Miniature Tunable Filter With Solid Metal Rod
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Solution Overview
Problem
Current tunable filters are either large in size, have limited RF power handling, high loss, or are not suitable for mobile applications due to their fixed frequency and limited tuning range, especially at higher frequencies.
Innovation Solution
A miniature tunable filter design featuring coaxial-type resonators with a mechanically tunable solid metal rod and low-loss metal coating, coupled with a linear motor for precise tuning, which allows for wide frequency range operation with low impedance and minimal RF losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If miniature ceramic filters use high dielectric constant ceramic materials to reduce size, then the filter size is reduced, but the RF power handling capability is limited
Solution Approach 1:
The filter combines ceramic dielectric material with metal components (tuning rod, coupling structures) to create a composite resonator system. The ceramic provides miniaturization through high dielectric constant while the metal components provide high power handling capability, resolving the contradiction between size reduction and power handling.
2Adaptability or versatility
If varactor tuned filters are used for frequency tuning, then frequency adjustment is enabled, but loss increases and tuning range is limited at frequencies greater than 500 MHz
Solution Approach 1:
The patent replaces the electrical varactor tuning mechanism with a mechanical tuning rod system. The tuning rod is physically moved into and out of the ceramic resonator to adjust frequency, eliminating the high loss associated with varactor diodes while providing wide tuning range capability through the mechanical adjustment of the rod position.
3Adaptability or versatility
If YIG tuned filters are used for wide frequency range operation, then frequency tuning range is expanded, but DC power consumption increases and RF power handling is limited due to ferrite saturation
Solution Approach 1:
The patent replaces the magnetically-tuned YIG ferrite system with a mechanically-tuned ceramic resonator system. Instead of using DC current to magnetically saturate ferrite material for frequency control, the invention uses mechanical movement of a tuning rod within the ceramic resonator, eliminating DC power consumption while maintaining wide frequency tuning range capability.
4Power
If Air Core machined filters are used for high power handling, then RF power handling capability is improved, but the filter size becomes large and unsuitable for mobile applications
Solution Approach 1:
The filter combines ceramic dielectric material with metal components to create a composite resonator system. The ceramic provides miniaturization through high dielectric constant while the metal components (tuning rod, coupling structures, shielding) provide high power handling capability, resolving the contradiction between size reduction and power handling.
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
The design achieves high power handling and low loss capabilities, enabling wide frequency tuning with minimal insertion loss and efficient RF performance, making it suitable for multiband telecommunication and radar systems.
Implementation Method 1
A low impedance coaxial section surrounds at least a portion of the mechanically tunable tuning rod to create an effective microwave short-circuit at a resonant frequency of the miniature tunable filter
Implementation Method 2
both the exterior surface of the ceramic dielectric cavity and the exterior surface of the mechanically tunable tuning rod comprise polished surfaces with low surface roughness for minimal radio frequency (RF) losses
Implementation Method 3
the miniature tunable filter further comprises a cavity coupling aperture between the at least two adjacent coaxial-type resonators, wherein the cavity coupling aperture couples microwave energy between each coaxial-type resonator
Data Source
AI summary
Described is a miniature tunable filter, comprising at least two adjacent coaxial-type resonators coupled to one another. Each coaxial-type resonator comprises a metal-coated ceramic dielectric cavity having a tuning rod passage formed therethrough. A tuning rod is inserted through the tuning rod passage, such that the miniature tunable filter is tuned by moving the tuning rod into and out of the tuning rod passage of the ceramic dielectric cavity. A low impedance coaxial section surrounds at least a portion of the tuning rod to create an effective microwave short-circuit at a resonant frequency of the miniature tunable filter, which results in very wide tuning and low insertion loss. In a desired aspect, the tuning rod is a solid metal tuning rod. The combination of a solid metal tuning rod with a ceramic coaxial-type resonator results in high radio frequency power handling.