Filter Combiner With Directional Couplers For High Isolation

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Solution Overview

Problem

Existing filter combiners in mobile communications lack flexibility and high isolation between combined bands, especially when frequency hopping is used, and they are not suitable for advanced frequency systems due to critical transmission line lengths and impedance mismatch issues, making them impractical for retuning and high power handling.

Innovation Solution

A filter combiner design that includes a first and second directional coupler connected to filters, with a third filter in the first signal branch to prevent signal leakage and allow easy retuning, enabling high isolation and flexibility, even with impedance mismatch, and supporting high power handling and variable bandwidth configurations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional band filter combiners are used to combine frequency bands, then signal combining is achieved, but isolation between combined bands is insufficient and retuning is difficult

Engineering Contradiction:

Improveisolation between combined bandsVSAvoidretuning flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamic retuning capability by making the combiner structure adjustable in frequency. The directional couplers and filters are designed to be retunable, allowing the system to adapt to different frequency allocations and spectrum changes without requiring hardware replacement, thus resolving the contradiction between maintaining high isolation and achieving retuning flexibility.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes key parameters of the combiner components, specifically the coupling coefficients of directional couplers and the frequency characteristics of filters. By optimizing these parameters, the system achieves high isolation between combined bands while maintaining the ability to retune. The coupling coefficients are specifically designed to compensate for impedance variations, ensuring stable isolation performance across different tuning states.

Inventive Principle:

Principle #35Parameter changes

2Object-generated harmful factors

If filter combiners are designed for high isolation between bands, then signal leakage is reduced, but the structure becomes complex and retuning becomes difficult

Engineering Contradiction:

Improvesignal leakageVSAvoidcombiner structure

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent introduces directional couplers as intermediary components between the signal sources and the combiner output. These couplers provide isolation mechanisms that reduce signal leakage without requiring complex filter structures. The directional couplers act as mediators that manage signal paths and prevent interference, simplifying the overall combiner design while maintaining high isolation performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Power

If the combiner is designed to handle high power signals, then power handling capability is improved, but impedance mismatch issues increase affecting isolation

Engineering Contradiction:

Improvepower handling capabilityVSAvoidisolation performance

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent optimizes the coupling coefficients of directional couplers as key parameters to compensate for impedance mismatch effects at high power levels. By carefully selecting and adjusting these coupling parameters, the system maintains high isolation performance even when handling high power signals. The parameter optimization ensures that impedance variations do not degrade the isolation between combined bands.

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 provides high isolation between combined bands, allows easy retuning, and supports high power handling, reducing signal leakage and phase distortion, making it suitable for advanced frequency systems and flexible in frequency allocation.

Implementation Method 1

a first directional coupler, connected to at least one first filter and at least one second filter, and adapted to be connected to an antenna branch, and to a first signal branch

Methodology Applied

Scientific EffectElectromagnetic signal coupling: Electromagnetic Induction

Implementation Method 2

connected to at least one first filter and at least one second filter

Methodology Applied

Scientific EffectFrequency selective filtering: Filter (electronic)

Data Source

PatentUS7623005B2Filter combiner

Publication Date: 2009.11.24 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

The invention presents a filter combiner, in particular for mobile communications applications, adapted to be connected to an antenna (12), comprising a first directional coupler (13), connected to at least one first filter (15, 15a, 15b), to an antenna branch (12a), to at least one second filter (17, 17a, 17b), and to a first signal branch (20), the combiner also comprising a second directional coupler (21), connected to the at least one first filter (15, 15a, 15b), to a second signal branch (25), and to the at least one second filter (17, 17a, 17b). Further, the first directional coupler (13) is adapted to be connected to the first signal branch (20) via at least one third filter (29, 29a, 29b).