Modular Cavity Filter with Rotatable Resonators for Easier Tuning
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Solution Overview
Problem
Existing microwave cavity filters are bulky, heavy, and costly due to the complexity of resonator designs, particularly when using three-dimensional resonators and non-adjacent cross-coupling, which complicates tuning and increases spurious coupling.
Innovation Solution
A modular design with planar resonators arranged in multiple filtering modules, each with its own cavity, allowing magnetic coupling between modules and electric coupling within modules, combined with rotatable resonators to adjust electromagnetic coupling, using a hybrid approach of planar resonators and low-loss dielectric substrates to achieve high Q-values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If cavity filters are designed to operate at higher frequencies (e.g., 5 GHz and above), then the filter size must be reduced proportionally, but this reduction in size makes the filters increasingly susceptible to manufacturing errors and deviations from design specifications
Solution Approach 1:
The cavity filter is divided into multiple resonant cavities (e.g., input cavity, intermediate cavities, output cavity) that are coupled together. Each cavity operates at a fraction of the total frequency, allowing larger individual cavity dimensions that are less sensitive to manufacturing errors while achieving the required high overall operating frequency through the cascaded structure.
Solution Approach 2:
Multiple resonant modes are nested within the cavity structure, where higher-order resonant modes are utilized to achieve frequency multiplication. The cavities are designed to support multiple resonant frequencies, with the fundamental mode and higher-order modes both contributing to the overall filter performance at the desired high frequency.
2Reliability
If conventional cavity filters are used at millimeter-wave frequencies, then the filters become extremely small and highly sensitive to manufacturing errors, but increasing the size to reduce sensitivity contradicts the frequency scaling requirements
Solution Approach 1:
The filter is segmented into multiple cavities coupled through irises or apertures. This segmentation allows each cavity to be larger and less sensitive to manufacturing variations, while the combined structure achieves the required small overall footprint for millimeter-wave applications.
Solution Approach 2:
The design utilizes higher-order resonant modes to change the effective electrical length of the cavities without increasing their physical dimensions. By operating at higher resonant modes, the filter achieves the required frequency response with larger physical cavities that are more tolerant to manufacturing errors.
3Productivity
If the number of manufacturing steps is reduced for rapid production, then production time decreases, but the precision and quality of filter components may deteriorate
Solution Approach 1:
Multiple filter cavities and coupling structures are designed to be manufactured as integrated assemblies using techniques such as additive manufacturing or precision casting. This merging of multiple components into fewer manufacturing steps maintains high precision while significantly reducing production time and assembly complexity.
Solution Approach 2:
The manufacturing approach is changed from traditional multi-step machining to advanced manufacturing techniques like selective laser melting or precision investment casting. These techniques can produce complex cavity geometries with high precision in fewer steps, maintaining component quality while accelerating production.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design results in low-volume, low-weight filters with high Q-values, enabling easy tuning and reduced production costs, suitable for a broad range of applications including sub-6GHz solutions.
Implementation Method 1
cavity filters that operate by resonating at specific frequencies
Data Source
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AI summary
A first aspect of the disclosure provides a filtering module for a cavity filter, the filtering module comprising: a housing defining an enclosed cavity, wherein a surface of the cavity is electromagnetically conductive; and a plurality of planar resonators 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. A second aspect of the disclosure provides a cavity filter, 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 electromagnetically conductive; and a plurality of resonators 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 for outputting a filtered signal. An input filtering module of the plurality of filtering modules is coupled to the input to receive the signal to be filtered. Each of the filtering modules is coupled to at least one other filtering module of the plurality of filtering modules via a magnetic coupling. An output filtering module of the plurality of filtering modules is coupled to the output and is configured to provide the filtered signal.