Coupled-Inductor Duplexer Layout for RF Leakage Isolation

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Solution Overview

Problem

RF signal leakage due to shared ground inductance and parasitic components limits the isolation between transmit and receive filters in duplexers, especially in crowded frequency bands like LTE networks, where steep roll-off and low thermal drift are required to efficiently utilize bandwidth.

Innovation Solution

Incorporating coupled inductors to offset or cancel the coupling between transmit and receive filters caused by common ground inductance, which are electromagnetically coupled to induce a voltage without direct current flow, thereby reducing RF signal leakage and enhancing isolation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If shared ground inductance is used to connect transmit and receive filters, then device complexity is reduced, but RF signal leakage increases and isolation deteriorates

Engineering Contradiction:

Improveground connection structureVSAvoidRF signal leakage

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent applies the 'Blessing in disguise' principle by converting the harmful effect of shared ground inductance (which causes RF signal leakage) into a beneficial cancellation mechanism. Coupled inductors are introduced that generate an opposing voltage to cancel the leakage signal through electromagnetic coupling, thereby transforming the harmful ground inductance effect into a controlled cancellation system that improves isolation while maintaining the simple shared ground structure.

Inventive Principle:

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

2Object-generated harmful factors

If coupled inductors are added to cancel RF signal leakage, then isolation is improved, but device complexity increases

Engineering Contradiction:

ImproveRF signal leakageVSAvoidinductor structure

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies the 'Intermediary' principle by introducing coupled inductors as intermediary elements between the shared ground inductance and the transmit/receive filters. These coupled inductors act as mediators that generate compensating voltages to cancel RF signal leakage without requiring complete redesign of the ground connection system. The coupled inductors serve as intermediate components that bridge the existing ground structure with the isolation enhancement function.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If steep roll-off is implemented in crowded frequency bands, then bandwidth utilization is improved, but insertion loss increases

Engineering Contradiction:

Improvebandwidth utilizationVSAvoidinsertion loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent applies the 'Parameter changes' principle by carefully adjusting the electrical parameters of the coupled inductors (such as coupling coefficient, inductance values, and connection topology) to achieve steep roll-off characteristics in crowded frequency bands. By optimizing these parameters, the system can provide sharp frequency selectivity for efficient bandwidth utilization while minimizing the insertion loss that would otherwise result from aggressive filtering in congested spectral environments.

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 use of coupled inductors significantly improves the isolation between the Tx and Rx ports by canceling RF signal leakage, achieving better than 58 dB isolation over specific frequency bands, thus enhancing the duplexer's performance in crowded frequency spectra.

Implementation Method 1

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11271541B2Microwave duplexer using coupled inductors to improve isolation

Publication Date: 2022.03.08 MURATA MFG CO LTD

AI summary

A duplexer includes a duplexer package having a transmit terminal, an antenna terminal, a receive terminal and at least one package ground terminal, a transmit filter disposed within the duplexer package, and a receive filter disposed within the duplexer package. Coupled first and second inductors, the first inductor connected to the transmit filter and the second inductor connected to the receive filter, are configured to cancel, at least in part, RF signal leakage between the transmit filter and the receive filter.