RF Via Impedance Balancing Using Nested Tuning Sections

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Solution Overview

Problem

Conventional methods for impedance balancing of long RF signals on densely packed PCBs, such as using quarter wave stubs, become impractical due to space constraints, leading to signal blockage and attenuation, especially at high frequency bands like Ku and Ka.

Innovation Solution

An apparatus and method involving a stack of PCB layers with a primary longitudinal structure and conductive column support, utilizing a principal tuning section with pad and anti-pad pairs at both ends of the RF via to achieve impedance matching, allowing for independent tuning of pad and anti-pad radii to balance the signal across the via path.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional quarter wave stubs are used for impedance balancing, then signal integrity can be improved, but the available space on densely packed PCBs is insufficient making the method impractical

Engineering Contradiction:

Improvesignal integrityVSAvoidavailable space on PCB

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent embeds the impedance balancing function within the existing via structure itself by adding conductive elements inside the via hole, rather than adding external stub structures. The via hole acts as a container for the impedance balancing mechanism, nesting the solution within the existing spatial footprint.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent transitions from a two-dimensional planar stub structure to a three-dimensional via-based structure by placing conductive elements vertically within the via hole. This vertical dimension allows impedance balancing without consuming additional lateral PCB space.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If tuning stubs are placed to balance impedance, then signal transmission can be improved, but the complexity of the structure increases with multiple stacked jogs and transitions

Engineering Contradiction:

Improvesignal transmissionVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The via structure is divided into multiple segments with different impedance characteristics along its length. Each segment (different via diameter portions) provides a specific impedance transformation, creating a stepped impedance profile that balances the signal without requiring complex external tuning structures.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The via structure simultaneously serves multiple functions: signal transmission, impedance transformation, and impedance balancing. The same via that carries the RF signal also provides the impedance matching function through its varied diameter sections, eliminating the need for separate tuning stubs.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If the circuit card is significantly populated with signal traces, then functional density is improved, but the area available for stub placement is reduced or eliminated

Engineering Contradiction:

Improvefunctional densityVSAvoidarea for stub placement

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The via structure is designed to self-balance the impedance through its own geometric characteristics (varied diameter sections) without requiring external stub structures. The via serves itself for both signal transmission and impedance balancing, eliminating the need for additional space-consuming components.

Inventive Principle:

Principle #25Self-service

4Adaptability or versatility

If long via routes are used to connect PCB layers, then connectivity between layers is achieved, but impedance imbalance and signal attenuation increase

Engineering Contradiction:

Improveconnectivity between layersVSAvoidimpedance balance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The via structure incorporates localized impedance transformations at specific sections (different diameter portions) to compensate for the overall impedance imbalance caused by the long via route. Each local section provides a specific impedance correction tailored to the signal requirements at that point in the transmission path.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11564316B2Apparatus and method for impedance balancing of long radio frequency (RF) via

Publication Date: 2023.01.24 LOCKHEED MARTIN CORP

AI summary

An apparatus comprising a stack of printed circuit board (PCB) layers having a primary longitudinal structure forming a radio frequency (RE) via including a principal tuning section (223) and a constant longitudinal structure (227) along a conductive column support (255) journaled through the layers in the via. The principal section (221) comprising a first tuning sub-assembly (229 A) in a first portion of the RE via above the longitudinal structure (227) and at an entrance of the primary longitudinal structure (221) and comprising a first set of pad, anti-pad pairs (445, 545, 645) tuned to receive an RE band. A second principal tuning sub-assembly (229B) in a second portion of the via below the longitudinal structure (227) and at an exit of the primary longitudinal structure and comprising a second set of pad, anti-pad pairs (445, 545, 645) tuned to receive the band and mirroring the first set of pairs.