Cavity Filter Tuning Elements for Thermal Stability
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Solution Overview
Problem
Existing radio frequency filters with cavity structures face challenges in cost-effective fabrication and temperature stability, particularly when large filters are made, as they require complex processes and are prone to operational malfunctions due to thermal expansion.
Innovation Solution
The design incorporates tuning elements with a lower thermal expansion coefficient than the cover material, such as copper or iron, which are press-fitted or soldered into through holes in the cover, eliminating the need for tuning screws and nuts, allowing for cost-effective and stable frequency tuning across temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If tuning screws and fastening nuts are used for frequency tuning, then frequency tuning capability is achieved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts and eliminates the tuning screws and fastening nuts from the cavity filter structure, replacing them with a simplified tuning mechanism that integrates directly into the housing, thereby reducing device complexity while maintaining frequency tuning capability
Solution Approach 2:
The patent merges the tuning function directly into the housing structure by forming sunken portions and integrating tuning elements, eliminating the need for separate coupling structures of screws and nuts, thus simplifying the overall device
2Ease of operation
If sunken portions are formed on the cover by die casting for large filters, then frequency tuning is enabled, but manufacturing cost increases
Solution Approach 1:
The patent segments the housing into a base portion and a cover portion that can be separately manufactured and then assembled, allowing the sunken portions to be formed on the cover by simpler, more cost-effective processes rather than requiring complex die casting of the entire housing
Solution Approach 2:
The sunken portions are pre-formed on the cover during a simpler manufacturing process before final assembly, enabling frequency tuning capability to be built into the structure without incurring high die casting costs for large filters
3Weight of stationary object
If aluminum or aluminum alloy is used for the housing and cover, then weight and fabrication cost are reduced, but temperature stability deteriorates due to thermal expansion
Solution Approach 1:
The patent applies different materials to different parts of the housing structure - the main housing and cover remain aluminum for lightness, while specific components such as the resonant elements or tuning structures are made from materials with low thermal expansion coefficients to maintain dimensional stability in critical areas
Solution Approach 2:
The patent employs composite construction by combining aluminum housing with components made from materials having different thermal expansion properties, creating a hybrid structure that achieves both light weight and temperature stability
4Measurement precision
If the distance between sunken portions and resonant elements is reduced for tuning, then frequency tuning precision is improved, but manufacturing precision requirements increase
Solution Approach 1:
The sunken portions are pre-formed on the cover with predetermined dimensions and positions during the manufacturing process, establishing the initial distance relationships between tuning elements and resonant elements before final assembly and tuning adjustments
Solution Approach 2:
The patent incorporates adjustable tuning elements that can be positioned within the sunken portions, allowing the distance between tuning elements and resonant elements to be dynamically adjusted during frequency tuning to achieve precise control without requiring extremely tight manufacturing tolerances
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 configuration enables simple, low-cost fabrication of large filters with stable filtering characteristics, as the tuning elements compensate for temperature-induced changes in resonant frequencies, maintaining optimal performance.
Implementation Method 1
the tuning elements have a lower thermal expansion coefficient than that of the cover. Therefore, when a temperature change occurs, the tuning elements compensate for a change in resonant frequencies due to a distance change between the cover and resonant elements
Implementation Method 2
a resonant element such as a dielectric resonant (DR) element or a metal resonant rod accommodated in each cavity, to thereby generate ultra-high frequency resonance
Data Source
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AI summary
The present invention relates to a wireless frequency filter having a cavity structure, the wireless frequency filter comprising: a housing having a hollow interior and an open surface on one side so as to structure a cavity; a cover for sealing the open surface of the housing; and resonance members located in the hollow space of the housing, wherein the cover is provided with through-holes in the vicinity corresponding to each resonance member, and tuning structures for frequency tuning fitted in a shape to block the through-holes, the tuning structure being made of material having coefficient of thermal expansion which is lower or higher than that of the material of the cover.