second bandpass filter 9. A tuning can be performed by turning the tuning element 30. It is pointed out that it is preferable that the dualband filter 1 comprises multiple tuning elements. Preferably, a dedicated tuning element is positioned above each resonator element of the bandpass filters 8, 9. Figure 7 is illustrating exemplary S-Parameters of the multi-band filter 1. A frequency range in GHz is provided over the x-Axis. A Scattering Parameter in dB is provided over the y-Axis. The multi-band filter 1 is configured to provide a first passband 31 and a second passband 32, wherein the first passband 31 is located between 6Ghz and 7Ghz and wherein the second passband 32 is located between 7Ghz and 8Ghz. A stop band is provided above 8Ghz.

[0060] Figure 6 is depicting an antenna system 100, wherein the multi-band filter 1 is aligned in the antenna system and is configured to provide multi-band filtering in a transmitter or receiver path.

Claims

Claims1. Multi-band filter (1), the multi-band filter (1) comprising a housing (2) and a planar filter structure (5), wherein the housing is adjusted to cover the filter structure (5), and wherein the planar filter structure (5) comprises an input port (3) and an output port (4) and comprises structures that are forming: an input filter (6), wherein a first side of the input filter is coupled to the input port (3), wherein the input filter (6) is a band-stop filter or a lowpass filter, an output filter (7), wherein a first side of the output filter (7) is coupled to the output port (4), wherein the output filter (7) is a band-stop filter or a lowpass filter, and at least two bandpass filters (8, 9), wherein the bandpass filters (8, 9) are connected in parallel in between a second side of the input filter (6) and a second side of the output filter (7).

2. Multi-band filter (1) according to claim 1, wherein the bandpass filters (8, 9) are combline filters.

3. Multi-band filter (1) according to any one of the previous claims, wherein the input filter (6) is a combline filter and / or the output filter (7) is a combline filter.

4. Multi-band filter (1) according to claim 3, wherein the input filter (6) comprises a plurality of input filter resonators (6a, 6b, 6c, 6d), wherein a shielding-element (11) is aligned in and / or above the filter structure (5) between two of the input filter resonators (6a, 6b, 6c, 6d), and / or wherein the output filter (7) comprises a plurality of output filter resonators (7a, 7b, 7c, 7d), wherein a shielding-element (12) is aligned in and / or above the filter structure (5) between two of the output filter resonators (7a, 7b, 7c, 7d).

5. Multi-band filter (1) according to any one of the previous claims, wherein the filter structure (5) is a printed circuit board, PCB.

6. Multi-band filter (1) according to claim 5, wherein the input filter (6), the output filter (7) and the bandpass filters (8, 9) are formed on a first side of the PCB and a grounding layeris formed on a second side of the PCB, wherein the first side is a opposite side of the second side, wherein the input filter (6), the output filter (7) and / or the bandpass filters (8, 9) comprises a grounding connection that is provided by a via in the PCB.

7. Multi-band filter (1) according to any one of the previous claims, wherein a conductive separator (13) is aligned in and / or above the filter structure (5) in between the at least two bandpass filters (8, 9).

8. Multi-band filter (1) according to any one of the previous claims, wherein the housing (2) comprises a lid (2b) that comprises a cavity, wherein the input filter (6), the output filter (7) and the at least two bandpass filters (8, 9) are aligned in or below the cavity.

9. Multi-band filter (1) according to any one of the previous claims, wherein the housing (2) comprises three areas (21 , 22, 23) that are subsequently aligned in a first direction, the first direction being defined as a direction from the input port to the output port, wherein a first area (21) is on the side of the input port, a second area (22) is on a side of the output port and a third area (23) is in between the first area (21) and the second area (22) in the first direction, wherein the input filter (6) is aligned in the first area (21), the output filter (7) is aligned in the second area (22), and the at least two bandpass filters (8, 9) are aligned in the third area (23), wherein the bandpass filters (8, 9) are both extending in parallel to each other and parallel to the first direction.

10. Multi-band filter (1) according to claim 9, wherein an absorber element (14) is aligned inside the housing (2) in the third area (23).

11. Multi-band filter (1) according to any one of the previous claims, wherein a height (d1) of the housing above the input filter (6) is different to a height (d2) of the housing above at least one of the bandpass filters (8, 9); and / or wherein a height of the housing above the output filter (7) is different to a height (d2) of the housing above at least one of the bandpass filters (8, 9).

12. Multi-band filter (1) according to any one of the previous claims, the dual-band filter (1) comprising at least one tuning element that is extending from an outside of the housing to an inside of the housing.

13. Multi-band filter (1) according to any one of the previous claims, wherein the dual-band filter (1) is configured to provide a first passband and a second passband, wherein the firstpassband is preferably located between 6Ghz and 7Ghz, and wherein the second passband is located between 7Ghz and 8Ghz.

14. Multi-band filter (1) according to any one of the previous claims, wherein the input filter (6) and the output filter both comprise a same number of filter resonators.

15. Antenna System comprising the multi-band filter (1) according to any one of the previous claims.

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