CPW Filter with Slow-Wave Resonance for Wide Stopband

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing filters with wide stopbands are limited in their ability to suppress high-order harmonic waves, require large areas, and are costly due to the need for complex designs and multiple resonators.

Innovation Solution

A filtering unit utilizing a CPW transmission line, tapered CPW transmission line, and ground stub to generate a slow-wave feature, which pushes high-order harmonic waves to higher frequencies, achieving a wider stopband while reducing filter size and cost through symmetrically disposed slow-wave resonance units and stepped impedance transmission lines.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multiple identical resonators are cascaded to enhance out-of-band harmonic-wave suppression, then the stopband suppression is improved, but the filter area becomes relatively large and costs increase

Engineering Contradiction:

Improveout-of-band suppressionVSAvoidfilter area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent changes the electrical length parameters of transmission line sections to create harmonic resonators with specific resonance frequencies. By adjusting the lengths of transmission line sections (e.g., making them odd multiples of quarter-wavelengths), the patent achieves wide stopband coverage without requiring multiple cascaded resonators, thus reducing filter area while maintaining suppression performance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent divides the filter into multiple resonant branches, each contributing to stopband suppression at different frequency ranges. This segmentation allows the filter to achieve wide stopband coverage through coordinated action of individual branches rather than requiring multiple complete resonator cascades, reducing overall area

Inventive Principle:

Principle #1Segmentation

2Reliability

If a hybrid structure of microstrip and CPW is used to generate transmission zeroes, then the out-of-band suppression is improved, but the stopband is limited to 6.52 times of baseband signal and area is relatively large

Engineering Contradiction:

Improveharmonic wave suppressionVSAvoidstopband range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent uses parameter changes in transmission line lengths and impedance values to create multiple transmission zeroes at different frequency locations. By carefully selecting the electrical lengths of various transmission line sections, the patent achieves both harmonic suppression and extended stopband range beyond the limitations of conventional hybrid structures

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite structure combining different types of transmission lines (microstrip and CPW) with specific impedance characteristics. This composite approach allows generation of multiple transmission zeroes while achieving wider stopband coverage, overcoming the limitations of using单一 structure types

Inventive Principle:

Principle #40Composite materials

3Reliability

If a series of short-circuit lines are added to quarter-wave CPW resonator to generate transmission zeroes, then the out-of-band suppression is improved, but the stopband is expanded to only five times of baseband signal and filter area is relatively large

Engineering Contradiction:

Improvestopband suppressionVSAvoidstopband expansion

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #35Parameter changes

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 effectively expands the stopband up to 14.2 times the baseband signal with a suppression degree of -21.5 dB, reduces filter area, and lowers costs while maintaining high performance and bandwidth.

Implementation Method 1

A filtering unit utilizing a CPW transmission line, tapered CPW transmission line, and ground stub to generate a slow-wave feature, which pushes high-order harmonic waves to higher frequencies

Methodology Applied

Scientific EffectSlow-wave effect:

Implementation Method 2

tapered CPW transmission line

Methodology Applied

Scientific EffectImpedance transformation:

Data Source

PatentEP3346543B1Filtering unit and filter

Publication Date: 2020.11.25 HUAWEI TECH CO LTD

Figure 1~2
Figure 3~4
Figure 5~6

AI summary

A filtering unit is provided, and the filtering unit includes two mutually coupled slow-wave resonance units. Each resonance unit includes a CPW transmission line, a tapered CPW transmission line, and a ground stub, and can generate a slow-wave feature to push a high-order harmonic wave of a baseband signal to a high frequency, so as to implement a wide stopband feature. In addition, a slow-wave effect is used to properly design a size of a filter, to reduce an entire area of the filter and reduce costs. Moreover, two resonance units are coupled, to enhance passband performance of the filter, increase bandwidth, increase in-passband flatness, and reduce an insertion loss.