Search

EP-4118706-B1 - CAVITY FILTERS AND FILTER MODULES THEREFOR

EP4118706B1EP 4118706 B1EP4118706 B1EP 4118706B1EP-4118706-B1

Inventors

  • BLANCO, Darwin

Dates

Publication Date
20260506
Application Date
20210311

Claims (19)

  1. A filtering module (204) for a cavity filter (100, 200), the filtering module comprising: a housing (102) defining an enclosed cavity (104), wherein a surface of the cavity is electromagnetically conductive; and a plurality of planar resonators (106) arranged within the cavity, one or more of the resonators being rotatable about an axis of rotation so as to vary an electric-field coupling between the resonator and other resonators of the plurality of resonators, wherein one or more of the plurality of resonators comprises a dielectric substrate (112) and an electrically conductive track (114) on the dielectric substrate.
  2. The filtering module according to claim 1, wherein the dielectric substrate (112) comprises ceramic.
  3. The filtering module according to claim 1 or 2, wherein the dielectric substrate (112) comprises a disc.
  4. The filtering module according to any one of claims 1 to 3, wherein the conductive track (114) is open-ended at a first end of the track, and electrically connected to the surface of the cavity at a second end of the track.
  5. The filtering module according to any one of claims 1 to 4, wherein the conductive track (114) is arranged in a straight line.
  6. The filtering module according to any one of the preceding claims, wherein the plurality of planar resonators (106) are arranged coaxially along an axis of the cavity (104).
  7. The filtering module according to claim 6, wherein the axis of rotation of the one or more resonators (106) corresponds to the axis of the cavity (104).
  8. The filtering module according to claim 6 or 7, wherein the cavity (104) is cylindrical, and wherein the axis of the cavity is a longitudinal axis of the cylindrical cavity.
  9. The filtering module according to any one of the preceding claims, further comprising an input (108, 208) for receiving a signal to be filtered, and applying the signal to a first resonator (106a) of the plurality of resonators.
  10. The filtering module according to any one of the preceding claims, further comprising an output (110, 210) for receiving a filtered signal from a second resonator (106c of the plurality of resonators, and outputting the filtered signal from the filtering module.
  11. A cavity filter (200), comprising: an input (208) for receiving a signal to be filtered; a plurality of filtering modules (204), each filtering module comprising: a cavity (104), wherein a surface of the cavity is electromagnetically conductive; and a plurality of resonators (106) arranged within the cavity, at least one of the resonators being movable so as to vary an electromagnetic coupling between the resonator and other resonators of the plurality of resonators; and an output (210) for outputting a filtered signal, wherein an input filtering module (204a) of the plurality of filtering modules is coupled to the input to receive the signal to be filtered, wherein each of the filtering modules is coupled to at least one other filtering module of the plurality of filtering modules via a magnetic coupling, and wherein an output filtering module (204c) of the plurality of filtering modules is coupled to the output and is configured to provide the filtered signal, and wherein one or more of the resonators of at least one filtering module of the plurality of filtering modules comprise a dielectric substrate and an electrically conductive track on the dielectric substrate.
  12. The cavity filter according to claim 11, wherein the plurality of filtering modules (204) further comprises one or more intermediate filtering modules (204b) arranged between the input filtering module (204a) and the output filtering module (204c).
  13. The cavity filter according to claim 12, wherein the one or more intermediate filtering modules (204b) are arranged in series between the input filtering module and the output filtering module.
  14. The cavity filter according to any one of claims 11 to 13, wherein an output resonator and an input resonator of coupled filtering modules of the plurality of filtering modules are substantially aligned so as to provide the magnetic coupling.
  15. The cavity filter according to claim 14, wherein the output resonator and the input resonator are aligned through an aperture (216) in a housing between the coupled filtering modules.
  16. The cavity filter according to any one of claims 11 to 15, wherein the plurality of resonators of at least one filtering module of the plurality of filtering modules are planar.
  17. The cavity filter according to any one of claims 11 to 16, wherein one or more of the resonators of at least one filtering module of the plurality of filtering modules are rotatable about an axis of rotation so as to vary an electromagnetic coupling between the resonator and other resonators of the plurality of resonators.
  18. The cavity filter according to any one of claims 11-15, wherein at least one of said filtering modules is configured according to any of claims 1-10.
  19. A wireless transmission and reception apparatus, comprising a cavity filter according to any one of claims 11 to 18.

