Detuned Box Resonator RF Filter for Lower Passband Transmission Zeros

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Solution Overview

Problem

Generating transmission zeros below the passband in RF filters is challenging due to the complexity and spurious resonances introduced by negative cross couplings, which are difficult to assemble and maintain, especially in smaller filters operating at higher frequencies.

Innovation Solution

The use of a detuned box section resonator configuration with four resonators arranged to form a box, where the first, second, and fourth resonators resonate within the passband, and the third resonator resonates below the passband, creating a 180° phase shift difference between transmission paths to generate a transmission zero without negative cross couplings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If negative cross couplings are used to generate transmission zeros below the passband, then the filter response exhibits high local selectivity, but the device complexity increases significantly and spurious resonances are introduced

Engineering Contradiction:

Improvelocal selectivityVSAvoidfilter complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the negative cross coupling elements from the filter structure. Instead of using floating metal parts to create negative cross couplings, the invention uses a detuned resonator configuration where the resonator is deliberately detuned to resonate below the passband, achieving the same transmission zero effect without the harmful floating metal components.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the resonant frequency parameter of a resonator to be below the passband frequency range. By detuning the resonator to a lower frequency, the filter achieves transmission zeros below the passband through the detuned resonator's natural resonance characteristics rather than through negative cross coupling mechanisms.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If electrically floating metal parts are added to create negative cross couplings, then transmission zeros below the passband are achieved, but the assembly tolerances become challenging and manufacturing difficulty increases

Engineering Contradiction:

Improvetransmission zero accuracyVSAvoidassembly difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent merges the function of creating transmission zeros with the existing resonator structure. The detuned resonator serves dual purposes: it provides the primary resonance within the passband and simultaneously creates transmission zeros below the passband through its detuned frequency, eliminating the need for separate floating metal parts.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The detuned resonator is self-sufficient in generating transmission zeros. By simply adjusting the resonator's frequency to be below the passband, the structure automatically creates the desired transmission zero effect without requiring additional floating metal components or complex assembly procedures.

Inventive Principle:

Principle #25Self-service

3Manufacturing precision

If additional electrically floating metal parts are introduced to generate negative cross couplings, then transmission zeros are created, but spurious resonances are generated that degrade performance

Engineering Contradiction:

Improvefrequency response accuracyVSAvoidspurious resonances

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potential harm of detuned resonators (which could create unwanted resonances) into a benefit. By deliberately designing the resonator to detune to a specific frequency below the passband, the what would normally be a spurious resonance becomes a useful transmission zero that enhances filter selectivity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 simplifies the mechanical design, eliminates spurious resonances, and achieves a sharp cutoff at the lower end of the passband while maintaining acceptable stopband performance, reducing the complexity and cost of filter manufacturing.

Implementation Method 1

creating a 180° phase shift difference between transmission paths to generate a transmission zero

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 2

The first, second, and fourth resonators are configured to resonate within a passband of the filter, while the third resonator is configured to resonate outside the passband of the filter

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS20250023220A1Filters including detuned box section resonator configurations and/or resonators having beveled top surfaces

Publication Date: 2025.01.16 COMMSCOPE ITAL SRL

AI summary

Filters include a housing and at least first through fourth resonators are mounted within the housing. The first resonator is configured to couple with the second resonator and the third resonator but not the fourth resonator. The second resonator is configured to couple with the first resonator and the fourth resonator but not the third resonator. The third resonator is configured to couple with the first resonator and the fourth resonator but not the second resonator. The fourth resonator is configured to couple with the second resonator and the third resonator but not the first resonator. The first, second and fourth resonators are configured to resonate within a passband of the filter, while the third resonator is configured to resonate outside the passband of the filter.