Compact RF Filter Using Coupled Strip Resonators
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Solution Overview
Problem
Existing microstrip technology-based filter devices for radiofrequency applications result in large, voluminous filters due to the need for significant dephasing and impedance values, which are not always desirable, especially when aiming for high-order filters in the radiofrequency spectrum up to 300 GHz.
Innovation Solution
A filter device with an electrically conducting strip structure where resonators are closely spaced, with distances between their first ends being less than one tenth of the smallest effective fundamental resonant wavelength, creating a metamaterial structure that achieves a compact, high-order band-stop filter with reduced group velocity and negligible impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distributed constants filtering technique with unit cells is used, then filtering function is achieved, but filter volume increases progressively with filter order
Solution Approach 1:
Multiple resonators are merged into a single integrated structure with coupled resonant modes. The patent combines several resonating elements into one compact filter device where resonators interact through electromagnetic coupling, achieving high-order filtering functionality without proportionally increasing volume.
Solution Approach 2:
The filter structure embeds multiple resonant elements within a confined space. Resonators are arranged and coupled in a nested configuration where inner resonators interact with outer ones, allowing high-order filter responses to be achieved within a compact footprint that does not scale linearly with filter order.
2Reliability
If significant dephasing with discrete values (π or π/2) is obtained, then impedance delay line is achieved, but deviations between neighbouring resonators increase to λ/2 or λ/4
Solution Approach 1:
The patent transitions from discrete dephasing values (π, π/2) to continuous small dephasing values. By adjusting the coupling between closely spaced resonators, the system achieves precise phase control with deviations less than λ/10, enabling delay line functionality without requiring large physical separations between resonating elements.
3Reliability
If resonators are spaced with deviations of λ/2 or λ/4, then dephasing of π or π/2 is achieved, but filter volume increases
Solution Approach 1:
The invention changes the dephasing parameter from discrete large values (π, π/2) to continuous small values (less than λ/10). This parameter transformation allows the same filtering functionality to be achieved with resonators positioned much closer together, dramatically reducing the overall filter volume while maintaining the necessary phase relationships.
4Reliability
If high-order filters are designed with serial connection of filter devices, then filtering performance is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple filter functions into a single integrated device. Instead of connecting separate filter devices in series, the invention implements multiple resonators within one device that collectively provide high-order filtering performance, thereby reducing the number of discrete components and simplifying the overall device architecture.
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 solution results in a compact, high-performance filter device with a band-stop transfer function, reducing volume and achieving low-speed transmission alternatives, while maintaining effective filtering properties across the radiofrequency spectrum.
Implementation Method 1
create an effective fundamental resonant wavelength specific to each resonator on said surface of the substrate
Implementation Method 2
the distance between the first ends of two neighbouring resonators of this pair is less than one tenth of the smallest effective fundamental resonant wavelength of the plurality of resonators
Data Source
AI summary
A filter device includes a transmission line formed by an electrically conducting strip printed on a surface of an electrically insulating substrate, the conducting strip having two ends respectively forming the two sole input and output connection ports of the filter device, and a plurality of resonators, each resonator including an electrically conducting strip printed on the surface of the substrate. The conducting strip of each resonator has a first end coupled to the transmission line and at least one second end that is free or connected to a ground so as to create an effective fundamental resonant wavelength specific to each resonator. For each pair of neighboring resonators of the plurality of resonators, the distance between the first ends of the two neighboring resonators is less than one tenth of the smallest effective fundamental resonant wavelength of the plurality of resonators.