Description

Technical field Embodiments of the disclosure relate to cavity filters, and particularly to radiofrequency or microwave cavity filters, component parts of such cavity filters, and wireless transmission and reception apparatuses comprising such cavity filters. Background Cavity filters at low frequencies (e.g., microwaves) are known for being expensive, heavy and bulky devices. The challenge in microwave filter design is to find a realizable topology that minimizes the number of resonators and satisfies the specification mask for the particular application (e.g., in terms of attenuation, phase group distortion, etc.). Often, the goal is to reduce the total volume of the filter, while keeping high performance at the lowest possible cost. Most of the time the filter mask does not require the same level of attenuation in both rejection bands of a passband filter, and therefore there is an increasing interest in using elliptical functions for communication applications because they can create bandpass filters with asymmetrical rejection bands. This capability to introduce arbitrary transmission zeros before and/or after the transmission band allows the design to be customized for a particular desired mask. This flexibility can be translated into a reduction in the number of required resonators and, thus, the size and weight of the filter. To produce a transmission zero, it is usually necessary to create cross-coupling between non-adjacent resonators, creating an alternative path where electromagnetic energy can flow through the device (from the input port to the output port). In other words, one resonator is coupled to at least two other resonators. This fact normally suggests geometries that are not inline and are difficult to generate, for example, in a combline filter. One successful inline and combline filter that can synthesize pseudo-elliptical responses was introduced by Macchiarella et al (R. Tkadlec and G. Macchiarella, "Pseudoelliptic Combline Filter in a Circularly Shaped Tube," 2018 IEEE/MTT-S International Microwave Symposium - IMS, Philadelphia, PA, 2018, pp. 1099-1102). The article "Design Methodology of a High-Q Tunable Coaxial Filter and Diplexer", discloses a feasibility study of realizing a high-Q tunable coaxial filter, which is tuned by a single rotational tuning element irrespective of the filter order. Further. the document "Pseudoelliptic Combline Filter in a Circularly Shaped Tube", discloses a configuration of a inline combline filter with pseudoelliptic response. In addition. The patent document DE3047466, discloses a filter with interconnected combline or interdigitally structured resonators been demonstrated using either multiple modes with the same resonator or new materials with high dielectric permittivity, such as ceramic materials. See, a paper by S. J. Fiedziuszko and S. Holmes ("Dielectric resonators raise your high-Q," in IEEE Microwave Magazine, vol. 2, no. 3, pp. 50-60, Sept. 2001). >> Page 2A Summary One inline combline filter that can synthesize pseudo-elliptical responses was introduced by Macchiarella et al, as noted above. The cross-coupling between non-adjacent resonators was created by misaligning the resonator axes. The complexity of the design is simple for three poles but increases with the order of the filter. The reported approach assumes that there is no coupling between two non-adjacent resonators, if there are at least two resonators between them (for example resonators 1 and 4 of an inline geometry). However, the design becomes very complex when the number of resonators increases (which is common for example in base stations and mobile communications). Besides, there is always spurious coupling for distant resonators that is difficult to neglect in a tuning stage. Separately, 3D resonator geometries are commonly used to obtain high Q-values, leading to the high volume/weight issue noted above. A considerable reduction in the volume has been demonstrated using multiple modes for the same resonator. However, it can be difficult to tune these modes independently and to compensate for thermal expansion when power is applied. Thus, using single mode or dual mode (same identical mode but orthogonal) resonators normally leads to a simpler realization of the filter (design and tuning) with respect to a greater number of modes. Summarizing, new filter topologies (that reduce the number of resonators) with high-Q values and/or small size would be beneficial to reduce the weight and the size of a filter solution. Moreover, a reduction in the dimension and/or complexity of the resonators is also appealing to simplify production and reduce cost. Embodiments of the disclosure seek to address these and other problems. In a first aspect, there is provided a cavity filter, as defined in claim 11, comprising: an input for receiving a signal to be filtered; a plurality of filtering modules, each filtering module comprising: a cavity, wherein a surface of the cavity is electrom