RFID Transmitter Power Tracking Loop for Coaxial Cable Attenuation

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Solution Overview

Problem

Long range RFID systems using coaxial cables face unpredictable RF signal attenuation due to varying cable lengths, leading to inconsistent performance in determining RFID tag locations across different retail environments.

Innovation Solution

A power tracking loop, or gain control system, is integrated into the transmitter antenna circuitry, which includes a High Power Amplifier (HPA) and a gain control circuit with a comparator to maintain a desired RF signal strength at the antenna, automatically adjusting the gain based on detected signal levels to compensate for attenuation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If coaxial cables of varying lengths are used to connect the MEU to transmitter antennae, then the system can adapt to different retail establishment sizes, but the RF signal strength at the antenna becomes unpredictable due to signal attenuation

Engineering Contradiction:

Improveadaptability to different retail establishment sizesVSAvoidpredictability of RF signal strength

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the actual RF signal strength at the antenna is measured and compared to the desired signal strength. Based on this comparison, the system automatically adjusts the transmitter power output to compensate for cable attenuation. This closed-loop control ensures that despite varying cable lengths, the antenna receives a consistent desired signal strength, thus maintaining reliability while allowing adaptability to different installation configurations.

Inventive Principle:

Principle #23Feedback

2Reliability

If the RF transmitter power is increased to compensate for cable attenuation, then the signal strength at the antenna can be maintained, but the power consumption and potential interference increase

Engineering Contradiction:

Improvesignal strength at antennaVSAvoidpower consumption of transmitter

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent employs dynamic power adjustment where the transmitter power is not fixed but continuously adapted based on the measured signal strength at the antenna. The system adjusts the power output in real-time to maintain the desired signal level, increasing power only when necessary (e.g., when longer cables are used) and reducing it when shorter cables are present. This dynamic approach optimizes power consumption while ensuring reliable signal transmission.

Inventive Principle:

Principle #15Dynamics

3Reliability

If manual power adjustment is used for each antenna, then the RF signal strength can be optimized, but the system complexity and installation time increase

Engineering Contradiction:

ImproveRF signal strength optimizationVSAvoidnumber of power gain controls

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements a self-service mechanism where the system automatically measures the RF signal strength at each antenna and adjusts the power output without requiring manual intervention. The controller autonomously determines the appropriate power level based on the measured signal strength and cable characteristics, eliminating the need for manual power adjustment by installers. This automation reduces installation time and complexity while maintaining optimized RF signal strength.

Inventive Principle:

Principle #25Self-service

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 solution ensures consistent and predictable RF signal levels are maintained at the antenna, improving the accuracy of RFID tag location determination regardless of coaxial cable length, thereby enhancing system performance across varying retail environments.

Implementation Method 1

The RF input signals can range from +4 dBm to +18 dBm and are applied to a High Power Amplifier (HPA). The HPA has a nominal gain of +23 dB. This means that an RF input of +4 dBm will result in an amplified output of +27 dBm.

Methodology Applied

Scientific EffectSignal amplification:

Implementation Method 2

The gain control circuit includes a comparator that compares a proportional DC signal (derived from the UHF RF signal at the output of the HPA) with a manually derived signal (set with a potentiometer) to cause a HIGH or LOW gain control signal to be applied to the HPA

Methodology Applied

Scientific EffectAutomatic gain control:

Implementation Method 3

RF power transmitted over coaxial cable loses strength from the input to the output of the cable. Two parameters generally define the loss for a particular type of cable. These parameters are cable length and frequency of the RF signals transmitted over the coaxial cable.

Methodology Applied

Scientific EffectSignal attenuation: Absorption (EM radiation)

Data Source

PatentUS8010067B2Long range RFID transmitter power tracking loop

Publication Date: 2011.08.30 ABL IP HLDG LLC

AI summary

A high power amplifier having an automatic gain control circuit, the high power amplifier being coupled between the output end of an RF signal carrying coaxial cable and a transmitting antenna to automatically compensate for RF signal attenuation over the length of the coaxial cable.