Antenna Interconnect Length Tuning for Active Impedance Loads

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Solution Overview

Problem

In advanced antenna systems (AAS), the tight spacing of antenna elements leads to high electromagnetic coupling and active impedance load, causing performance degradation in power amplifiers (PAs) due to impedance mismatch, especially with fast beamsteering and Digital Pre-Distortion (DPD) systems, which are sensitive to these loads.

Innovation Solution

By altering the electrical length of interconnects between PA outputs and antenna elements/subarrays, specifically through varying routing trace lengths on a PCB, the impedance load is distributed more evenly, mitigating the mismatch and restoring performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If antenna elements are placed tightly together to form robust beams, then beamforming capability is improved, but electromagnetic coupling between antennas increases causing impedance mismatch

Engineering Contradiction:

Improvebeamforming capabilityVSAvoidimpedance match

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies different interconnect lengths to different antenna elements within the array. Each element's interconnect is specifically tailored to compensate for its local coupling conditions with neighboring elements, creating non-uniform electrical lengths that optimize each element's impedance match while maintaining tight spacing for beamforming

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the electrical length parameter of interconnects between PA outputs and antenna elements. By varying the length of routing traces on the PCB, the system adjusts the electrical length to distribute impedance load more evenly across all PA elements, mitigating the impedance mismatch caused by tight antenna spacing

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If beamsteering with phase shifts is applied to direct beams, then directional control is improved, but active impedance load increases causing PA performance degradation

Engineering Contradiction:

Improvedirectional controlVSAvoidPA performance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent pre-compensates for the active impedance load by designing unequal interconnect lengths before beamsteering operations. This preliminary impedance balancing ensures that when phase shifts are applied for beamsteering, the PA elements are already optimized to handle the resulting impedance variations, preventing performance degradation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Different interconnect lengths are assigned to different PA elements based on their specific positions and coupling conditions. This localized optimization allows each PA element to maintain proper impedance match even when beamsteering introduces phase shifts and active impedance loads

Inventive Principle:

Principle #3Local quality

3Loss of energy

If Digital Pre-Distortion is used to improve linearity, then efficiency is improved, but sensitivity to active impedance load increases

Engineering Contradiction:

ImproveefficiencyVSAvoidsensitivity to impedance load

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The patent implements preliminary impedance balancing through unequal interconnect lengths before the signal reaches the DPD circuitry. This pre-compensation reduces the active impedance load variations that DPD would otherwise be sensitive to, allowing DPD to operate more effectively without being overwhelmed by impedance mismatches

Inventive Principle:

Principle #10Preliminary action

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 approach improves PA efficiency and reduces performance degradation by evenly distributing impedance, allowing for more non-linear PAs and DPD usage without isolators, enhancing system efficiency and beamforming capabilities.

Implementation Method 1

the tight antenna spacing causes high electromagnetic coupling between the antennas

Methodology Applied

Scientific EffectElectromagnetic coupling:

Data Source

PatentUS12494834B2Advanced antenna system active impedance load mitigation

Publication Date: 2025.12.09 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

In an Advanced Antenna System, a desired power amplifier, PA, load distribution, which counters the mismatch of active impedance load, is achieved by altering the lengths of routing traces connecting PA outputs and corresponding antenna elements/subarrays. The combined output performance in the beam during active impedance load is then restored to the matched condition performance. This can be visualized as distributing the load impedance more evenly—ideally, on a circle—on a Smith chart.