Directional Coupler Low Pass Filter Flat Frequency Characteristic

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Solution Overview

Problem

Current directional couplers for wireless communication devices face challenges in maintaining a flat frequency characteristic for the degree of coupling, especially in wide frequency bands, leading to variations that affect transmission power control and battery life, particularly in mobile devices.

Innovation Solution

Incorporating a low pass filter unit between the secondary line and the coupling port, and optionally between the secondary line and the isolation port, to control signal frequencies and maintain a flat degree of coupling across a wide band, while also improving isolation and directivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a conventional directional coupler is used without a low pass filter unit, then the device complexity is low, but the degree of coupling exhibits non-flat frequency characteristic variations across wide frequency bands

Engineering Contradiction:

Improveflat frequency characteristic of degree of couplingVSAvoidstructure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

A low pass filter unit is introduced as an intermediary component between the secondary line and the coupling port. This filter unit mediates the frequency characteristics of the coupled signal, allowing high-frequency components to be attenuated while passing lower frequencies, thereby flattening the overall degree of coupling across wide frequency bands without fundamentally changing the coupler structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The frequency response parameters of the coupler are modified by adding the low pass filter unit. The filter's cutoff frequency and attenuation characteristics are optimized to compensate for the natural frequency variations in the directional coupler, transforming the non-flat frequency response into a flat one across the operating bandwidth

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If multiple couplers are used to cover different frequency bands, then the flat frequency characteristic is maintained for each band, but the device complexity and number of components increase

Engineering Contradiction:

Improveflat frequency characteristicVSAvoidfrequency band coverage

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The low pass filter unit serves multiple functions simultaneously: it flattens the degree of coupling across wide frequency bands, provides frequency selection, and enables a single coupler to handle multiple frequency bands. This multi-functionality eliminates the need for separate couplers for different frequency bands while maintaining flat frequency characteristics

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If the degree of coupling varies across frequency bands, then the device complexity is low, but the transmission power control accuracy deteriorates and battery life is reduced

Engineering Contradiction:

Improvenumber of componentsVSAvoidtransmission power control accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The low pass filter unit acts as an intermediary that stabilizes the degree of coupling measurement by removing high-frequency variations. This provides the automatic power control circuit with a more accurate and stable monitor signal, improving transmission power control accuracy without requiring additional components or complex circuitry

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enables a single coupler to maintain a flat degree of coupling over a wide frequency band, reducing the number of components needed, improving transmission power control, and enhancing battery life by minimizing insertion loss.

Implementation Method 1

a secondary line for electromagnetically coupling with the primary line to extract part of the transmission signal

Methodology Applied

Scientific EffectElectromagnetic coupling: Electromagnetic Induction

Implementation Method 2

a low pass filter unit having a function of low pass filter, disposed between the secondary line and the coupling port

Methodology Applied

Scientific EffectLow pass filtering: Filter (electronic)

Data Source

PatentUS9178264B2Directional coupler and wireless communication device

Publication Date: 2015.11.03 TDK CORP

AI summary

A directional coupler according to the present invention includes a primary line for transmitting a transmission signal; an input port for inputting the transmission signal to the primary line; an output port for outputting the transmission signal from the primary line; a secondary line for electromagnetically coupling with the primary line to extract part of the transmission signal; a coupling port provided at one end of the secondary line; an isolation port provided at the other end of the secondary line; and a low pass filter unit having a function of low pass filter, disposed between the secondary line and the coupling port.